Cdc42 is an essential GTPase that belongs to the Rho family of Ras-like GTPases. These proteins act as molecular switches by responding to exogenous and/or endogenous signals and relaying those signals to activate downstream components of a biological pathway. Cdc42 transduces signals to the actin cytoskeleton to initiate and maintain polarized growth and to mitogen-activated protein morphogenesis. In Saccharomyces cerevisiae, Cdc42 plays an important role in multiple actin-dependent morphogenetic events such as bud emergence, mating-projection formation, and pseudohyphal growth []. In mammalian cells, Cdc42 regulates a variety of actin-dependent events and induces the JNK/SAPK protein kinase cascade, which leads to the activation of transcription factors within the nucleus []. Cdc42 mediates these processes through interactions with a myriad of downstream effectors, whose number and regulation we are just starting to understand. In addition, Cdc42 has been implicated in a number of human diseases through interactions with its regulators and downstream effectors [].
The Rho-type GTPase Cdc42 regulates cell morphology and signal transduction in eukaryotic cells. The Cdc42 effector (CEP) or binder of Rho GTPase (BORG) proteins are involved in the organisation of the actin cytoskeleton []. They may function as negative regulators of Rho GTPase signaling [].This family consists of Cdc42 effector proteins, including CEP1-5 from humans.
This entry represents the Cdc42 (a GTPase) binding domain superfamily. The domain is largely unstructured in the absence of Cdc42 []. Proteins containing this domain include the probable tyrosine-protein kinase sid-3 and the activated CDC42 kinase 1.
This entry represents the Cdc42 (a GTPase) binding domain. The domain is largely unstructured in the absence of Cdc42 []. Proteins containing this domain include the tyrosine-protein kinase sid-3 [], the ERBB receptor feedback inhibitor 1, the activated CDC42 kinase 1 and the probable tyrosine-protein kinase kin-25.
This entry represents Cdc42 effector protein 2 (also known as Binder of Rho GTPases 1). It is probably involved in the organisation of the actin cytoskeleton [, ].
Activated CDC42 kinase 1 (Ack1) is a non-receptor tyrosine kinase (NRTK) that is implicated in metastatic behaviour, cell spreading and migration, and epidermal growth factor receptor (EGFR) signalling []. It interacts with a number of transmembrane receptor tyrosine kinases and is involved in several cell signalling pathways. Its activation has been linked to cancer progression [].
This entry represents a group of Cdc42-binding proteins known as SPECs (for small protein effector of Cdc42), including SPEC1 and SPEC2 from humans. SPECs modulate the activity of the Rho GTPase Cdc42, which plays important roles in actin polymerization and kinase signaling []. SPEC1 and SPEC2 play a role in F-actin accumulation in activated T lymphocytes and may play a role in early contractile events in phagocytosis [].
This entry represents the PH domain found in Cdc24 from budding yeasts and Scd1 from fission yeasts. Cdc24 and Scd1 are guanine nucleotide exchange factors (GEFs) for Cdc42 [, ].
T-lymphoma invasion and metastasis-inducing protein 1 (Tiam1) is a guanine exchange factor (GEF) for CDC42 and the Rho-family GTPase Rac1, which plays an important role in cell-matrix adhesion and in cell migration [, ]. Tiam1 is involved in multiple steps of tumorigenesis [].
This entry represent the RhoGAP domain found in ARHGAP6 and ARHGAP36.Rho GTPase activating protein 6 (ARHGAP6/RHOGAP6) shows GAP activity towards RhoA, but not towards Cdc42 and Rac1 []. ARHGAP6 is often deleted in microphthalmia with linear skin defects syndrome (MLS); MLS is a severe X-linked developmental disorder []. ARHGAP36 is a potent antagonist of PKAsignalling [].
Protein phosphatase 1 regulatory subunit 12C (PPP1R12C, also known as p85) is a myotonic dystrophy kinase-related Cdc42 binding kinase (MRCK) substrate. It is associated with protein phosphatase 1delta (PP1delta) through its N terminus. This association is required for the regulation of both the catalytic activities and the assembly of actin cytoskeleton. Its C terminus is involved in dimerisation and interaction with other proteins [].
This entry represents a domain found in the Inka proteins, including Inka1 and Inka2. They are inhibitors of PAK4, a metazoan-specific kinase acting downstream of Cdc42 [, ]. Danio rerio (Zebrafish) Inka1 is required for the proper migration of neural crest cells during embryonic development [].
This entry includes INKA1 and INKA2. They are inhibitors of PAK4, a metazoan-specific kinase acting downstream of Cdc42 [, ]. Danio rerio (Zebrafish) Inka1 is required for the proper migration of neural crest cells during embryonic development []. Homologues are known only from chordates and contain a FAM212 domain.
Rho GTPase activating protein 6 (ArhGAP6/RHOGAP6) shows GAP activity towards RhoA, but not towards Cdc42 and Rac1 []. ArhGAP6 is often deleted in microphthalmia with linear skin defects syndrome (MLS); MLS is a severe X-linked developmental disorder [].This family also includes ARHGAP36, which is a potent antagonist of PKA signalling [].
This entry includes MISP/MISP3 from animals. MISP is an actin-binding protein that functions in spindle orientation probably by linking the astral microtubules (MTs) to the actin cytoskeleton [, ]. It has been shown to regulate IQGAP1 and Cdc42 to ensure proper mitotic progression and correct spindle orientation []. The function of MISP3 is not clear.
Dynamin-binding protein (DNMBP, also known as Tuba) is a scaffold protein that links dynamin with actin-regulating proteins. It binds a variety of actin regulatory proteins, including N-WASP, CR16, WAVE1, WIRE, PIR121, NAP1, and Ena/VASP proteins, via a C-terminal SH3 domain []. It plays a critical role in ciliogenesis and nephrogenesis, most likely via Cdc42 activation [].
Serine/threonine-protein kinase MRCK (myotonic dystrophy kinase-related CDC42-binding kinase) is an serine/threonine-protein kinase which is an important downstream effector of CDC42 and plays a role in actin-myosin regulation and activities including cell adhesion, motility and invasion [, ]. Three isoforms have been described in mammals: alpha, beta and gamma [, ]. This entry represents the serine/threonine-protein kinase MRCK gamma [].
This entry represents the CRIB domain. Many putative downstream effectors of the small GTPases Cdc42 and Rac contain a GTPase binding domain (GBD), also called p21 binding domain (PBD), which has been shown to specifically bind the GTP bound form of Cdc42 or Rac, with a preference for Cdc42 [, ]. The most conserved region of GBD/PBD domains is the N-terminal Cdc42/Rac interactive binding motif (CRIB), which consists of about 16 amino acids with the consensus sequence I-S-x-P-x(2,4)-F-x-H-x(2)-H-V-G [].Although the CRIB motif is necessary for the binding to Cdc42 and Rac, it is not sufficient to give high-affinity binding [, ]. A less well conserved inhibitory switch (IS) domain responsible for maintaining the proteins in a basal (autoinhibited) state is located C-terminaly of the CRIB-motif [, , ].GBD domains can adopt related but distinct folds depending on context. Although GBD domains are largely unstructured in the free state, the IS domain forms an N-terminal β-hairpin that immediately follows the conserved CRIB motif and a central bundle of three α-helices in the autoinhibited state. The interaction between GBD domains and their respective G proteins leads to the formation of a high-affinity complex in which unstructured regions of both the effector and the G protein become rigid. CRIB motifs from various GBD domains interact with Cdc42 in a similar manner, forming an intermolecular β-sheet with strand β-2 of Cdc42. Outside the CRIB motif, the C-terminal of the various GBD domains are very divergent and show variation in their mode of binding to Cdc42, perhaps determining the specificity of the interaction. Binding of Cdc42 or Rac to the GBD domain causes a dramatic conformational change, refolding part of the IS domain and unfolding the rest [, , , , ].Some proteins known to contain a CRIB domain are listed below:Mammalian activated Cdc42-associated kinases (ACKs), nonreceptor tyrosine kinases implicated in integrin-coupled pathways.Mammalian p21-activated kinases (PAK1 to PAK4), serine/threonine kinases that modulate cytoskeletal assembly and activate MAP-kinase pathways.Mammalian Actin nucleation-promoting factor WAS (also known as Wiskott-Aldrich Symdrom Proteins, WASPs), non-kinase proteins involved in the organisation of the actin cytoskeleton.Yeast STE20 and CLA4, the homologues of mammalian PAKs. STE20 is involved in the mating/pheromone MAP kinase cascade.
This entry represents the CRIB domain superfamily. Many putative downstream effectors of the small GTPases Cdc42 and Rac contain a GTPase binding domain (GBD), also called p21 binding domain (PBD), which has been shown to specifically bind the GTP bound form of Cdc42 or Rac, with a preference for Cdc42 [, ]. The most conserved region of GBD/PBD domains is the N-terminal Cdc42/Rac interactive binding motif (CRIB), which consists of about 16 amino acids with the consensus sequence I-S-x-P-x(2,4)-F-x-H-x(2)-H-V-G [].Although the CRIB motif is necessary for the binding to Cdc42 and Rac, it is not sufficient to give high-affinity binding [, ]. A less well conserved inhibitory switch (IS) domain responsible for maintaining the proteins in a basal (autoinhibited) state is located C-terminaly of the CRIB-motif [, , ].GBD domains can adopt related but distinct folds depending on context. Although GBD domains are largely unstructured in the free state, the IS domain forms an N-terminal beta; hairpin that immediately follows the conserved CRIB motif and a central bundle of three alpha; helices in the autoinhibited state. The interaction between GBD domains and their respective G proteins leads to the formation of a high-affinity complex in which unstructured regions of both the effector and the G protein become rigid. CRIB motifs from various GBD domains interact with Cdc42 in a similar manner, forming an intermolecular beta;-sheet with strand beta;-2 of Cdc42. Outside the CRIB motif, the C-termini of the various GBD domains are very divergent and show variation in their mode of binding to Cdc42, perhaps determining the specificity of the interaction. Binding of Cdc42 or Rac to the GBD domain causes a dramatic conformational change, refolding part of the IS domain and unfolding the rest [, , , , ].Some proteins known to contain a CRIB domain are listed below:Mammalian activated Cdc42-associated kinases (ACKs), nonreceptor tyrosine kinases implicated in integrin-coupled pathways.Mammalian p21-activated kinases (PAK1 to PAK4), serine/threonine kinases that modulate cytoskeletal assembly and activate MAP-kinase pathways.Mammalian Actin nucleation-promoting factor WAS proteins (WASPs), non-kinase proteins involved in the organisation of the actin cytoskeleton.Yeast STE20 and CLA4, the homologues of mammalian PAKs. STE20 is involved in the mating/pheromone MAP kinase cascade.
Epithelial Cell Transforming Sequence 2 (Ect2) is a guanine nucleotide exchange factor (GEF) that catalyses the exchange of GDP for GTP. Like other GEFs, Ect2 serves as molecular switches in diverse signaling pathways, including cell polarity, mitotic spindle assembly, cytokinesis, etc [, , ]. Ect2 interacts with several members of the Rho GTPase family including, RhoA, RhoB, RhoC, RhoG, Rac1 and Cdc42 [, , , , ]. Ect2 regulates the formation of the actomyosin contractile ring at mitotic exit through activation of RhoA and functions in metaphase for the process of spindle assembly through activation of Cdc42 []. Ect2 is regulated through a number of mechanisms including phosphorylation, intracellular localization and intra- and inter-molecular interactions []. Ect2 is established as a human oncogene []. It is highly expressed in a variety of human tumors including brain lung, bladder, esophageal, pancreatic and ovarian tumors [, , , , ]. Ect2 is also suggested to play a role in neuronal differentiation and brain development [].
ICAP-1 is a serine/threonine-rich protein that binds to the cytoplasmic domains of beta-1 integrins in a highly specific manner, binding to a NPXY sequence motif on the beta-1 integrin. The cytoplasmic domains of integrins are essential for cell adhesion, and the fact that phosphorylation of ICAP-1 by interaction with the cell-matrix implies an important role of ICAP-1 during integrin-dependent cell adhesion []. Over expression of ICAP-1 strongly reduces the integrin-mediated cell spreading on extracellular matrix and inhibits both Cdc42 and Rac1. In addition, ICAP-1 induces release of Cdc42 from cellular membranes and prevents the dissociation of GDP from this GTPase []. An additional function of ICAP-1 is to promote differentiation of osteoprogenitors by supporting their condensation through modulating the integrin high affinity state [].
RasGRF1 belong to the RasGRF family. It regulates both Ras and Rac signalling pathways []. It has been implicated in memory formation, postnatal growth, glucose homeostasis and photoreception [].RasGRF is a Ras family guanine nucleotide exchange factor sharing homology with Saccharomyces cerevisiae Cdc25 that stimulates nucleotide exchange on S. cerevisiae RAS []. RasGRF N-terminal region contains a Dbl homology (DH) domain which is generally present in GEFs for the Rho family of small G proteins, whereas the C-terminal Cdc25-related domain is linked to Ras GTPase signalling []. The presence of regulatory domains for Rho and Ras GTPases implicates the role of RasGRF in the control of the both pathways []. Two RasGRF, RasGRF1 and 2, have been identified in mammals []. Their function can be inhibited by its interaction with Cdc42 in its inactive GDP bound form. Reciprocally, the effects of Cdc42 on cytoskeletal dynamics can be inhibited by RasGRF1/2 [].
This entry represents the PH domain of guanine nucleotide exchange factor DBS. The DBS PH domain participates in binding to both the Cdc42 and RhoA GTPases []. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner [].DBS, also called MCF2L or OST, functions as a Rho GTPase guanine nucleotide exchange factor (RhoGEF), facilitating the exchange of GDP and GTP. It was originally isolated from a cDNA screen for sequences that cause malignant growth. It plays roles in regulating clathrin-mediated endocytosis and cell migration through its activation of Rac1 and Cdc42 [, ]. Depending on cell type, DBS can also activate RhoA and RhoG [, ]. DBS contains a Sec14-like domain [], spectrin-like repeats, a RhoGEF or Dbl homology (DH) domain, a Pleckstrin homology (PH) domain [], and an SH3 domain.
Serine/threonine-protein kinase MRCK (myotonic dystrophy kinase-related CDC42-binding kinase) is an serine/threonine-protein kinase which is an important downstream effector of CDC42 and plays a role in actin-myosin regulation and activities including cell adhesion, motility and invasion [, ]. Three isoforms have been described in mammals: alpha, beta and gamma [, ]. This entry represent the serine/threonine-protein kinase MRCK alpha. It also includes the Drosophila homologue Genghis khan (Gek) [, ].
Formin-binding protein 1-like (FNBP1L, also known as Toca-1) is part of the Toca-1-N-WASP complex that induces the formation of filopodia and endocytic vesicles []. FNBP1L consists of an F-BAR domain, a Cdc42 binding site and an SH3 domain []. It belongs to the CIP4 (Cdc42 interacting protein-4) subfamily of the F-BAR (F for FCH, Fer-CIP4 homology domain) protein family. The F-BAR proteins have been implicated in cell membrane processes such as membrane invagination, tubulation and endocytosis [].
Serine/threonine-protein kinase MRCK (myotonic dystrophy kinase-related CDC42-binding kinase) is an serine/threonine-protein kinase which is an important downstream effector of CDC42 and plays a role in actin-myosin regulation and activities including cell adhesion, motility and invasion [, ]. Three isoforms have been described in mammals: alpha, beta and gamma [, ]. This entry represent the serine/threonine-protein kinase MRCK beta. It may have important roles in tumour progression [].
Cell cycle progression protein 1 (CCPG1), also known as cell cycle progression restoration protein 8 (CPR8) [], is a scaffold protein that interacts with the Rho guanine nucleotide exchange factor Dbs and modulates its exchange specificity. CCPG1 binds to the Dbl homology/pleckstrin homology domain tandem motif of Dbs and inhibits its exchange activity toward RhoA, but not Cdc42 []. CCPG1 may be involved in cell cycle regulation [].
Rho GTPase-activating protein 26 (ARHGAP26), also known as GTPase regulator associated with focal adhesion kinase (GRAF), is a GTPase-activating protein for the small GTPases of the Rho family RhoA and CDC42 [, ]. GRAF influences cytoskeletal changes mediated by Rho proteins []. It is recognised as a tumor suppressor []. GRAF contains an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, a Rho GAP domain, and a C-terminal SH3 domain. The SH3 domain of GRAF binds PKNbeta, a target of the small GTPase Rho [].
This entry represents Tax1-binding protein 3, also known as TIP-1, which is a PDZ domain-containing protein that functions in a wide variety of biological events through selective interaction with different proteins. It interacts with the RhoA effector protein rhotekin []. It also associates with glutaminase L [], potassium channel Kir2.3 []and NMDA receptors []. In humans, Tax1-binding protein 3 has been shown to be involved in the activation of Cdc42 by the viral protein HPV16 E6 []. TIP-1 can have both an oncogenic function or act as a tumor suppressor, probably by modulating the transcriptional activity of beta-catenin [, ].
Tiam1 is a guanine exchange factor (GEF) for CDC42 and the Rho-family GTPase Rac1, which plays an important role in cell-matrix adhesion and in cell migration [, ]. Tiam1 is involved in multiple steps of tumorigenesis [].This entry represents the CC and Ex subdomain found in the PH-CC-Ex globular domain of the Tiam1 and Tiam2 proteins (T-lymphoma invasion and metastasis). The CC subdomain forms an antiparallel coiled coil with two long α-helices, together with the C-terminal Ex subdomain they form a small globular domain comprising three α-helices. The CC subdomain of the Tiam2 PHCCEx domain follows the C-terminal alpha1 helix of the PH subdomain through a four-residue linker [].
This entry represents the SH3 domain of GRAF.Rho GTPase-activating protein 26 (ARHGAP26), also known as GTPase regulator associated with focal adhesion kinase (GRAF), is a GTPase-activating protein for the small GTPases of the Rho family RhoA and CDC42 [, ]. GRAF influences cytoskeletal changes mediated by Rho proteins []. It is recognised as a tumor suppressor []. GRAF contains an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, a Rho GAP domain, and a C-terminal SH3 domain. The SH3 domain of GRAF binds PKNbeta, a target of the small GTPase Rho [].
GRAF2, also called Rho GTPase activating protein 10 (ARHGAP10) or PS-GAP, is a GAP with activity towards Cdc42 and RhoA []. It regulates caspase-activated p21-activated protein kinase-2 (PAK-2p34). GRAF2 interacts with PAK-2p34, leading to its stabilization and decrease of cell death []. It is highly expressed in skeletal muscle, and is involved in alpha-catenin recruitment at cell-cell junctions []. GRAF2 contains an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, a Rho GAP domain, and a C-terminal SH3 domain. The SH3 domain of GRAF binds PKNbeta, a target of the small GTPase Rho []. This entry represents the SH3 domain of GRAF2.
This entry represents the SH3 domain of FNBP1L.Formin-binding protein 1-like (FNBP1L, also known as Toca-1) is part of the Toca-1-N-WASP complex that induces the formation of filopodia and endocytic vesicles []. FNBP1L consists of an F-BAR domain, a Cdc42 binding site and an SH3 domain []. It belongs to the CIP4 (Cdc42 interacting protein-4) subfamily of the F-BAR (F for FCH, Fer-CIP4 homology domain) protein family. The F-BAR proteins have been implicated in cell membrane processes such as membrane invagination, tubulation and endocytosis [].
Fus1 is required at the cell surface for cell fusion during the mating response in yeast. It requires Bch1 and Bud7, which are Chs5-Arf1 binding proteins, for localization to the plasma membrane []. It acts as a scaffold protein to assemble a cell surface complex which is involved in septum degradation and inhibition of the NOG pathway to promote cell fusion []. The SH3 domain of Fus1 interacts with Bin1, a formin that controls the assembly of actin cables in response to Cdc42 signalling. It has been shown to bind the motif, R(S/T)(S/T)SL, instead of PxxP motifs [].
This entry represents the SH3 domain of DBS.DBS, also called MCF2L or OST, functions as a Rho GTPase guanine nucleotide exchange factor (RhoGEF), facilitating the exchange of GDP and GTP. It was originally isolated from a cDNA screen for sequences that cause malignant growth. It plays roles in regulating clathrin-mediated endocytosis and cell migration through its activation of Rac1 and Cdc42 [, ]. Depending on cell type, DBS can also activate RhoA and RhoG [, ]. DBS contains a Sec14-like domain [], spectrin-like repeats, a RhoGEF or Dbl homology (DH) domain, a Pleckstrin homology (PH) domain [], and an SH3 domain.
ARHGEF9 (Rho guanine nucleotide exchange factor 9, also called PEM2 or collybistin) selectively activates Cdc42 by exchanging bound GDP for free GTP []. It is highly expressed in the brain and it interacts with gephyrin, a postsynaptic protein associated with GABA and glycine receptors. Mutations in the ARHGEF9 gene cause X-linked mental retardation with associated features like seizures, hyper-anxiety, aggressive behavior, and sensory hyperarousal [, , ]. ARHGEF9 contains a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains [].This entry represents the SH3 domain of ARHGEF9.
Alpha-PIX, also called Rho guanine nucleotide exchange factor 6 (ARHGEF6) or Cool (Cloned out of Library)-2, activates small GTPases by exchanging bound GDP for free GTP []. It acts as a GEF for both Cdc42 and Rac1, and is localized in dendritic spines where it regulates spine morphogenesis []. It controls dendritic length and spine density in the hippocampus. Mutations in the ARHGEF6 gene cause X-linked intellectual disability in humans [, ]. PIX proteins contain an N-terminal SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains, and a C-terminal leucine-zipper domain for dimerization. This entry represents the SH3 domain of alpha-PIX.
Dynamin-binding protein (DNMBP,also known as Tuba) is a scaffold protein that links dynamin with actin-regulating proteins. It binds a variety of actin regulatory proteins, including N-WASP, CR16, WAVE1, WIRE, PIR121, NAP1, and Ena/VASP proteins, via a C-terminal SH3 domain []. It plays a critical role in ciliogenesis and nephrogenesis, most likely via Cdc42 activation [].The four N-terminal SH3 domains of DNMBP binds the GTPase dynamin, which plays an important role in the fission of endocytic vesicles []. This entry represents the first N-terminal SH3 domain.
Dynamin-binding protein (DNMBP, also known as Tuba) is a scaffold protein that links dynamin with actin-regulating proteins. It binds a variety of actin regulatory proteins, including N-WASP, CR16, WAVE1, WIRE, PIR121, NAP1, and Ena/VASP proteins, via a C-terminal SH3 domain []. It plays a critical role in ciliogenesis and nephrogenesis, most likely via Cdc42 activation [].The four N-terminal SH3 domains of DNMBP binds the GTPase dynamin, which plays an important role in the fission of endocytic vesicles []. This entry represents the second N-terminal SH3 domain.
Dynamin-binding protein (DNMBP, also known as Tuba) is a scaffold protein that links dynamin with actin-regulating proteins. It binds a variety of actin regulatory proteins, including N-WASP, CR16, WAVE1, WIRE, PIR121, NAP1, and Ena/VASP proteins, via a C-terminal SH3 domain []. It plays a critical role in ciliogenesis and nephrogenesis, most likely via Cdc42 activation [].The four N-terminal SH3 domains of DNMBP binds the GTPase dynamin, which plays an important role in the fission of endocytic vesicles []. This entry represents the third N-terminal SH3 domain.
Dynamin-binding protein (DNMBP, also known as Tuba) is a scaffold protein that links dynamin with actin-regulating proteins. It binds a variety of actin regulatory proteins, including N-WASP, CR16, WAVE1, WIRE, PIR121, NAP1, and Ena/VASP proteins, via a C-terminal SH3 domain []. It plays a critical role in ciliogenesis and nephrogenesis, most likely via Cdc42 activation [].The C-terminal SH3 domains of DNMBP bind to N-WASP and Ena/VASP proteins, which are key regulatory proteins of the actin cytoskeleton []. This entry represents the first C-terminal SH3 domain.
This entry represents the F-BAR domain of FNBP1L.Formin-binding protein 1-like (FNBP1L, also known as Toca-1) is part of the Toca-1-N-WASP complex that induces the formation of filopodia and endocytic vesicles []. FNBP1L consists of an F-BAR domain, a Cdc42 binding site and an SH3 domain []. It belongs to the CIP4 (Cdc42 interacting protein-4) subfamily of the F-BAR (F for FCH, Fer-CIP4 homology domain) protein family. The F-BAR proteins have been implicated in cell membrane processes such as membrane invagination, tubulation and endocytosis [].
GRAF2, also called Rho GTPase activating protein 10 (ARHGAP10) or PS-GAP, is a GAP with activity towards Cdc42 and RhoA []. It regulates caspase-activated p21-activated protein kinase-2 (PAK-2p34). GRAF2 interacts with PAK-2p34, leading to its stabilization and decrease of cell death []. It is highly expressed in skeletal muscle, and is involved in alpha-catenin recruitment at cell-cell junctions []. GRAF2 contains an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, a Rho GAP domain, and a C-terminal SH3 domain. The SH3 domain of GRAF binds PKNbeta, a target of the small GTPase Rho [].
Rsr1 is a member of the Rap subfamily of the Ras family that is found in fungi. In budding yeasts, Rsr1 is involved in selecting a site for bud growth on the cell cortex, which directs the establishment of cell polarization. The Rho family GTPase cdc42 and its GEF, cdc24, then establish an axis of polarized growth by organizing the actin cytoskeleton and secretory apparatus at the bud site. It is believed that cdc42 interacts directly with Rsr1 in vivo [, ]. In filamentous fungi, polar growth occurs at the tips of hypha and at novel growth sites along the extending hypha. In Ashbya gossypii, Rsr1 is a key regulator of hyphal growth, localizing at the tip region and regulating in apical polarization of the actin cytoskeleton [].Most Ras proteins contain a lipid modification site at the C terminus, with a typical sequence motif CaaX, where a = an aliphatic amino acid and X = any amino acid. Lipid binding is essential for membrane attachment, a key feature of most Ras proteins [].
There are two forms of Pix proteins: alpha Pix (also called Rho guanine nucleotide exchange factor (GEF) 6, 90Cool-2 or ARHGEF6) and beta Pix (GEF7, p85Cool-1 or ARHGEF7), which activate small GTPases by exchanging bound GDP for free GTP. betaPix contains an N-terminal SH3 domain, a RhoGEF/DH domain, a PH domain, a GIT1 binding domain (GBD), and a C-terminal coiled-coil (CC) domain []. It acts as a GEF for both Cdc42 and Rac1 [], and plays important roles in regulating neuroendocrine exocytosis, focal adhesion maturation, cell migration, synaptic vesicle localization, and insulin secretion [, , , ]. alphaPix differs in that it contains a calponin homology (CH) domain, which interacts with beta-parvin, N-terminal to the SH3 domain. alphaPix is an exchange factor for Rac1 and Cdc42 and mediates Pak activation on cell adhesion to fibronectin. Mutations in alphaPix can cause X-linked mental retardation. alphaPix also interacts with Huntington's disease protein (htt), and enhances the aggregation of mutant htt (muthtt) by facilitating SDS-soluble muthtt-muthtt interactions. The DH-PH domain of a Pix was required for its binding to htt. In the majority of Rho GEF proteins, the DH-PH domain is responsible for the exchange activity [, , , , ].This entry represents the PH domain of ARHGEF6 and ARHGEF7.
RasGRF2 belongs to the RasGRF family. It is a dual Ras/Rac guanine nucleotide exchange factor (GEF) that has been shown to be necessary for long-term potentiation in situ [, ]. It is also involved in T-cell signalling responses through Ras GTPases []. RasGRF2 has been linked to alcoholism [].RasGRF is a Ras family guanine nucleotide exchange factor sharing homology with Saccharomyces cerevisiae Cdc25 that stimulates nucleotide exchange on S. cerevisiae RAS []. RasGRF N-terminal region contains a Dbl homology (DH) domain which is generally present in GEFs for the Rho family of small G proteins, whereas the C-terminal Cdc25-related domain is linked to Ras GTPase signalling []. The presence of regulatory domains for Rho and Ras GTPases implicates the role of RasGRF in the control of the both pathways []. Two RasGRF, RasGRF1 and 2, have been identified in mammals []. Their function can be inhibited by its interaction with Cdc42 in its inactive GDP bound form. Reciprocally, the effects of Cdc42 on cytoskeletal dynamics can be inhibited by RasGRF1/2 [].
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions []. This entry represents the BAR domain found in fungal proteins with similarity to Saccharomyces cerevisiae Reduced viability upon starvation protein 161 (Rvs161p) and Schizosaccharomyces pombe Hob3 (homologue of Bin3). S. cerevisiae Rvs161p plays a role in regulating cell polarity, actin cytoskeleton polarization, vesicle trafficking, endocytosis, bud formation, and the mating response. It forms a heterodimer with another BAR domain protein Rvs167p. Rvs161p and Rvs167p share common functions but are not interchangeable [, ]. Their BAR domains cannot be replaced with each other and the overexpression of one cannot suppress the mutant phenotypes of the other. S. pombe Hob3 is important in regulating filamentous actin localization and may be required in activating Cdc42 and recruiting it to cell division sites []. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions [].
T-lymphoma invasion and metastasis-inducing protein 1 (Tiam1) is a guanine exchange factor (GEF) for CDC42 and the Rho-family GTPase Rac1, which plays an important role in cell-matrix adhesion and in cell migration [, ]. Tiam1 is involved in multiple steps of tumorigenesis [].Tiam2 has been shown to localise to the nuclear envelope and to regulate Rac1 activity at the nuclear envelope which regulates the perinuclear actin cap []. It has been shown to promote invasion and motility of non-small cell lung cancer cells []. It has also been shown to promote epithelial-to-mesenchymal transition and results in proliferation and invasion in liver cancer cells []. This entry includes a group of guanine nucleotide exchange factors, including Tiam1/2 from humans and Sif from Drosophila [, , ]. Tiam1/2 are activators of the Rho GTPase Rac1 and critical for cell morphology, adhesion, migration, and polarity [].
