title: Crystallographic evidence for substrate-assisted GTP hydrolysis by a small GTP binding protein.
abstract: GTP hydrolysis by small GTP binding proteins of the Ras superfamily is a universal reaction that controls multiple cellular regulations. Its enzymic mechanism has been the subject of long-standing debates as to the existence/identity of the general base and the electronic nature of its transition state. Here we report the high-resolution crystal structure of a small GTP binding protein, Rab11, solved in complex with GDP and Pi. Unexpectedly, a Pi oxygen and the GDP-cleaved oxygen are located less than 2.5 A apart, suggesting that they share a proton, likely in the form of a low-barrier hydrogen bond. This implies that the gamma-phosphate of GTP was protonated; hence, that GTP acts as a general base. Furthermore, this interaction should establish at, and stabilize, the transition state. Altogether, we propose a revised model for the GTPase reaction that should reconcile earlier models into a unique substrate-assisted mechanism.
authors.affiliation: Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Pasqualato
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Cherfils
mesh_terms: D003461:Crystallography; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D006860:Hydrogen Bonding; D006868:Hydrolysis
chemical_list: D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins