Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.25 (triphosphatase)
 1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Unlike the alpha subunits of heterotrimeric guanosine triphosphate (GTP)-binding proteins, Ras-related GTP-binding proteins have hitherto been considered not to bind or become activated by tetrafluoroaluminate (AIF4-). However, the product of the proto-oncogene ras in its guanosine diphosphate (GDP)-bound form interacted with AIF4 - in the presence of stoichiometric amounts of either of the guanosine triphosphatase (GTPase)-activating proteins (GAPs) p120GAP and neurofibromin. Neither oncogenic Ras nor a GAP mutant without catalytic activity produced such a complex. Together with the finding that the Ras-binding domain of the protein kinase c-Raf, whose binding site on Ras overlaps that of the GAPs, did not induce formation of such a complex, this result suggests that GAP and neurofibromin stabilize the transition state of the GTPase reaction of Ras.
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PMID:Formation of a transition-state analog of the Ras GTPase reaction by Ras-GDP, tetrafluoroaluminate, and GTPase-activating proteins. 865 79

The three-dimensional structure of the complex between human H-Ras bound to guanosine diphosphate and the guanosine triphosphatase (GTPase)-activating domain of the human GTPase-activating protein p120GAP (GAP-334) in the presence of aluminum fluoride was solved at a resolution of 2.5 angstroms. The structure shows the partly hydrophilic and partly hydrophobic nature of the communication between the two molecules, which explains the sensitivity of the interaction toward both salts and lipids. An arginine side chain (arginine-789) of GAP-334 is supplied into the active site of Ras to neutralize developing charges in the transition state. The switch II region of Ras is stabilized by GAP-334, thus allowing glutamine-61 of Ras, mutation of which activates the oncogenic potential, to participate in catalysis. The structural arrangement in the active site is consistent with a mostly associative mechanism of phosphoryl transfer and provides an explanation for the activation of Ras by glycine-12 and glutamine-61 mutations. Glycine-12 in the transition state mimic is within van der Waals distance of both arginine-789 of GAP-334 and glutamine-61 of Ras, and even its mutation to alanine would disturb the arrangements of residues in the transition state.
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PMID:The Ras-RasGAP complex: structural basis for GTPase activation and its loss in oncogenic Ras mutants. 951 63

Arachidonic acid, phosphatidic acid, and other lipids inhibit the catalytic fragment of neurofibromin more potently than that of p120 guanosine triphosphatase-activating protein (GAP). The effects of fatty acids other than arachidonic acid on full-length neurofibromin and p120 GAP, to our knowledge, have not been studied. In this study, we analyzed the effects of eight nutritionally relevant fatty acids on guanosine triphosphatase (GTPase) stimulatory activity of full-length neurofibromin and p120 GAP. The fatty acids tested were saturated stearic acid, monounsaturated oleic acid, and three n-6 and three n-3 polyunsaturated fatty acids. Analysis was performed by Ras immunoprecipitation GTPase assay. The full-length p120 GAP expressed in insect Sf9 cells and immunoaffinity-purified full-length neurofibromin were used. In contrast to neurofibromin, which was readily inhibited by stearic and oleic acid, p120 GAP was only weakly inhibited even at high concentrations (> 80 microM). Neurofibromin was also two- to threefold more sensitive to inhibition by other fatty acids tested. A chimeric protein in which the neurofibromin catalytic domain was fused to the NH2-terminal sequences of p120 GAP was used to determine that differential sensitivity to fatty acid inhibition maps to the catalytic domain of the proteins. These results indicate that nutritionally relevant fatty acids can modulate the GTPase function of c-Ha-Ras protein by inhibiting GTPase stimulatory activity of two Ras regulators, full-length neurofibromin and p120 GAP, at physiologically relevant concentrations in vitro.
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PMID:Differential regulation of neurofibromin and p120 GTPase-activating protein by nutritionally relevant fatty acids. 958 27

Recent cloning of a rat brain phosphatidylinositol 3,4, 5-trisphosphate binding protein, centaurin alpha, identified a novel gene family based on homology to an amino-terminal zinc-binding domain. In Saccharomyces cerevisiae, the protein with the highest homology to centaurin alpha is Gcs1p, the product of the GCS1 gene. GCS1 was originally identified as a gene conditionally required for the reentry of cells into the cell cycle after stationary phase growth. Gcs1p was previously characterized as a guanosine triphosphatase-activating protein for the small guanosine triphosphatase Arf1, and gcs1 mutants displayed vesicle-trafficking defects. Here, we have shown that similar to centaurin alpha, recombinant Gcs1p bound phosphoinositide-based affinity resins with high affinity and specificity. A novel GCS1 disruption strain (gcs1Delta) exhibited morphological defects, as well as mislocalization of cortical actin patches. gcs1Delta was hypersensitive to the actin monomer-sequestering drug, latrunculin-B. Synthetic lethality was observed between null alleles of GCS1 and SLA2, the gene encoding a protein involved in stabilization of the actin cytoskeleton. In addition, synthetic growth defects were observed between null alleles of GCS1 and SAC6, the gene encoding the yeast fimbrin homologue. Recombinant Gcs1p bound to actin filaments, stimulated actin polymerization, and inhibited actin depolymerization in vitro. These data provide in vivo and in vitro evidence that Gcs1p interacts directly with the actin cytoskeleton in S. cerevisiae.
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PMID:GCS1, an Arf guanosine triphosphatase-activating protein in Saccharomyces cerevisiae, is required for normal actin cytoskeletal organization in vivo and stimulates actin polymerization in vitro. 1006 5