WAS/WASL-interacting protein family member 1 (WIPF1, also known as WIP) is involved in a wide variety of cellular functions,including cellular signalling, endocytosis and actin cytoskeletonremodelling []. It binds to and stabilises N-WASP and WASP []. WIP and WASP can form a complex, which plays an important role in Arp2/3-mediated actin polymerisation and is regulated by Cdc42 (a small GTPase of the Rho family) [, ]. WIP can also participates in the reorganisation of the actin-based cytoskeleton and stabilises actin filaments in a WASP-independent manner []. In blood cells, WIP participates in conveying WASP to areas of active actin assembly following antigen-receptor and chemokinereceptor signalling [, , , ]. WIP deficiency is linked to Wiskott-Aldrich syndrome 2, which is an immunodeficiency disorder characterised by eczema, thrombocytopenia, recurrent infections, defective T-cell proliferation, and impaired natural killer cell function [].
DOCK family members are evolutionarily conserved guanine nucleotide exchange factors (GEFs) for Rho-family GTPases []. DOCK proteins are required during several cellular processes, such as cell motility and phagocytosis. The N-terminal SH3 domain of the DOCK proteins functions as an inhibitor of GEF, which can be relieved upon its binding to the ELMO1-3 adaptor proteins, after their binding to active RhoG at the plasma membrane [, ]. DOCK family proteins are categorised into four subfamilies based on their sequence homology: DOCK-A subfamily (DOCK1/180, 2, 5), DOCK-B subfamily (DOCK3, 4), DOCK-C subfamily (DOCK6, 7, 8), DOCK-D subfamily (DOCK9, 10, 11) []. This entry represents DOCK9 (also known as Zizimin). DOCK9 and DOCK11 activate Cdc42 [, ].
This entry represents the catalytic domain of serine/threonine kinase p21-activated kinase (PAK) 3.PAK3 is highly expressed in the brain. It is implicated in neuronal plasticity, synapse formation, dendritic spine morphogenesis, cell cycle progression, neuronal migration, and apoptosis [, ]. Inactivating mutations in the PAK3 gene cause X-linked non-syndromic mental retardation, the severity of which depends on the site of the mutation [, ]. PAK3 belongs to the group I PAKs.Group I PAKs contain a PBD (p21-binding domain) overlapping with an AID (autoinhibitory domain), a C-terminal catalytic domain, SH3 binding sites and a non-classical SH3 binding site for PIX (PAK-interacting exchange factor). PAKs are Rho family GTPase-regulated kinases that serve as important mediators in the function of Cdc42 (cell division cycle 42) and Rac [].
PAK2 plays a role in pro-apoptotic signaling. It is cleaved and activated by caspases leading to morphological changes during apoptosis []. PAK2 is also activated in response to a variety of stresses including DNA damage, hyperosmolarity, serum starvation, and contact inhibition, and may play a role in coordinating the stress response []. PAK2 also contributes to cancer cell invasion through a mechanism distinct fromthat of PAK1 []. PAK2 belongs to the group I PAKs.Group I PAKs contain a PBD (p21-binding domain) overlapping with an AID (autoinhibitory domain), a C-terminal catalytic domain, SH3 binding sites and a non-classical SH3 binding site for PIX (PAK-interacting exchange factor). PAKs are Rho family GTPase-regulated kinases that serve as important mediators in the function of Cdc42 (cell division cycle 42) and Rac [].This entry corresponds to the PAK2 C-terminal catalytic domain.
Diaphanous-related formins (Drfs) are a family of formin homology (FH) proteins that act as effectors of Rho small GTPases during growth factor-induced cytoskeletal remodelling, stress fibre formation, and cell division []. Drf proteins are characterised by a variety of shared domains: an N-terminal GTPase-binding domain (GBD), formin-homology domains FH1, FH2 () and FH3 (), and a C-terminal conserved Dia-autoregulatory domain (DAD) that binds the GBD.This entry represents the GBD, which is a bifunctional autoinhibitory domain that interacts with and is regulated by activated Rho family members. Mammalian Drf3 contains a CRIB-like motif within its GBD for binding to Cdc42, which is required for Cdc42 to activate and guide Drf3 towards the cell cortex where it remodels the actin skeleton [].
This entry represents the PX domain found in Rho GTPase-activating protein 32 (ARHGAP32, also known as RICS). RICS is a Rho GTPase-activating protein for cdc42 and Rac1. It is implicated in the regulation of postsynaptic signaling and neurite outgrowth. An N-terminal splicing variant of RICS containing additional PX and Src Homology 3 (SH3) domains, also called PX-RICS, is the main isoform expressed during neural development. PX-RICS is involved in neural functions including axon and dendrite extension, postnatal remodeling, and fine-tuning of neural circuits during early brain development []. The PX domain is involved in targeting of proteins to PI-enriched membranes, and may also be involved in protein-protein interaction []. The PX domain of PX-RICS specifically binds phosphatidylinositol 3-phosphate (PI3P), PI4P, and PI5P [].
IRTKS (insulin receptor tyrosine kinase substrate; brain-specific angiogenesis inhibitor 1-associated protein 2-like protein 1 or BAIAP2L1) is an I-BAR (Bin/amphipysin/Rvs) domain containing protein. I-BAR domain is a type of the BAR domain, which forms an anti-parallel all-helical dimer, with a curved (banana-like) shape, that promotes membrane tubulation. The BAR domain containing proteins can be classified into three types: BAR, F-BAR and I-BAR. BAR and F-BAR proteins generate positive membrane curvature, while I-BAR proteins induce negative curvature [].IRTKS binds small GTPase Rac rather than Cdc42 []. It serves as an adaptor of the insulin receptor (IR), modulates IR-IRS1-PI3K-AKT signalling via regulating the phosphorylation of IR []. It has been linked to the formation of actin-rich membrane protrusions, called pedestals, during the infection process of enterohemorrhagic Escherichia coli [].
This superfamily contains the N-terminal domain of diaphanous, a subclass of formins whose members are regulated by the binding of a small GTP-binding protein of the Rho subfamily. These proteins are characterised by a variety of shared domains: an N-terminal GTPase-binding domain (GBD), formin-homology domains FH1, FH2 and FH3, and a C-terminal conserved Dia-autoregulatory domain (DAD) that binds the GBD. This N-terminal domain corresponds to the GBD, a bifunctional autoinhibitory domain that interacts with and is regulated by activated Rho family members. Mammalian Drf3 contains a CRIB-like motif within its GBD for binding to Cdc42, which is required for Cdc42 to activate and guide Drf3 towards the cell cortex where it remodels the actin skeleton [, ].
This entry includes Harmonin-binding protein USHBP1 also known as MCC2) and colorectal mutant cancer protein known as MCC. MCC has been found to suppresses cell proliferation and the Wnt/b-catenin pathway in colorectal cancer cells [, ]. It may works as a scaffold protein regulating cell movement and able to bind Scrib, beta-catenin and NHERF1/2 []. MCC1 inhibits DNA binding of b-catenin/TCF/LEF transcription factors, and it is involved in cell migration independently of RAC1, CDC42 and p21-activated kinase (PAK) activation [, , ].MCC2 protein binds the first PDZ domain of AIE-75 with its C-terminal amino acids -DTFL. A possible role of MCC2 as a tumour suppressor has been put forward. The carboxyl terminus of the predicted protein was DTFL which matched the consensus motif X-S/T-X-phi (phi: hydrophobic amino acid residue) for binding to the PDZ domain of AIE-75 [, ].
Members of Rho family are small G proteins that transduce signals from plasma-membrane receptors and control cell adhesion, motility and shape by actin cytoskeleton formation. Like all other GTPases, Rho proteins act as molecular switches, with an active GTP-bound form and an inactive GDP-bound form. The active conformation is promoted by guanine-nucleotide exchange factors, and the inactive state by GTPase-activating proteins (GAPs), which stimulate the intrinsic GTPase activity of small G proteins.This entry represents Rho GTPase activating protein 27 (ARHGAP27, also known as CIN85-associated multi-domain-containing Rho GTPase-activating protein 1, CAMGAP1), a binding protein for Cbl-interacting protein of 85kDa (CIN85), an adaptor protein involved in the endocytic process of several receptor tyrosine kinases. It also has activity towards Rac1 and Cdc42 [].
Ephexin-1 is a RhoGEF (Rho-type guanine nucleotide exchange factor) that activates RhoA, Tac1, and Cdc42 by exchanging bound GDP for free GTP []. It is expressed mainly in the brain in a region associated with movement control. It regulates the stability of postsynaptic acetylcholine receptor (AChR) clusters and thus plays a critical role in the maturation and neurotransmission of neuromuscular junctions []. Ephexin-1 directly interacts with the ephrin receptor EphA4 and their coexpression enhances the ability of ephexin-1 to activate RhoA []. It is required for normal axon growth and EphA-induced growth cone collapse []. Ephexin-1 contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin Homology (PH) and SH3 domains. This entry represents the SH3 domain.
This entry represents the SH3 domain found in srGAP proteins 1, 2 and 3. srGAP1 (also called ARHGAP13) is a key GTPase activating protein (GAP) downstream of Slit-Robo pathway, and has been shown to inhibit neuronal migration and glioma cell invasion by reducing the activation of Cdc42 []. srGAP2 (ARHGAP34) regulates neuronal morphogenesis through the ability of its F-BAR domain to regulate membrane deformation and induce filopodia formation []. srGAP3 (ARHGAP14) interacts with lamellipodin at the cell membrane and regulates Rac-dependent cellular protrusions []. The SLIT-ROBO Rho GTPase-activating protein (srGAP) family consists of four members: srGAP1, -2, -3 and -4. They contain F-BAR, RhoGAP and SH3 domains. Their RhoGAP domain is involved in negative regulation of Rho GTPase activities important for cytoskeleton rearrangement []. The srGAP family members have an "inverse F-BAR"or IF-BAR domain that is distinct from other F-BAR domains such as FBP17. They are multifunctional adaptor proteins involved in various aspects of neuronal development [].
This entry represents the SH3 domain of srGAP4. srGAP4 is highly expressed in hematopoietic cells and may play a role in lymphocyte differentiation []. It is able to stimulate the GTPase activity of three members of Rho GTPases, Rac1, Cdc42 and RhoA. In the nervous system, srGAP4 has been detected in differentiating neurites and may be involved in axon and dendritic growth [].The SLIT-ROBO Rho GTPase-activating protein (srGAP) family consists of four members: srGAP1, -2, -3 and -4. They contain F-BAR, RhoGAP and SH3 domains. Their RhoGAP domain is involved in negative regulation of Rho GTPase activities important for cytoskeleton rearrangement []. The srGAP family members have an "inverse F-BAR"or IF-BAR domain that is distinct from other F-BAR domains such as FBP17. They are multifunctional adaptor proteins involved in various aspects of neuronal development [].
VAV2 is widely expressed and functions as a guanine nucleotide exchange factor (GEF) for RhoA, RhoB and RhoG and also activates Rac1 and Cdc42 []. It is implicated in many cellular and physiological functions including blood pressure control, eye development, neurite outgrowth and branching, EGFR endocytosis and degradation, and cell cluster morphology, among others [, , , , ]. It has been reported to associate with Nek3. VAV proteins contain several domains that enable their function: N-terminal calponin homology (CH), acidic, RhoGEF (also called Dbl-homologous or DH), Pleckstrin Homology (PH), C1 (zinc finger), SH2, and two SH3 domains. The SH3 domain of VAV is involved in the localization of proteins to specific sites within the cell, by interacting with proline-rich sequences within target proteins [, , ].This entry represents the second SH3 domain of VAV2.
VAV2 is widely expressed and functions as a guanine nucleotide exchange factor (GEF) for RhoA, RhoB and RhoG and also activates Rac1 and Cdc42 []. It is implicated in many cellular and physiological functions including blood pressure control, eye development, neurite outgrowth and branching, EGFR endocytosis and degradation, and cell cluster morphology, among others [, , , , ]. It has been reported to associate with Nek3. VAV proteins contain several domains that enable their function: N-terminal calponin homology (CH), acidic, RhoGEF (also called Dbl-homologous or DH), Pleckstrin Homology (PH), C1 (zinc finger), SH2, and two SH3 domains. The SH3 domain of VAV is involved in the localization of proteins to specific sites within the cell, by interacting with proline-rich sequences within target proteins [, , ].This entry represents the first SH3 domain of VAV2.
Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction []. It plays a role in clathrin-coated pit (CCP) formation []. It binds to many proteins through its multidomain structure and facilitates the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation []. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. This entry represents the first SH3 domain of ITSN2.
Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction []. It plays a role in clathrin-coated pit(CCP) formation []. It binds to many proteins through its multidomain structure and facilitates the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation []. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. This entry represents the second SH3 domain of ITSN2.
Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction []. It plays a role in clathrin-coated pit (CCP) formation []. It binds to many proteins through its multidomain structure and facilitates the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation []. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. This entry represents the third SH3 domain of ITSN2.
Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction []. It plays a role in clathrin-coated pit (CCP) formation []. It binds to many proteins through its multidomain structure and facilitates the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation []. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. This entry represents the fourth SH3 domain of ITSN2.
Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction []. It plays a role in clathrin-coated pit (CCP) formation []. It binds to many proteins through its multidomain structure and facilitates the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation []. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. This entry represents the fifth SH3 domain of ITSN2.
Beta-PIX, also called Rho guanine nucleotide exchange factor 7 (ARHGEF7) or Cool (Cloned out of Library)-1, activates small GTPases by exchanging bound GDP for free GTP. It acts as a GEF for both Cdc42 and Rac1 [], and plays important roles in regulating neuroendocrine exocytosis, focal adhesion maturation, cell migration, synaptic vesicle localization, and insulin secretion [, , , ].PIX proteins contain an N-terminal SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains, and a C-terminal leucine-zipper domain for dimerization. The SH3 domain of PIX binds to an atypical PxxxPR motif in p21-activated kinases (PAKs) with high affinity. The binding of PAKs to PIX facilitate the localization of PAKs to focal complexes and also localizes PAKs to PIX targets Cdc43 and Rac, leading to the activation of PAKs [, ].This entry represents the SH3 domain of beta-PIX.
PAK2 plays a role in pro-apoptotic signaling. It is cleaved and activated by caspases leading to morphological changes during apoptosis []. PAK2 is also activated in response to a variety of stresses including DNA damage, hyperosmolarity, serum starvation, and contact inhibition, and may play a role in coordinating the stress response []. PAK2 also contributes to cancer cell invasion through a mechanism distinct from that of PAK1 []. PAK2 belongs to the group I PAKs.Group I PAKs contain a PBD (p21-binding domain) overlapping with an AID (autoinhibitory domain), a C-terminal catalytic domain, SH3 binding sites and a non-classical SH3 binding site for PIX (PAK-interacting exchange factor). PAKs are Rho family GTPase-regulated kinases that serve as important mediators in the function of Cdc42 (cell division cycle 42) and Rac [].
PAK6 may play a role in stress responses through its activation by the mitogen-activated protein kinase (MAPK) p38 and MAPK kinase 6 (MKK6) pathway []. PAK6 is highly expressed in the brain. It is not required for viability, but together with PAK5, it is required for normal levels of locomotion and activity, and for learning and memory []. Increased expression of PAK6 is found in primary and metastatic prostate cancer [].PAK6 belongs to the group II PAKs, which contain a PBD (p21-binding domain) and a C-terminal catalytic domain, but do not harbor an AID (autoinhibitory domain) or SH3 binding sites []. PAKs are Rho family GTPase-regulated kinases that serve as important mediators in the function of Cdc42 (cell division cycle 42) and Rac [].
Abr (active breakpoint cluster region-related protein) and Bcr (breakpoint cluster region protein) are homologous proteins containing a C-terminal domain with GTPase-activating protein (GAP) activity specific for Rac. They control multiple cellular functions of murine macrophages []. They contain several domains, including tandem DH-PH, C2 and GAP domains. Bcr has an extra N-terminal oligomerization domain []. Bcr has been shown to fused to Abl tyrosine kinase in leukemia. The fusion of Bcr to Abl deregulates the tyrosine kinase activity of Abl []. The N-terminal oligomerization domain is thought to be the most critical component that allows the formation of homo-tetramer Bcr/Abl complexes and deregulates the Abl tyrosine kinase [, ]. The GTPase-activating activity of Bcr has been shown to be regulated by transglutaminase 2 (TG2), a multifunctional protein that has been implicated in numerous pathologies including that of neurodegeneration and celiac disease [, ].Abr is a critical regulator of Rho and Cdc42 during the single cell wound healing [].
Rho GTPase-activating protein 26 (ARHGAP26), also known as GTPase regulator associated with focal adhesion kinase (GRAF), is a GTPase-activating protein for the small GTPases of the Rho family RhoA and CDC42 [, ]. GRAF influences cytoskeletal changes mediated by Rho proteins []. It is recognised as a tumor suppressor []. GRAF contains an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, a Rho GAP domain, and a C-terminal SH3 domain. The SH3 domain of GRAF binds PKNbeta, a target of the small GTPase Rho [].This entry represents the BAR domain of GRAF. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions. The BAR domain of GRAF directly interacts with its Rho GAP domain and inhibits its activity. Autoinhibited GRAF is capable of binding membranes and tubulating liposomes, showing that the membrane-tubulation and GAP-inhibitory functions of the BAR domain can occur simultaneously [].
NDE-like 1 (NDEL1/NUDEL) and its paralogue, NDE, are involved in mitosis and neurodevelopment that have been implicated in psychiatric and neurodevelopmental disorders. NDEL1 contains the N-terminal LIS1-binding domain that stimulates the movement of dynein and the C-terminal domain that causes dynein-microtubule dissociation [, , ]. It can also bind the motor domain of dynein in its heavy-chain []. It has been shown to affect many aspects of dynein function, such as transport along the microtubule network of vesicles and lysosomes, with effects on the correct structure of the Golgi apparatus, as well as on the transport of intermediate filament proteins, short microtubules and viral glycoproteins. Its phosphorilation by Aurora-A kinase is essential for centrosomal separation and mitotic entry []. It also facilitates neurofilament polymerization, promotes axonal regeneration, regulates Cdc42 at the leading edge of migrating neurons and the GTPase activity of the microtubule remodeling protein Dynamin 2, etc [, ].
The type III secretion system of Gram-negative bacteria is used to transport virulence factors from the pathogen directly into the host cell []and is only triggered when the bacterium comes into close contact with the host. Effector proteins secreted by the type III system do not possess a secretion signal, and are considered unique because of this. Salmonella spp. secrete an effector protein called SopE that is responsible for stimulating the reorganisation of the host cell actin cytoskeleton, and ruffling of the cellular membrane []. It acts as a guanyl-nucleotide-exchange factor on Rho-GTPase proteins such as Cdc42 and Rac. As it is imperative for the bacterium to revert the cell back to its "normal"state as quickly as possible, another tyrosine phosphatase effector called SptP reverses the actions brought about by SopE [].Recently, it has been found that SopE and its protein homologue SopE2 can activate different sets of Rho-GTPases in the host cell []. Far from being a redundant set of two similar type III effectors, they both act in unison to specifically activate different Rho-GTPase signalling cascades in the host cell during infection.This entry represents the N-terminal domain of SopE and SopE2. The function of this domain is unknown.
The type III secretion system of Gram-negative bacteria is used to transport virulence factors from the pathogen directly into the host cell []and is only triggered when the bacterium comes into close contact with the host. Effector proteins secreted by the type III system do not possess a secretion signal, and are considered unique because of this. Salmonella spp. secrete an effector protein called SopE that is responsible for stimulating the reorganisation of the host cell actin cytoskeleton, and ruffling of the cellular membrane []. It acts as a guanyl-nucleotide-exchange factor on Rho-GTPase proteins such as Cdc42 and Rac. As it is imperative for the bacterium to revert the cell back to its "normal"state as quickly as possible, another tyrosine phosphatase effector called SptP reverses the actions brought about by SopE []. Recently, it has been found that SopE and its protein homologue SopE2 can activate different sets of Rho-GTPases in the host cell []. Far from being a redundant set of two similar type III effectors, they both act in unison to specifically activate different Rho-GTPase signalling cascades in the host cell during infection.This entry represents the guanine nucleotide exchange factor domain of SopE. This domain has an α-helical structure consisting of two three-helix bundles arranged in a lamdba shape [, ].
