| Primary Identifier | IPR020859 | Type | Domain |
| Short Name | ROC_dom |
| description | Small GTPases form an independent superfamily within the larger class ofregulatory GTP hydrolases. This superfamily contains proteins that control avast number of important processes and possess a common, structurallypreserved GTP-binding domain [, ]. Sequence comparisons of small G proteinsfrom various species have revealed that they are conserved in primarystructures 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), sixβ-strands (B1-B6) and five polypeptide loops (G1-G5). A structuralcomparison of the GTP- and GDP-bound form, allows one to distinguish twofunctional loop regions: switch I and switch II that surround thegamma-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 ofthe phosphate groups. The G3 loop provides residues for Mg(2+) and phosphatebinding and is located at the N terminus of the A2 helix. The G1 and G3 loopsare sequentially similar to Walker A and Walker B boxes that are found inother nucleotide binding motifs. The G2 loop connects the A1 helix and the B2strand and contains a conserved Thr residue responsible for Mg(2+) binding.The guanine base is recognised by the G4 and G5 loops. The consensus sequenceNKXD of the G4 loop contains Lys and Asp residues directly interacting withthe nucleotide. Part of the G5 loop located between B6 and A5 acts as arecognition site for the guanine base [].The small GTPase superfamily can be divided in 8 different families:Arf small GTPases. GTP-binding proteins involved in protein trafficking bymodulating vesicle budding and un-coating within the Golgi apparatusRan small GTPases. GTP-binding proteins involved in nucleocytoplasmictransport. Required for the import of proteins into the nucleus and alsofor RNA exportRab small GTPases. GTP-binding proteins involved in vesicular traffic.Rho small GTPases. GTP-binding proteins that control cytoskeletonreorganisationRas small GTPases. GTP-binding proteins involved in signaling pathwaysSar1 small GTPases. Small GTPase component of the coat protein complex II(COPII) which promotes the formation of transport vesicles from theendoplasmic reticulum (ER)Mitochondrial Rho (Miro). Small GTPase domain found in mitochondrialproteins involved in mitochondrial traffickingRoc small GTPases domain. Small GTPase domain always found associated withthe COR domain.This entry represents the Roc small GTPase domain. |
