|PROSITE documentation PDOC51417 [for PROSITE entry PS51421]|
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 [1,2]. 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 20 kDa catalytic domain that is unique for the whole superfamily (see <PDB:5P21>) [2,4]. The domain is built of five α 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 γ-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 recognized 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 devided in 8 different families:
The various small GTPase family profiles cover the whole catalyticaly conserved region.Last update:
March 2015 / Profile revised.
PROSITE methods (with tools and information) covered by this documentation:
|1||Authors||Bourne H.R., Sanders D.A., McCormick F.|
|Title||The GTPase superfamily: a conserved switch for diverse cell functions.|
|2||Authors||Bourne H.R., Sanders D.A., McCormick F.|
|Title||The GTPase superfamily: conserved structure and molecular mechanism.|
|3||Authors||Valencia A., Chardin P., Wittinghofer A., Sander C.|
|Title||The ras protein family: evolutionary tree and role of conserved amino acids.|
|4||Authors||Pai E.F., Krengel U., Petsko G.A., Goody R.S., Kabsch W., Wittinghofer A.|
|Title||Refined crystal structure of the triphosphate conformation of H-ras p21 at 1.35 A resolution: implications for the mechanism of GTP hydrolysis.|
|Source||EMBO J. 9:2351-2359(1990).|
|5||Authors||Paduch M., Jelen F., Otlewski J.|
|Title||Structure of small G proteins and their regulators.|
|Source||Acta Biochim. Pol. 48:829-850(2001).|