title: A new function of p120-GTPase-activating protein. Prevention of the guanine nucleotide exchange factor-stimulated nucleotide exchange on the active form of Ha-ras p21.
abstract: This work studies the coordination of the action of GTPase-activating protein (GAP) and guanine nucleotide exchange factor (GEF) on activated human c-Ha-Ras p21. Purified human p120-GAP was obtained with a new efficient procedure. To distinguish the GTPase-activating effect of p120-GAP from other effects dependent on the interaction with activated Ha-Ras, the nonhydrolyzable GTP analogue guanosine 5'-O-(thiotriphosphate) (GTPgammaS) was used. The results showed that the GTPgammaS/GTPgammaS exchange enhanced by the C-terminal catalytic domain of the yeast GEF Sdc25p (C-Sdc25p) is prevented by p120-GAP. This effect is strictly specific for the activated form of Ha-Ras, the target of GAP; no effect on Ha-Ras.GDP was detectable. The GAP catalytic domain also inhibited C-Sdc25p but to a lower extent. The interfering effect by p120-GAP was also evident in a homologous mammalian system, using full-length mouse RasGEF, its C-terminal half-molecule, or C-terminal catalytic domain. As a consequence of this inhibition, presence of p120-GAP enhanced the regeneration of Ha-Ras.GTPgammaS by GEF at a GDP:GTPgammaS ratio mimicking the in vivo GDP:GTP ratio. Our work describes a novel function of p120-GAP and suggests a mechanism by which GAP protects Ha-Ras.GTP in vivo against unproductive exchanges. This constrain is likely involved in the regulation of the physiological GDP/GTP cycle of Ras and in the action of p120-GAP as downstream effector of Ras. Helix alpha3 is proposed as a Ras element playing a key-role in the interference between GAP and GEF on Ras.
authors.affiliation: Groupe de Biophysique-Equipe 2, Ecole Polytechnique, F-91128 Palaiseau Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Giglione
authors.forename: M C
authors.initials: MC
authors.lastname: Parrini
authors.forename: S
authors.initials: S
authors.lastname: Baouz
authors.forename: A
authors.initials: A
authors.lastname: Bernardi
authors.forename: A
authors.initials: A
authors.lastname: Parmeggiani
mesh_terms: D000818:Animals; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D051379:Mice; D008961:Models, Structural; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011506:Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D020703:ras GTPase-Activating Proteins; D020666:ras-GRF1
chemical_list: D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; D011506:Proteins; D011994:Recombinant Proteins; D020703:ras GTPase-Activating Proteins; D020666:ras-GRF1; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010749:Phosphoprotein Phosphatases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)