title: Crystal structure of a small G protein in complex with the GTPase-activating protein rhoGAP.
abstract: Small G proteins transduce signals from plasma-membrane receptors to control a wide range of cellular functions. These proteins are clustered into distinct families but all act as molecular switches, active in their GTP-bound form but inactive when GDP-bound. The Rho family of G proteins, which includes Cdc42Hs, activate effectors involved in the regulation of cytoskeleton formation, cell proliferation and the JNK signalling pathway. G proteins generally have a low intrinsic GTPase hydrolytic activity but there are family-specific groups of GTPase-activating proteins (GAPs) that enhance the rate of GTP hydrolysis by up to 10(5) times. We report here the crystal structure of Cdc42Hs, with the non-hydrolysable GTP analogue GMPPNP, in complex with the GAP domain of p50rhoGAP at 2.7A resolution. In the complex Cdc42Hs interacts, mainly through its switch I and II regions, with a shallow pocket on rhoGAP which is lined with conserved residues. Arg 85 of rhoGAP interacts with the P-loop of Cdc42Hs, but from biochemical data and by analogy with the G-protein subunit G(i alpha1), we propose that it adopts a different conformation during the catalytic cycle which enables it to stabilize the transition state of the GTP-hydrolysis reaction.
authors.affiliation: National Institute for Medical Research, London, UK.
authors.forename: K
authors.initials: K
authors.lastname: Rittinger
authors.forename: P A
authors.initials: PA
authors.lastname: Walker
authors.forename: J F
authors.initials: JF
authors.lastname: Eccleston
authors.forename: K
authors.initials: K
authors.lastname: Nurmahomed
authors.forename: D
authors.initials: D
authors.lastname: Owen
authors.forename: E
authors.initials: E
authors.lastname: Laue
authors.forename: S J
authors.initials: SJ
authors.lastname: Gamblin
authors.forename: S J
authors.initials: SJ
authors.lastname: Smerdon
mesh_terms: D001120:Arginine / Q000737:chemistry; D018797:Cell Cycle Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry*; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D020764:cdc42 GTP-Binding Protein
chemical_list: D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; C085379:rho GTPase-activating protein; D006160:Guanosine Triphosphate; D001120:Arginine; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein