Small GTPase superfamily, Tem1
InterPro Protein Domain record
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description
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<p>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 [<cite idref="PUB00052600"/>, <cite idref="PUB00004087"/>]. 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 [<cite idref="PUB00000348"/>].</p><p>Crystallographic analysis of various small G proteins revealed the presence of a 20 kDa catalytic domain that is unique for the whole superfamily [<cite idref="PUB00004087"/>, <cite idref="PUB00023196"/>]. The domain is built of five alpha helices (A1-A5), six beta-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 Mg(2+) 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 Mg(2+) 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 [<cite idref="PUB00015117"/>].</p><p>The small GTPase superfamily can be divided into at least 8 different families, including:</p><ul> <li>Arf small GTPases. GTP-binding proteins involved in protein trafficking by modulating vesicle budding and uncoating within the Golgi apparatus.</li> <li>Ran small GTPases. GTP-binding proteins involved in nucleocytoplasmic transport. Required for the import of proteins into the nucleus and also for RNA export.</li> <li>Rab small GTPases. GTP-binding proteins involved in vesicular traffic.</li> <li>Rho small GTPases. GTP-binding proteins that control cytoskeleton reorganisation.</li> <li>Ras small GTPases. GTP-binding proteins involved in signalling pathways.</li> <li>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).</li> <li>Mitochondrial Rho (Miro). Small GTPase domain found in mitochondrial proteins involved in mitochondrial trafficking.</li> <li>Roc small GTPases domain. Small GTPase domain always found associated with the COR domain.</li> </ul><p>GTP-binding protein TEM1 is involved in termination of M phase of the cell cycle. It may play a role in triggering the degradation of G2 cyclin to inactivate M-phase promoting factor at the termination of mitosis. TEM1 acts upstream of CDC15 kinase and may be required to activate the CDC15 protein kinase pathway. The protein interacts with CDC15 and AMN1. AMN1 and CDC15 compete for association with TEM1 [<cite idref="PUB00053139"/>]. </p>
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Small GTPase superfamily, Tem1
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signatures_SMART
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InterPro Protein Domain record
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