OCRL1 hydrolyzes phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P2) and the signaling molecule phosphatidylinositol 1,4,5-trisphosphate (PtIns(1,4,5)P3), and thereby modulates cellular signaling events []. OCRL1 resides on vesicular structures throughout the endosomal system and the Golgi complex, and is also present at the plasma membrane in membrane ruffles and at late-stage endocytic clathrin-coated pits. It binds clathrin, clathrin adaptors, several GTPases, and the endocytic proteins APPL1 and Ses1/2 []. Mutations in the OCRL1 gene cause Lowe Syndrome, leading to cataracts, mental retardation and renal failure []. Mutations in OCRL can also give rise to a milder pathology, Dent disease 2, which is characterised by renal Fanconi syndrome in the absence of extrarenal pathologies [].OCRL1 shares ~45% sequence identity with INPP5B and has the same domain organization. However, a loop in the Rho GAP domain contains a second clathrin box which is absent in INPP5B. INPP5B shares most interacting partners with OCRL, except for clathrin and the endocytic clathrin adaptor AP-2 []. OCRL1 contains a PH domain, a 5-phosphatase domain, an ASH domain and a Rho-GAP domain. The RhoGAP domain lacks the catalytic arginine and is catalytically inactive. However, the RhoGAP domain of OCRL interacts with Rac and Cdc42, but only the Cdc42 interaction is GTP-dependent. The RhoGAP domain also interacts with three endocytic proteins containing the F&H motif: APPL1, Ses1 and Ses2. OCRL1 interacts with Rab GTPase (Rab8) through its ASH domain []. This entry represents the inositol polyphosphate 5-phosphatase (INPP5c) domain of OCRL1/INPP5B.
This entry represents a conserved region within a number of eukaryotic dedicator of cytokinesis proteins (DOCK), which are guanine nucleotide exchange factors (GEFs) [, , ], that activate some small GTPases by exchanging bound GDP for free GTP such as Rac. DOCK proteins are required during several cellular processes, such as cell motility and phagocytosis []. These proteins have a DOCK-homology region 1 (DHR-1, also known as DOCK-type C2 domain) at the N-terminal and a DHR-2 (also known as DOCKER domain) at the C-terminal. The DOCKER domain () is a GEF catalytic domain organised into three lobes, A, B and C, with the Rho-family binding site and catalytic centre generated entirely from lobes B and C. This entry represents Lobe B, which adopts an unusual architecture of two antiparallel beta sheets disposed in a loosely packed orthogonal arrangement. This lobe changes its position relative to lobe C and the bound GTPase, which suggests that lobe B distinguishes between the switch 1 conformations of the small GTPases Rac1 and Cdc42 [, ].
The type III secretion system of Gram-negative bacteria is used to transport virulence factors from the pathogen directly into the host cell []and is only triggered when the bacterium comes into close contact with the host. Effector proteins secreted by the type III system do not possess a secretion signal, and are considered unique because of this. Salmonella spp. secrete an effector protein called SopE that is responsible for stimulating the reorganisation of the host cell actin cytoskeleton, and ruffling of the cellular membrane []. It acts as a guanyl-nucleotide-exchange factor on Rho-GTPase proteins such as Cdc42 and Rac. As it is imperative for the bacterium to revert the cell back to its "normal"state as quickly as possible, another tyrosine phosphatase effector called SptP reverses the actions brought about by SopE []. SopE and its protein homologue SopE2 canactivate different sets of Rho-GTPases in the host cell []. Far from being a redundant set of two similar type III effectors, they both act in unison to specifically activate different Rho-GTPase signalling cascades in thehost cell during infection.
RhoG is a GTPase with high sequence similarity to members of the Rac subfamily, including the regions involved in effector recognition and binding. However, RhoG does not bind to known Rac1 and Cdc42 effectors, including proteins containing a Cdc42/Rac interacting binding (CRIB) motif. Instead, RhoG interacts directly with Elmo, an upstream regulator of Rac1, in a GTP-dependent manner and forms a ternary complex with Dock180 to induce activation of Rac1 []. The RhoG-Elmo-Dock180 pathway is required for activation of Rac1 and cell spreading mediated by integrin, as well as for neurite outgrowth induced by nerve growth factor. Thus RhoG activates Rac1 through Elmo and Dock180 to control cell morphology []. RhoG has also been shown to play a role in caveolar trafficking []and has a novel role in signaling the neutrophil respiratory burst stimulated by G protein-coupled receptor (GPCR) agonists []. Most Rho proteins contain a lipid modification site at the C terminus, with a typical sequence motif CaaX, where a = an aliphatic amino acid and X = any amino acid. Lipid binding is essential for membrane attachment, a key feature of most Rho proteins.
This entry represents the Actin nucleation-promoting factor WAS (WASP). The WASP proteins signal to the cytoskeleton through the Arp2/3 complex, an actin-nucleating assembly that regulates the structure and dynamics of actin filament networks at the leading edge of the cell []. The activity of WASP can be regulated by the Rho-family GTPase, Cdc42 []. Mutations in WASP lead to the Wiskott-Aldrich syndrome, a paediatric disorder characterised by actin cytoskeletal defects in haematopoietic cells, leading clinically to thrombocytopenia, eczema and immunodeficiency [].Similar to mammalian WASP proteins, Wsp1 and Las17 also has a role in regulating actin assembly [, ]. In Saccharomyces cerevisiae, Las17 is the primary activator of Arp2/3-driven actin nucleation and is required for membrane invagination during endocytosis []. Las17 can also nucleate actin filaments independently of Arp2/3 through its polyproline domain [].WASP family members have unique N-terminal regions, followed by a central segment rich in proline, and a common C-terminal region. Their conserved C-terminal VCA domain consists of two WH2 (WASP homology 2) domains ("V"referring to either a single or multiple WH2 domains), followed by a connector domain ("C") and an acidic short extension ("A"). In the VCA region, the WH2 domain(s) bind G-actin, whereas the CA domain binds Arp2/3 complex []. Their distinct N-terminal region enables family members to activate Arp2/3 in response to differentupstream signals.
FCH domain is a short conserved region of around 60 amino acids first described as a region of homology between FER and CIP4 proteins []. In the CIP4 protein the FCH domain binds to microtubules []. The FCH domain is always found N-terminally and is followed by a coiled-coil region. The FCH and coiled-coil domains are structurally similar to Bin/amphiphysin/RVS (BAR) domains []. They are α-helical membrane-binding modules that function in endocytosis, regulation of the actin cytoskeleton and signalling []. Proteins containing an FCH domain can be divided in 3 classes []:A subfamily of protein kinases usually associated with an SH2 domain:Fps/fes (Fujimani poultry sarcoma/feline sarcoma) proto-oncogenes. They are non-receptor protein-tyrosine kinases preferentially expressed in myeloid lineage. The viral oncogene has an unregulated kinase activity which abrogates the need for cytokines and influences differentiation of haematopoietic progenitor cells.Fes related protein (fer). It is an ubiquitously expressed homologue of Fes.Adaptor proteins usually associated with a C-terminal SH3 domain:Schizosaccharomyces pombe CDC15 protein. It mediates cytoskeletal rearrangements required for cytokinesis. It is essential for viability.CD2 cytoplasmic domain binding protein.Mammalian Cdc42-interacting protein 4 (CIP4). It may act as a link between Cdc42 signaling and regulation of the actin cytoskeleton.Mammalian PACSIN proteins. A family of cytoplasmic phosphoproteins playing a role in vesicle formation and transport.A subfamily of Rho-GAP proteins:Mammalian RhoGAP4 proteins. They may down-regulate Rho-like GTPases in hematopoietic cells.Yeast RHO GTPase-activating protein RGD1 (also known as YBR260C).Caenorhabditis elegans hypothetical protein ZK669.1.
Based on sequence similarities a domain of homology has been identified in the following proteins [, ]:Citron and Citron kinase. These two proteins interact with the GTP-bound forms of the small GTPases Rho and Rac but not with Cdc42.Myotonic dystrophy kinase-related Cdc42-binding kinase (MRCKalpha). This serine/threonine kinase interacts with the GTP-bound form of the small GTPase Cdc42 and to a lesser extent with that of Rac.NCK Interacting Kinase (NIK), a serine/threonine protein kinase.ROM-1 and ROM-2, from yeast. These proteins are GDP/GTP exchange proteins (GEPs) for the small GTP binding protein Rho1.This domain, called the citron homology domain (CNH), is often found after cysteine rich and pleckstrin homology (PH) domains at the C-terminal end of a group of eukaryotic proteins. It is thought to act as a regulatory domain and could be involved in macromolecular interactions [, , , ]. Its structure has been solved in Rho guanyl nucleotide exchange factor (Rom2) from Neosartorya fumigata (Aspergillus fumigatus, ), where it shows a canonical β-propeller fold containing seven blades connected by small loops and arranged in a circular fashion [].
The I-BAR domain (also known as IMD domain, IRSp53 and MIM homology domain) is a BAR-like domain of approximately 250 amino acids found at the N-terminal in the IRSp53 (insulin receptor tyrosine kinase substrate p53) and in the evolutionarily related IRSp53/MIM family. The BAR domain forms an anti-parallel all-helical dimer, with a curved (banana-like) shape, that promotes membrane tubulation. The BAR domain containing proteins can be classified into three types: BAR, F-BAR and I-BAR. BAR and F-BAR proteins generate positive membrane curvature, while I-BAR proteins induce negative curvature [, ]. The I-BAR domain containing proteins include: Vertebrate MIM (missing in metastasis), an actin-binding scaffold protein that may be involved in cancer metastasis.Vertebrate ABBA, a MIM-related protein.Vertebrate insulin receptor tyrosine kinase substrate p53 (IRSp53), a multifunctional adaptor protein that links Rac1 with a Wiskott-Aldrich syndrome family verprolin-homologous protein 2 (WAVE2) to induce lamellipodia or Cdc42 with Mena to induce filopodia [].Vertebrate IRTKS.Vertebrate Pinkbar.Drosophila melanogaster (Fruit fly) CG32082-PA.Caenorhabditis elegans M04F3.5 protein.The vertebrate I-BAR family is divided into two major groups: the IRSp53/IRTKS/Pinkbar subfamily and the MIM/ABBA subfamily. The putative invertebrate homologues are positioned between them. The IRSp53/IRTKS/Pinkbar subfamily members contain a SH3 domain, and the MIM/ABBA subfamily proteins contain a WH2 (WASP-homology 2) domain. The vertebrate SH3-containing subfamily is further divided into three groups according to the presence or absence of the WWB and the half-CRIB motif [, ]. The BAR domain binds phosphoinositide-rich vesicles with high affinity and does not display strong actin filament binding/bundling activity [, ].
Sterile alpha motif (SAM) domains are known to be involved in diverse protein-protein interactions, associating with both SAM-containing and non-SAM-containing proteins pathway []. SAM domains exhibit a conserved structure, consisting of a 4-5-helical bundle of two orthogonally packed alpha-hairpins. However SAM domains display a diversity of function, being involved in interactions with proteins, DNA and RNA []. The name sterile alpha motif arose from its presence in proteins that are essential for yeast sexual differentiation. The SAM domain has had various names, including SPM, PTN (pointed), SEP (yeast sterility, Ets-related, PcG proteins), NCR (N-terminal conserved region) and HLH (helix-loop-helix) domain, all of which are related and can be classified as SAM domains.SAM domains occur in eukaryotic and in some bacterial proteins. Structures have been determined for several proteins that contain SAM domains, including Ets-1 transcription factor, which plays a role in the development and invasion of tumour cells by regulating the expression of matrix-degrading proteases []; Etv6 transcription factor, gene rearrangements of which have been demonstrated in several malignancies []; EphA4 receptor tyrosine kinase, which is believed to be important for the correct localization of a motoneuron pool to a specific position in the spinal cord []; EphB2 receptor, which is involved in spine morphogenesis via intersectin, Cdc42 and N-Wasp []; p73, a p53 homologue involved in neuronal development []; and polyhomeotic, which is a member of the Polycomb group of genes (Pc-G) required for the maintenance of the spatial expression pattern of homeotic genes [].
The type III secretion system of Gram-negative bacteria is used to transport virulence factors from the pathogen directly into the host cell []and is only triggered when the bacterium comes into close contact with the host. Effector proteins secreted by the type III system do not possess a secretion signal, and are considered unique because of this. Salmonella spp. secrete an effector protein called SopE that is responsible for stimulating the reorganisation of the host cell actin cytoskeleton, and ruffling of the cellular membrane []. It acts as a guanyl-nucleotide-exchange factor on Rho-GTPase proteins such as Cdc42 and Rac. As it is imperative for the bacterium to revert the cell back to its "normal"state as quickly as possible, another tyrosine phosphatase effector called SptP reverses the actions brought about by SopE []. Recently, it has been found that SopE and its protein homologue SopE2 can activate different sets of Rho-GTPases in the host cell []. Far from being a redundant set of two similar type III effectors, they both act in unison to specifically activate different Rho-GTPase signalling cascades in the host cell during infection.This entry represents the guanine nucleotide exchange factor domain of SopE and homologues. This domain has an α-helical structure consisting of two three-helix bundles arranged in a lamdba shape [, ].
OCRL1 hydrolyzes phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P2) and the signaling molecule phosphatidylinositol 1,4,5-trisphosphate (PtIns(1,4,5)P3), and thereby modulates cellular signaling events []. OCRL1 resides on vesicular structures throughout the endosomal system and the Golgi complex, and is also present at the plasma membrane in membrane ruffles and at late-stage endocytic clathrin-coated pits. It binds clathrin, clathrin adaptors, several GTPases, and the endocytic proteins APPL1 and Ses1/2 []. Mutations in the OCRL1 gene cause Lowe Syndrome, leading to cataracts, mental retardation and renal failure []. Mutations in OCRL can also give rise to a milder pathology, Dent disease 2, which is characterised by renal Fanconi syndrome in the absence of extrarenal pathologies [].OCRL1 shares ~45% sequence identity with INPP5B (not included in this entry) and has the same domain organization. However, a loop in the Rho GAP domain contains a second clathrin box which is absent in INPP5B. INPP5B shares most interacting partners with OCRL, except for clathrin and the endocytic clathrin adaptor AP-2 []. OCRL1 contains a PH domain, a 5-phosphatase domain, an ASH domain and a Rho-GAP domain. The RhoGAP domain lacks the catalytic arginine and is catalytically inactive. However, the RhoGAP domain of OCRL interacts with Rac and Cdc42, but only the Cdc42 interaction is GTP-dependent. The RhoGAP domain also interacts with three endocytic proteins containing the F&H motif: APPL1, Ses1 and Ses2. OCRL1 interacts with Rab GTPase (Rab8) through its ASH domain []. This entry represents the PH domain of OCRL1 []. The PH domain connects to the 5-phosphatase domain, which has a Dnase I-like fold [].
Rho guanosine triphosphatases (GTPases) are critical regulators of cell motility, polarity, adhesion, cytoskeletal organisation, proliferation, geneexpression, and apoptosis. Conversion of these biomolecular switches to the activated GTP-bound state is controlled by two families of guanine nucleotide exchanges factors (GEFs). DH-PH proteins are a large group of Rho GEFs comprising a catalytic Dbl homology (DH) domain with anadjacent pleckstrin homology (PH) domain within the context of functionally diverse signalling modules. The evolutionarily distinct and smaller family of DOCK (dedicator of cytokinesis) or CDM (CED-5, DOCK1180, Myoblast city) proteins activate either Rac or Cdc42 to control cell migration, morphogenesis, and phagocytosis. DOCK proteins share the DOCK-type C2 domain (also termed the DOCK-homology region (DHR)-1 or CDM-zizimin homology 1 (CZH1) domain and the DOCKER domain (also termed the DHR-2 or CZH2 domain) [, , , , , , ].The DOCK-type C2 domain is located toward the N terminus []. The DOCKER domain is a GEF catalytic domain of ~400 residues situated within the C terminus. The structure of the DOCKER domain differs from that of other GEF catalytic domains. It is organised into three lobes of roughly equal size (lobes A, B, and C), with the Rho-family binding site and catalytic centre generated entirely from lobes B and C. Lobe A is formed from an antiparallel array of alpha helices. Through extensive contacts with lobe B, lobe A stabilises the DHR2 domain. Lobe B adopts an unusual architecture of two antiparallel beta sheets disposed in a loosely packed orthogonal arrangement, whereas lobe C comprises a four-helix bundle [, ].This entry represents the DOCKER domain.
Rho guanosine triphosphatases (GTPases) are critical regulators of cell motility, polarity, adhesion, cytoskeletal organisation, proliferation, geneexpression, and apoptosis. Conversion of these biomolecular switches to the activated GTP-bound state is controlled by two families of guanine nucleotide exchanges factors (GEFs). DH-PH proteins are a large group of Rho GEFs comprising a catalytic Dbl homology (DH) domain with an adjacent pleckstrin homology (PH) domain within the context of functionally diverse signalling modules. The evolutionarily distinct andsmaller family of DOCK (dedicator of cytokinesis) or CDM (CED-5, DOCK1180, Myoblast city) proteins activate either Rac or Cdc42 to control cell migration, morphogenesis, and phagocytosis. DOCK proteins share the DOCK-type C2 domain (also termed the DOCK-homology region (DHR)-1 or CDM-zizimin homology 1 (CZH1) domain and the DHR-2 domain (also termed the CZH2 or DOCKER domain), [, , , , , ].The ~200 residue DOCK-type C2 domain is located toward the N terminus. It adopts a C2-like architecture and interacts with phosphatidylinositol3,4,5-trisphosphate []to mediate signalling and membrane localization. The central core of the DOCK-type C2 domain domain adopts an antiparallel β-sandwich with the "type II"C2 domain fold (a circular permutation of the more common "type I"topology), in which two 4-stranded sheets with strand order 6-5-2-3 and 7-8-1-4 create convex- and concave-exposed faces, respectively [].Some DOCK proteins are listed below:Mammalian Mammalian dedicator of cytokinesis 180 (DOCK180 or DOCK1),important for cell migration.Mammalian DOCK2, important for lymphocyte development, homong, activation,adhesion, polarization and migration processes.Mammalian DOCK3 (also known as MOCA), is expressed predominantly in neuronsand resides in growth cones and membrane ruffles.Mammalian DOCK4, possesses tumor suppressor properties.Mammalian DOCK9 (zizimin1), plays an important role in dendrite growth inhippocampal neurons through activation of Cdc42.Drosophila melanogaster Myoblast city.Caenorhabditis elegans CED-5.
All eukaryotic cells are surrounded by a plasma membrane, and they alsocontain multiple membrane-based organelles and structures inside cells. Thusmembrane remodeling is likely to be important for most cellular activities anddevelopment. The Bin-Amphiphysin-Rvs (BAR) domain superfamily of proteins hasbeen found to play a major role in remodeling cellular membranes linked withorganelle biogenesis, membrane trafficking, cell division, cell morphology andcell migration. The BAR domain superfamily of proteins is evolutionarilyconserved with representative members present from yeast to man. Currentlythere are three distinct families of BAR domain proteins: classical BAR, F-BAR (FCH-BAR e.g., Fes/CIP4 homology BAR e.g., Toca-1) and I-BAR (inverse-BAR e.g., IRSp53). The classical BAR, F-BAR, and I-BAR domainsare structurally similar homodimeric modules with antiparallel arrangement ofmonomers [, ].The F-BAR domain is emerging as an important player in membrane remodelingpathways. F-BAR domain proteins couple membrane remodeling with actin dynamicsassociated with endocytic pathways and filopodium formation. F-BAR domaincontaining proteins can be categorized into five sub-families based on theirphylogeny which is consistent with the additional protein domains theypossess, for example, RhoGAP domains, Cdc42 binding sites,SH2 domains, SH3 domains and tyrosinekinase domains [].The N-terminal part (about one third) of the F-BAR domain was previouslycharacterised as an FCH (FER-CIP4 homology) domain. However, the region ofsequence similarity extends to an adjacent region with a coiled-coil (CC)structure. Hence, the F-BAR domain (FCH+CC, ~300 amino acids) has also beencalled extended FC (EFC) domain. The F-BAR domain plays a role in dimerizationand membrane phospholipid binding. It binds specifically to certain kinds oflipids and acts as a a dimeric membrane-binding curvature effector [, , ].The F-BAR domain is composed of five helices. Its structure is composed of ashort N-terminal helix, three long α-helices, and a short C-terminal helixfollowed by an extended peptide of 17 amino acids [, ].
