title: RasGEF1A and RasGEF1B are guanine nucleotide exchange factors that discriminate between Rap GTP-binding proteins and mediate Rap2-specific nucleotide exchange.
abstract: The highly conserved RasGEF1 family of proteins contain a C-terminal CDC25-Ras exchange motif domain and an N-terminal RasGEF-N domain, and are of unknown function and specificity. Using purified RasGEF1A and RasGEF1B proteins, as well as Ras family proteins, we established that RasGEF1A and RasGEF1B function as very specific exchange factors for Rap2, a member of the Rap subfamily of Ras-like G-proteins. They do not act on Rap1 or other members of the Ras subfamily. Although Rap2 was implicated in the regulation of cell adhesion, the establishment of cell morphology, and the modulation of synapses in neurons, no specific guanine nucleotide exchange factor for Rap2 was previously identified. Using reciprocal site-directed mutagenesis, we analyzed residues that allow RasGEF1 proteins to discriminate between Rap1 and Rap2, and we were able to identify Phe39 in the switch I region of Rap2 as a specificity residue. Mutation of the corresponding Ser39 in Rap1 changed the specificity and allowed the nucleotide exchange of Rap1(S39F) to be stimulated by RasGEF1B.
authors: Department of Molecular Biology and Genetics, Bilkent University, Ankara, Turkey.
authors: Elif
authors: E
authors: Yaman
authors: Raphael
authors: R
authors: Gasper
authors: Carolin
authors: C
authors: Koerner
authors: Alfred
authors: A
authors: Wittinghofer
authors: Uygar H
authors: UH
authors: Tazebay
mesh_terms: D006801:Humans; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine; D012694:Serine; D013379:Substrate Specificity; D020668:rap GTP-Binding Proteins / Q000378:metabolism*; D020663:ras Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D010649:Phenylalanine; D012694:Serine; D020668:rap GTP-Binding Proteins; D020663:ras Guanine Nucleotide Exchange Factors; C516782:RASGEF1A protein, human; C543919:RASGEF1B protein, human; C116756:RAP2A protein, human