This entry represents the Ran-binding domain (RBD) found in RanBP1 from humans and Yrb1 from budding yeasts. RanBP1 and Yrb1 are involved in nuclear import and export. RanBP1 and Yrb1 have been shown to shuttle between the nucleus and cytoplasm and the conserved RBD is necessary and sufficient for the essential function and nucleocytoplasmic shuttling []. RanBP1/Yrb1 acts as a negative regulator of Regulator of chromosome condensation 1 (RCC1) by inhibiting RCC1-stimulated guanine nucleotide release from Ran [].
Ran is an evolutionary conserved member of the Ras superfamily that regulates all receptor-mediated transport between the nucleus and the cytoplasm. Ran Binding Protein 1 (RanBP1) has guanine nucleotide dissociation inhibitory activity, specific for the GTP form of Ran and also functions to stimulate Ran GTPase activating protein(GAP)-mediated GTP hydrolysis by Ran. RanBP1 contributes to maintaining the gradient of RanGTP across the nuclear envelope high (GDI activity) or the cytoplasmic levels of RanGTP low (GAP cofactor) [].All RanBP1 proteins contain an approx 150 amino acid residue Ran binding domain. Ran BP1 binds directly to RanGTP with high affinity.There are four sites of contact between Ran and the Ran binding domain. One of these involves binding of the C-terminal segment of Ran to a groove on the Ran binding domain that is analogous to the surface utilised in the EVH1-peptide interaction []. Nup358 contains four Ran binding domains. The structure of the first of these is known [].
This entry represents a group of RanGTP-binding proteins that contain a conserved RanGTP-binding motif, also called a Ran-binding domain (RBD). They have been implicated in nucleocytoplasmic transport. NUP358 (RanBP2) is localised to the cytoplasmic filaments protruding from the nuclear pore complex (NPC) into the cytoplasm, while RanBP3/Hba1 are localised to the nucleoplasm and Nup2 is localised to the NPC. In general, RanBP1 and other members of this protein family increase, via their conserved RBDs, the rate of RanGAP1-mediated GTP hydrolysis on Ran [].
The small Ras-like GTPase Ran plays an essential role in the transport of macromolecules in and out of the nucleus and has been implicated in spindle and nuclear envelope formation during mitosis in higher eukaryotes. The Saccharomyces cerevisiae ORF YGL164c encoding a novel RanGTP-binding protein, termed Yrb30p was identified. The protein competes with S. cerevisiae RanBP1 (Yrb1p) for binding to the GTP-bound form of S. cerevisiae Ran (Gsp1p) and is, like Yrb1p, able to form trimeric complexes with RanGTP and some of the karyopherins [].
Ran GTPase is a ubiquitous protein required for nuclear transport, spindle assembly, nuclear assembly and mitotic cell cycle regulation. RanGTPase activating protein 1 (RanGAP1) is one of several RanGTPase accessory proteins. During interphase, RanGAP1 is located in the cytoplasm, while during mitosis it becomes associated with the kinetochores []. Cytoplasmic RanGAP1 is required for RanGTPase-directed nuclear transport. The activity of RanGAP1 requires the accessory protein RanBP1. RanBP1 facilitates RanGAP1 hydrolysis of Ran-GTP, both directly and by promoting the dissociation of Ran-GTP from transport receptors, which would otherwise block RanGAP1-mediated hydrolysis. RanGAP1 is thought to bind to the Switch 1 and Switch 2 regions of RanGTPase. The Switch 2 region can be buried in complexes with karyopherin-beta2, and requires the interaction with RanBP1 to permit RanGAP1 function. RanGAP1 can undergo SUMO (small ubiquitin-like modifier) modification, which targets RanGAP1 to RanBP2/Nup358 in the nuclear pore complex, and is required for association with the nuclear pore complex and for nuclear transport []. The enzymes involved in SUMO modification are located on the filaments of the nuclear pore complex.The RanGAP1 N-terminal domain is fairly well conserved between vertebrate and fungal proteins, but yeast does not contain the C-terminal domain. The C-terminal domain is SUMO-modified and required for the localisation of RanGAP1 at the nuclear pore complex. The structure of the C-terminal domain is multihelical, consisting of two curved alpha/alpha layers in a right-handed superhelix.
Ran GTPase is a ubiquitous protein required for nuclear transport, spindle assembly, nuclear assembly and mitotic cell cycle regulation. RanGTPase activating protein 1 (RanGAP1) is one of several RanGTPase accessory proteins. During interphase, RanGAP1 is located in the cytoplasm, while during mitosis it becomes associated with the kinetochores []. Cytoplasmic RanGAP1 is required for RanGTPase-directed nuclear transport. The activity of RanGAP1 requires the accessory protein RanBP1. RanBP1 facilitates RanGAP1 hydrolysis of Ran-GTP, both directly and by promoting the dissociation of Ran-GTP from transport receptors, which would otherwise block RanGAP1-mediated hydrolysis. RanGAP1 is thought to bind to the Switch 1 and Switch 2 regions of RanGTPase. The Switch 2 region can be buried in complexes with karyopherin-beta2, and requires the interaction with RanBP1 to permit RanGAP1 function. RanGAP1 can undergo SUMO (small ubiquitin-like modifier) modification, which targets RanGAP1 to RanBP2/Nup358 in the nuclear pore complex, and is required for association with the nuclear pore complex and for nuclear transport []. The enzymes involved in SUMO modification are located on the filaments of the nuclear pore complex.The RanGAP1 N-terminal domain is fairly well conserved between vertebrate and fungal proteins, but yeast does not contain the C-terminal domain. The C-terminal domain is SUMO-modified and required for the localisation of RanGAP1 at the nuclear pore complex. The structure of the C-terminal domain is multihelical, consisting of two curved alpha/alpha layers in a right-handed superhelix.
Pleckstrin homology (PH) domains are small modular domains that occur in a large variety of signalling proteins, where they serve as simple targeting domains that bind lipids [, , ]. PH domains have a partly opened β-barrel topology that is capped by an alpha helix. The structure of PH domains is similar to the phosphotyrosine-binding domain (PTB) found in IRS-1 (insulin receptor substrate 1) [], Shc adaptor and Numb []; to the Ran-binding domain, found in Nup nuclear pore complex and Ranbp1 []; to the Enabled/VASP homology domain 1 (EVH1 domain), found in Enabled, VASP (vasodilator-stimulated phosphoprotein), Homer and WASP actin regulatory protein []; and to the third domain of FERM, found in moesin, radixin, ezrin, merlin and talin [].This superfamily represents the PH domain and structurally related domains.
The EVH1 (WH1, RanBP1-WASP) domain is found in multi-domain proteins implicated in a diverse range of signalling, nuclear transport and cytoskeletal events. This domain of around 115 amino acids is present in species ranging from yeast to mammals. Many EVH1-containing proteins associate with actin-based structures and play a role in cytoskeletal organisation. EVH1 domains recognise and bind the proline-rich motif FPPPP with low-affinity, further interactions then form between flanking residues [, ].WASP family proteins contain an EVH1 (WH1) in their N-terminals which bind proline-rich sequences in the WASP interacting protein. Proteins of the RanBP1 family contain a WH1 domain in their N-terminal region, which seems to bind a different sequence motif present in the C-terminal part of RanGTP protein [, ]. Tertiary structure of the WH1 domain of the Mena protein revealed structure similarities with the pleckstrin homology (PH) domain. The overall fold consists of a compact parallel β-sandwich, closed along one edge by a long α-helix. A highly conserved cluster of three surface-exposed aromatic side-chains forms the recognition site for the molecules target ligands. [].
The entry refers to the EVH1 domain found in WASP family proteins.The EVH1 (WH1, RanBP1-WASP) domain is found in multi-domain proteins implicated in a diverse range of signalling, nuclear transport and cytoskeletal events. This domain of around 115 amino acids is present in species ranging from yeast to mammals. Many EVH1-containing proteins associate with actin-based structures and play a role in cytoskeletal organisation. EVH1 domains recognise and bind the proline-rich motif FPPPP with low-affinity, further interactions then form between flanking residues [, ].WASP family proteins contain an EVH1 (WH1) in their N-terminals which bind proline-rich sequences in the WASP interacting protein. Proteins of the RanBP1 family contain a WH1 domain in their N-terminal region, which seems to bind a different sequence motif present in the C-terminal part of RanGTP protein [, ]. Tertiary structure of the WH1 domain of the Mena protein revealed structure similarities with the pleckstrin homology (PH) domain. The overall fold consists of a compact parallel β-sandwich, closed along one edge by a long α-helix. A highly conserved cluster of three surface-exposed aromatic side-chains forms the recognition site for the molecules target ligands. [].The actin nucleation-promoting factor WAS (WASP; also called Bee1p) and its homologue N (neuronal)-WASP are signal transduction proteins that promote actin polymerization in response to upstream intracellular signals []. Wiskott-Aldrich Syndrome (WAS) is an X-linked recessive disease, characterized by eczema, immunodeficiency, and thrombocytopenia []. The majority of patients with WAS, or a milder version of the disorder, X-linked thrombocytopenia (XLT), have point mutations in the EVH1 domain of WASP []. WASP is an actin regulatory protein consisting of an N-terminal EVH1 domain, a basic region (B), a GTP binding domain (GBP), a proline rich region, a WH2 domain, and a verprolin-cofilin-acidic motif (VCA) which activates the actin-related protein (Arp)2/3 actin nucleating complex []. The B, GBD, and the proline-rich region are involved in autoinhibitory interactions that repress or block the activity of the VCA. Yeast members lack the GTP binding domain. The EVH1 domains are part of the PH domain superfamily [].
