CDK5 regulatory subunit-associated protein 2 (CDK5RAP2) is a centrosomal protein that regulates centrosomal maturation by recruitment of a gamma-tubulin ring complex (gamma-TuRC) onto centrosomes []. It interacts directly with EB1, a prototypic member of microtubule plus-end tracking proteins. The CDK5RAP2-EB1 complex regulates microtubule dynamics and stability []. CDK5RAP2 also interacts with Cep169, a microtubule plus-end-tracking centrosomal protein; this interaction regulates stability of microtubules []. Mutations in the CDK5RAP2 gene cause microcephaly 3, primary, autosomal recessive (MCPH3) [, ].
CDK5RAP3 (also known as C53 or LZAP) serves as a probable tumour suppressor initially identified as a CDK5R1 interactor controllingcell proliferation [, ]. It negatively regulates NF-kappa-B-mediated gene transcription through the control of RELA phosphorylation [, ]. It also regulates mitotic G2/M transition checkpoint and mitotic G2 DNA damage checkpoint [, ]. It has been shown to bind Wip1 and stimulates its phosphatase activity [].
This group represents protein CABLES (CDK5 and ABL1 enzyme substrate), including CABLES1 and CABLES2 [, ]. CABLES1 is a cyclin-dependent kinase binding protein, primarily involved in cell cycle regulation []. CABLES1 binds to different functional domains of p53 and p73 and modifies their cell death-inducing activities []. It may be a tumour suppressor in human ovarian cancer []. CABLES2 is involved in both p53-mediated and p53-independent apoptotic pathways [].
Drebrin is an actin binding protein that plays a key role in actin organisation. The interaction between drebrin and microtubule-binding +TIP protein EB3 links dynamic microtubules to actin filaments and is required for neuritogenesis []. The F-actin-bundling activity of drebrin can be regulated by Cdk5 phosphorylation []. In mammals, drebrin is highly expressed in growth cones of developing neurons and in dendritic spines of mature neurons []. Loss of drebrin has been linked to memory loss in patients with Down syndrome/Alzheimer's [, ].
Cyclins are eukaryotic proteins that play an active role in controlling nuclear cell division cycles, and regulate cyclin dependent kinases (CDKs) [].Members of the cyclin-G subfamily of cyclins can associate with cdk5 and GAK. They also interact with the B' subclass of PP2A phosphatase and with Mdm2 and may regulate the p53-Mdm2 network []. In humans and other mammals, there are two cyclin-G subtypes - cyclin-G1 and cyclin-G2. Their expression is linked to cancer progression [, ]. This entry represents cyclin-G2 and cycling-G.
Cyclins are eukaryotic proteins that play an active role in controlling nuclear cell division cycles, and regulate cyclin dependent kinases (CDKs) [].Members of the cyclin-G subfamily of cyclins can associate with cdk5 and GAK. They also interact with the B' subclass of PP2A phosphatase and with Mdm2 and may regulate the p53-Mdm2 network []. In humans and other mammals, there are two cyclin-G subtypes - cyclin-G1 and cyclin-G2. Their expression is linked to cancer progression [, ]. This entry represents cyclin-G1.
Septin 5 (SEPT5) belongs to the septin family. Septin 5, also known as CDCrel-1, is predominantly expressed in the nervous system, co-localises with synaptic vesicles and is involved in exocytosis []. In humans, its role in exocytotic secretion that is modulated by Cdk5 phosphorylation [, ]. SEPT5 interacts with SEPT8 and SEPT11. The complex formed by SEPT5 and SEPT11 is involved in the exocytosis mechanism in human umbilical vein endothelial cells (HUVECs) [].Septins were first discovered in budding yeast as a major component of bud neck filaments during cell septation [, ]. Later, its homologues were identified in nearly all eukaryotes, including humans. They are all GTP-binding proteins that are involved in diverse cellular functions, including cell cycle progression, vesicle trafficking, cytokinesis, cell migration, membrane dynamics, and chromosome segregation [, ]. Similar to cytoskeleton components such as actins and tubulins, they can assemble into filaments and bundles. However, unlike actin filaments and microtubules, septin filaments are not polar, similarly to intermediate filaments []. The number of septin genes per organism is variable: S. cerevisiae has seven and humans have 13 (SEPT1-12 and SEPT14; SEPT13 is a pseudogene now called SEPT7P2) []. All septins can form heteromeric complexes, which associate to form higher-order structures, including filaments, rings and cage-like formations [, ].
The methylthiotransferase (MTTase) or miaB-like family is named after the (dimethylallyl)adenosine tRNA MTTase miaB protein, which catalyses a C-H to C-S bond conversion in the methylthiolation of tRNA. A related bacterial enzyme RimO performs a similar methylthiolation, but on a protein substrate. RimO acts on the ribosomal protein S12 and forms a separate MTTase subfamily. The miaB-subfamily includes mammalian CDK5 regulatory subunit-associated proteins and similar proteins in other eukaryotes. Two other subfamilies, yqeV and CDKAL1, are named after a Bacillus subtilis and a human protein, respectively. While yqeV-like proteins are found in bacteria, CDKAL1 subfamily members occur in eukaryotes and in archaebacteria [].The likely MTTases from these 4 subfamilies contain an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain (see ). The core forms a radical SAM fold (or AdoMet radical), containing a cysteine motif CxxxCxxC that binds a [4Fe-4S]cluster [, , ]. A reducing equivalent from the [4Fe-4S]+ cluster is used to cleave S-adenosylmethionine (SAM) to generate methionine and a 5'-deoxyadenosyl radical. The latter is thought to produce a reactive substrate radical that is amenable to sulphur insertion [, ]. The N-terminal MTTase domain contains 3 cysteines that bind a second [4Fe-4S]cluster, in addition to the radical-generating [4Fe-4S]cluster, which could be involved in the thiolation reaction. The C-terminal TRAM domain is not shared with other radical SAM proteins outside the MTTase family. The TRAM domain can bind to RNA substrate and seems to be important for substrate recognition. The tertiary structure of the central radical SAM fold has six beta/alpha motifs resembling a three-quarter TIM barrel core []. The N-terminal MTTase domain might form an additional [beta/alpha]2 TIM barrel unit [].
The methylthiotransferase (MTTase) or miaB-like family is named after the (dimethylallyl)adenosine tRNA MTTase miaB protein, which catalyses a C-H to C-S bond conversion in the methylthiolation of tRNA. A related bacterial enzyme rimO performs a similar methylthiolation, but on a protein substrate. RimO acts on the ribosomal protein S12 and forms a separate MTTase subfamily. The miaB-subfamily includes mammalian CDK5 regulatory subunit-associated proteins and similar proteins in other eukaryotes. Two other subfamilies, yqeV and CDKAL1, are named after a Bacillus subtilis and a human protein, respectively. While yqeV-like proteins are found in bacteria, CDKAL1 subfamily members occur in eukaryotes and in archaebacteria. The likely MTTases from these 4 subfamilies contain an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain (see ). The core forms a radical SAM fold (or AdoMet radical), containing a cysteine motif CxxxCxxC that binds a [4Fe-4S]cluster [, , ]. A reducing equivalent from the [4Fe-4S]+ cluster is used to cleave S-adenosylmethionine (SAM) to generate methionine and a 5'-deoxyadenosyl radical. The latter is thought to produce a reactive substrate radical that is amenable to sulphur insertion [, ]. The N-terminal MTTase domain contains 3 cysteines that bind a second [4Fe-4S]cluster, in addition to the radical-generating [4Fe-4S]cluster, which could be involved in the thiolation reaction. The C-terminal TRAM domain is not shared with other radical SAM proteins outside the MTTase family. The TRAM domain can bind to RNA substrate and seems to be important for substrate recognition. The tertiary structure of the central radical SAM fold has six beta/alpha motifs resembling a three-quarter TIM barrel core (see ) []. The N-terminal MTTase domain might form an additional [beta/alpha]2 TIM barrel unit [].
The methylthiotransferase (MTTase) or miaB-like family is named after the (dimethylallyl)adenosine tRNA MTTase miaB protein, which catalyses a C-H to C-S bond conversion in the methylthiolation of tRNA. A related bacterial enzyme rimO performs a similar methylthiolation, but on a protein substrate. RimO acts on the ribosomal protein S12 andforms a separate MTTase subfamily. The miaB-subfamily includes mammalian CDK5 regulatory subunit-associated proteins and similar proteins in other eukaryotes. Two other subfamilies, yqeV and CDKAL1, are named after a Bacillus subtilis and a human protein, respectively. While yqeV-like proteins are found in bacteria, CDKAL1 subfamily members occur in eukaryotes and in archaebacteria. The likely MTTases from these 4 subfamilies contain an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain (see ). The core forms a radical SAM fold (or AdoMet radical), containing a cysteine motif CxxxCxxC that binds a [4Fe-4S]cluster [, , ]. A reducing equivalent from the [4Fe-4S]+ cluster is used to cleave S-adenosylmethionine (SAM) to generate methionine and a 5'-deoxyadenosyl radical. The latter is thought to produce a reactive substrate radical that is amenable to sulphur insertion [, ]. The N-terminal MTTase domain contains 3 cysteines that bind a second [4Fe-4S]cluster, in addition to the radical-generating [4Fe-4S]cluster, which could be involved in the thiolation reaction. The C-terminal TRAM domain is not shared with other radical SAM proteins outside the MTTase family. The TRAM domain can bind to RNA substrate and seems to be important for substrate recognition. The tertiary structure of the central radical SAM fold has six beta/alpha motifs resembling a three-quarter TIM barrel core (see ) []. The N-terminal MTTase domain might form an additional [beta/alpha]2 TIM barrel unit []. This entry represents a conserved site containing three of the conserved cysteines that form the motif in the central radical SAM fold.
Amphiphysins belong to the expanding BAR (Bin-Amphiphysin-Rvsp) family proteins, all members of which share a highly conserved N-terminal BAR domain, which has predicted coiled-coil structures required for amphiphysin dimerisation and plasma membrane interaction []. Almost all members also share a conserved C-terminal Src homology 3 (SH3) domain, which mediates their interactions with the GTPase dynamin and the inositol-5'-phosphatase synaptojanin 1 in vertebrates and with actin in yeast. The central region of all these proteins is most variable. In mammals, the central region of amphiphysin I and amphiphysin IIa contains a proline-arginine-rich region for endophilin binding and a CLAP domain, for binding to clathrin and AP-2. The interactions mediated by both the central and C-terminal domains are believed to be modulated by protein phosphorylation [, ].Amphiphysins are proteins involved in clathrin-mediated endocytosis clathrin-mediated endocytosis, actin function, and signalling pathways [, ].Amphiphysin 1 was first identified in 1992 as a brain protein that was partially-associated with synaptic vesicles. Following its cloning, it was also realised to be a human auto-antigen that is detected in a rare neurological disease, Stiff-Man Syndrome, and also in certain types of cancer []. Amphiphysin 1 senses and facilitates membrane curvature to mediate synaptic vesicles invagination and fission during newly retrieved presynaptic vesicle formation and also acts as a linker protein binding with dynamin, clathrin, Amphiphysin II, and other dephosphins in the clathrin-coated complex. Amphiphysin 1 is cleaved an asparagine endopeptidase (AEP), which generates afragment that increases with aging. This fragment disrupts the normal endocytic function of Amphiphysin 1, leading to synaptic dysfunction, as it activates CDK5 inducing tau hyperphosphorylation. Therefore, Amphiphysin 1 posttranslational modification contributes to pathogenesis of Alzheimer's disease, being the AEP a therapeutic target [].
The methylthiotransferase (MTTase) or miaB-like family is named after the (dimethylallyl)adenosine tRNA MTTase miaB protein, which catalyses a C-H to C-S bond conversion in the methylthiolation of tRNA. A related bacterial enzyme rimO performs a similar methylthiolation, but on a protein substrate. RimO acts on the ribosomal protein S12 and forms a separate MTTase subfamily. The miaB-subfamily includes mammalian CDK5 regulatory subunit-associated proteins and similar proteins in other eukaryotes. Two other subfamilies, yqeV and CDKAL1, are named after a Bacillus subtilis and a human protein, respectively. While yqeV-like proteins are found in bacteria, CDKAL1 subfamily members occur in eukaryotes and in archaebacteria. The likely MTTases from these 4 subfamilies contain an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain (see ). The core forms a radical SAM fold (or AdoMet radical), containing a cysteine motif CxxxCxxC that binds a [4Fe-4S]cluster [, , ]. A reducing equivalent from the [4Fe-4S]+ cluster is used to cleave S-adenosylmethionine (SAM) to generate methionine and a 5'-deoxyadenosyl radical. The latter is thought to produce a reactive substrate radical that is amenable to sulphur insertion [, ]. The N-terminal MTTase domain contains 3 cysteines that bind a second [4Fe-4S]cluster, in addition to the radical-generating [4Fe-4S]cluster, which could be involved in the thiolation reaction. The C-terminal TRAM domain is not shared with other radical SAM proteins outside the MTTase family. The TRAM domain can bind to RNA substrate and seems to be important for substrate recognition. The tertiary structure of the central radical SAM fold has six beta/alpha motifs resembling a three-quarter TIM barrel core (see ) []. The N-terminal MTTase domain might form an additional [beta/alpha]2 TIM barrel unit [].
