title: Structural evidence for a common intermediate in small G protein-GEF reactions.
abstract: Rho of plants (Rop) proteins belong to the superfamily of small GTP-binding (G) proteins and are vital regulators of signal transduction in plants. In order to become activated, Rop proteins need to exchange GDP for GTP, an intrinsically slow process catalyzed by guanine nucleotide exchange factors (GEFs). RopGEFs show no homology to animal RhoGEFs, and the catalytic mechanism remains elusive. GEF-catalysed nucleotide exchange proceeds via transient ternary and stable binary complexes. While a number of structural studies have analyzed binary nucleotide-free G protein-GEF complexes, very little is known about the ternary complexes. Here we report the X-ray structure of the catalytic PRONE domain of RopGEF8 from Arabidopsis thaliana, both alone and in a ternary complex with Rop4 and GDP. The features of the latter complex, a transient intermediate of the exchange reaction never directly observed before, suggest a common mechanism of catalyzed nucleotide exchange applicable to small G proteins in general.
authors.affiliation: Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Thomas
authors.forename: Inka
authors.initials: I
authors.lastname: Fricke
authors.forename: Andrea
authors.initials: A
authors.lastname: Scrima
authors.forename: Antje
authors.initials: A
authors.lastname: Berken
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D002384:Catalysis; D018360:Crystallography, X-Ray; D019204:GTP-Binding Proteins / Q000737:chemistry; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000737:chemistry; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D064067:Rho Guanine Nucleotide Exchange Factors
chemical_list: D029681:Arabidopsis Proteins; D020662:Guanine Nucleotide Exchange Factors; D050505:Mutant Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; C516916:RopGEF8 protein, Arabidopsis; D006153:Guanosine Diphosphate; D019204:GTP-Binding Proteins; C511948:Rop4 protein, Arabidopsis; D020559:Monomeric GTP-Binding Proteins