title: Biochemical studies of the mechanism of action of the Cdc42-GTPase-activating protein.
abstract: The small GTP-binding proteins Rac, Rho, and Cdc42 were shown to mediate a variety of signaling pathways including cytoskeletal rearrangements, cell-cycle progression, and transformation. Key to the proper function of these GTP-binding proteins is an efficient shut-off mechanism that ensures the decay of the signal. Regulatory proteins termed GAPs (GTPase-activating proteins) enhance the intrinsic GTP hydrolysis of the GTP-binding proteins, thereby ensuring signal termination. We have used site-specific mutagenesis to elucidate the limit domain for GAP activity in Cdc42-GAP, and show that in addition to the known GAP-homology domain (three conserved boxes), a C-terminal region outside that domain is also essential for GAP activity. In addition, we have replaced the conserved arginine (Arg305), which was suggested by structural studies to be a key catalytic residue, with an alanine and found that the R305A Cdc42-GAP mutant has a greatly diminished catalytic capacity but is still able to bind Cdc42 with high affinity. Thus, a key catalytic role for this residue is confirmed. However, we also present evidence for the involvement of an additional residue(s), since the R305A Cdc42-GAP mutant still exhibits measurable activity. Some of this residual activity might result from a neighboring arginine, since a double mutant R305A/R306A shows a further decrease in catalytic activity.
authors.affiliation: Department of Pharmacology, Veterinary Medical Center, Cornell University, Ithaca, New York 14853, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Leonard
authors.forename: R
authors.initials: R
authors.lastname: Lin
authors.forename: R A
authors.initials: RA
authors.lastname: Cerione
authors.forename: D
authors.initials: D
authors.lastname: Manor
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D018797:Cell Cycle Proteins / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020764:cdc42 GTP-Binding Protein; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; D011506:Proteins; D020703:ras GTPase-Activating Proteins; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D018631:ras Proteins