MLKs 1, 2, and 3 are Serine/Threonine Kinases (STKs), catalyzing the transfer of the gamma-phosphoryl group from ATP to S/T residues on protein substrates. MLKs act as mitogen-activated protein kinase kinase kinases (MAP3Ks, MKKKs, MAPKKKs), which phosphorylate and activate MAPK kinases (MAPKKs or MKKs or MAP2Ks), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals [, ]. MLKs play roles in immunity and inflammation, as well as in cell death, proliferation, and cell cycle regulation [, ]. Little is known about the specific function of MLK1, also called MAP3K9. It is capable of activating the c-Jun N-terminal kinase pathway []. Mice lacking both MLK1 and MLK2 are viable, fertile, and have normal life spans []. MLK2, also called MAP3K10, is abundant in brain, skeletal muscle, and testis. It functions upstream of the MAPK, c-Jun N-terminal kinase. It binds hippocalcin, a calcium-sensor protein that protects neurons against calcium-induced cell death. Both MLK2 and hippocalcin may be associated with the pathogenesis of Parkinson's disease []. MLK3, also called MAP3K11, is highly expressed in breast cancer cells and its signaling through c-Jun N-terminal kinase has been implicated in the migration, invasion, and malignancy of cancer cells []. It also functions as a negative regulator of Inhibitor of Nuclear Factor-KappaB Kinase (IKK) and thus impacts inflammation and immunity []. MLKs contain an SH3 domain, a catalytic kinase domain, a leucine zipper, a proline-rich region, and a CRIB domain that mediates binding to GTP-bound Cdc42 and Rac.This entry represents the SH3 domains of MLKs.
Small GTPases form an independent superfamily within the larger class of regulatory GTP hydrolases. This superfamily contains proteins that control a vast number of important processes and possess a common, structurally preserved GTP-binding domain [, ]. Sequence comparisons of small G proteins from various species have revealed that they are conserved in primary structures at the level of 30-55% similarity [].Crystallographic analysis of various small G proteins revealed the presence of a 20kDa catalytic domain that is unique for the whole superfamily [, ]. The domain is built of five alpha helices (A1-A5),six β-strands (B1-B6) and five polypeptide loops (G1-G5). A structural comparison of the GTP- and GDP-bound form, allows one to distinguish two functional loop regions: switch I and switch II that surround the gamma-phosphate group of the nucleotide. The G1 loop (also called the P-loop) that connects the B1 strand and the A1 helix is responsible for the binding of the phosphate groups. The G3 loop provides residues for Mg2 and phosphate binding and is located at the N terminus of the A2 helix. The G1 and G3 loops are sequentially similar to Walker A and Walker B boxes that are found in other nucleotide binding motifs. The G2 loop connects the A1 helix and the B2 strand and contains a conserved Thr residue responsible for Mg2 binding. The guanine base is recognised by the G4 and G5 loops. The consensus sequence NKXD of the G4 loop contains Lys and Asp residues directly interacting with the nucleotide. Part of the G5 loop located between B6 and A5 acts as a recognition site for the guanine base [].The small GTPase superfamily can be divided into at least 8 different families, including:Arf small GTPases. GTP-binding proteins involved in protein trafficking by modulating vesicle budding and uncoating within the Golgi apparatus.Ran small GTPases. GTP-binding proteins involved in nucleocytoplasmic transport. Required for the import of proteins into the nucleus and also for RNA export.Rab small GTPases. GTP-binding proteins involved in vesicular traffic.Rho small GTPases. GTP-binding proteins that control cytoskeleton reorganisation.Ras small GTPases. GTP-binding proteins involved in signalling pathways.Sar1 small GTPases. Small GTPase component of the coat protein complex II (COPII) which promotes the formation of transport vesicles from the endoplasmic reticulum (ER).Mitochondrial Rho (Miro). Small GTPase domain found in mitochondrial proteins involved in mitochondrial trafficking.Roc small GTPases domain. Small GTPase domain always found associated with the COR domain.This entry represents the Rho subfamily of Ras-like small GTPases. The small GTPase-like protein LIP2 (light insensitive period 2) from Arabidopsis thalianais implicated in control of the plant circadian rhythm []. The crystal structures of a number of the members of this entry have been determined: Rnd3/RhoE [], RhoA []and Cdc42 [].
The Rho family GTPases Rho, Rac and CDC42 regulate a diverse array of cellular processes. Like all members of the Ras superfamily, the Rho proteins cycle between active GTP-bound and inactive GDP-bound conformational states.Activation of Rho proteins through release of bound GDP and subsequentbinding of GTP, is catalysed by guanine nucleotide exchange factors (GEFs) inthe Dbl family. The proteins encoded by members of the Dbl family share acommon domain, presented in this entry, of about 200 residues (designated the Dbl homology or DH domain) that has been shown to encode a GEF activity specific for a number of Rho family members. In addition, all family members possess a second, shared domain designated the pleckstrin homology (PH) domain (). Trio and its homologue UNC-73 are unique within the Dbl family insomuch as they encode two distinct DH/PH domain modules. The PH domain is invariably located immediately C-terminal to the DH domain and this invariant topography suggests a functional interdependence between these two structural modules. Biochemical data have established the role of the conserved DH domain in Rho GTPase interaction and activation, and the role of the tandem PH domain in intracellular targeting and/or regulation of DH domain function. The DH domain of Dbl has been shown to mediate oligomerisation that is mostly homophilic in nature. In addition to the tandem DH/PH domains Dbl family GEFs contain diverse structural motifs like serine/threonine kinase, RBD, PDZ, RGS, IQ, REM, Cdc25, RasGEF, CH, SH2, SH3, EF, spectrin or Ig.The DH domain is composed of three structurally conserved regions separated bymore variable regions. It does not share significant sequence homology withother subtypes of small G-protein GEF motifs such as the Cdc25 domain and theSec7 domain, which specifically interact with Ras and ARF family small GTPases, respectively, nor with other Rho protein interactive motifs, indicating that the Dbl family proteins are evolutionarily unique. The DH domain is composed of 11 alpha helices that are folded into a flattened, elongated α-helix bundle in which two of the three conserved regions, conserved region 1 (CR1) and conserved region 3 (CR3), are exposed near the centre of one surface. CR1 and CR3, together with a part of alpha-6 and the DH/PH junction site, constitute the Rho GTPase interacting pocket.
This entry represents the N-terminal PH domain of FGD1.In general, FGDs (including FGD1, FGD2, FGD3 and FGD4/Frabin) have a RhoGEF (DH) domain, followed by an N-terminal PH domain, a FYVE domain and a C-terminal PH domain. All FGDs are guanine nucleotide exchange factors that activates the Rho GTPase Cdc42, an important regulator of membrane trafficking. The RhoGEF domain is responsible for GEF catalytic activity, while the N-terminal PH domain is involved in intracellular targeting of the DH domain []. Mutations in the FGD1 gene are responsible for the X-linked disorder known as faciogenital dysplasia (FGDY) []. Both FGD1 and FGD3 are targeted by the ubiquitin ligase SCF(FWD1/beta-TrCP) upon phosphorylation of two serine residues in its DSGIDS motif and subsequently degraded by the proteasome. However, FGD1 and FGD3 induced significantly different morphological changes in HeLa Tet-Off cells and while FGD1 induced long finger-like protrusions, FGD3 induced broad sheet-like protrusions when the level of GTP-bound Cdc42 was significantly increased by the inducible expression of FGD3. They also reciprocally regulated cell motility in inducibly expressed in HeLa Tet-Off cells, FGD1 stimulated cell migration while FGD3 inhibited it. FGD1 and FGD3 therefore play different roles to regulate cellular functions, even though their intracellular levels are tightly controlled by the same destruction pathway through SCF(FWD1/beta-TrCP) [, ].PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner []. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity []. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane []. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes [].
This entry represents the C-terminal PH domain of FGD1-4.In general, FGDs (including FGD1, FGD2, FGD3 and FGD4/Frabin) have a RhoGEF (DH) domain, followed by an N-terminal PH domain, a FYVE domain and a C-terminal PH domain. All FGDs are guanine nucleotide exchange factors that activates the Rho GTPase Cdc42, an important regulatorof membrane trafficking. The RhoGEF domain is responsible for GEF catalytic activity, while the N-terminal PH domain is involved in intracellular targeting of the DH domain []. Mutations in the FGD1 gene are responsible for the X-linked disorder known as faciogenital dysplasia (FGDY) []. Both FGD1 and FGD3 are targeted by the ubiquitin ligase SCF(FWD1/beta-TrCP) upon phosphorylation of two serine residues in its DSGIDS motif and subsequently degraded by the proteasome. However, FGD1 and FGD3 induced significantly different morphological changes in HeLa Tet-Off cells and while FGD1 induced long finger-like protrusions, FGD3 induced broad sheet-like protrusions when the level of GTP-bound Cdc42 was significantly increased by the inducible expression of FGD3. They also reciprocally regulated cell motility in inducibly expressed in HeLa Tet-Off cells, FGD1 stimulated cell migration while FGD3 inhibited it. FGD1 and FGD3 therefore play different roles to regulate cellular functions, even though their intracellular levels are tightly controlled by the same destruction pathway through SCF(FWD1/beta-TrCP) [, ].PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner []. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity []. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane []. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes [].
