Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

A variety of systems use nucleoside triphosphate hydrolysis to control or provide energy for biological processes, mediated through protein-protein interactions. The nature of this coupling may vary, but often there is a degree of similarity. In this paper, two systems are compared: actomyosin in muscle and p21ras in a signal transduction pathway as yet undefined. The mechanism of the nucleotide triphosphate hydrolysis and the consequent changes in the protein-nucleotide complex have been investigated, to understand how the coupling to biological function is achieved. The basal nucleoside triphosphatase mechanisms are compared and the roles of proteins that activate the hydrolysis, actin and GAP, are discussed. The cleavage process was probed by stereochemical techniques to determine the basic mechanism, of either a phosphorylated enzyme intermediate or direct displacement of nucleoside diphosphate by water. Phosphate-water oxygen exchange probes were used to investigate nucleoside triphosphate and inorganic phosphate release steps. A new method of probing the kinetics of inorganic phosphate release directly has been developed. In muscle, this process seems likely to be related directly to force generation. In the GAP-ras system, measurement of phosphate release is allowing the mechanism of the GAP-p21ras interaction to be probed.
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PMID:The role of nucleoside triphosphate hydrolysis in transducing systems: p21ras and muscle. 135 Dec 91

The interaction between the low molecular weight G protein ras p21 and a guanosine triphosphatase activating protein (GAP) uncouples a heterotrimeric G protein (Gk) from muscarinic receptors. Through the use of isolated atrial cell membranes and genetically engineered GAP deletion mutants, the src homology regions (SH2-SH3) at the amino terminus of GAP have been identified as the domains responsible for this effect. Deletion of the domain required to stimulate the guanosine triphosphatase activity of ras p21 relieves the requirement for ras p21 in this system. A model is presented that suggests that ras p21 induces a conformational change in GAP, which allows the SH2-SH3 regions of GAP to function.
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PMID:GAP domains responsible for ras p21-dependent inhibition of muscarinic atrial K+ channel currents. 155 41

The gene for von Recklinghausen neurofibromatosis (NF1) was recently identified by positional cloning and found to code for a large, ubiquitously expressed protein. This protein has both structural and functional similarity to a family of proteins with guanosine triphosphatase-activating properties, involved in the regulation of the protooncogene ras. One of the postulated functions of the NF1 gene product may relate to its ability to regulate ras-mediated cell proliferation. Selective pharmacotherapy directed at downregulating ras may be of benefit to patients with NF1.
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PMID:Recent progress toward understanding the molecular biology of von Recklinghausen neurofibromatosis. 159 91

The ras proto-oncogene products appear to relay intracellular signals via the Ras guanosine triphosphatase (GTPase) activator protein, GAP. In dog epithelial cells expressing human platelet-derived growth factor (PDGF) receptors, binding of PDGF caused approximately one-tenth of the total GAP molecules to complex with the receptor. Studies with mutant PDGF receptors showed that maximum association required both receptor kinase activity and phosphorylatable tyrosine residues at both the identified sites of receptor autophosphorylation.
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PMID:Binding of GAP to activated PDGF receptors. 215 84

Krev-1 is known to suppress transformation by ras. However, the mechanism of the suppression is unclear. The protein product of Krev-1, Rap1A-p21, is identical to Ras-p21 proteins in the region where interaction with guanosine triphosphatase (GTPase) activating protein (GAP) is believed to occur. Therefore, the ability of GAP to interact with Rap1A-p21 was tested. Rap1A-p21 was not activated by GAP but bound tightly to GAP and was an effective competitive inhibitor of GAP-mediated Ras-GTPase activity. Binding of GAP to Rap1A-p21 was strictly guanosine triphosphate (GTP)-dependent. The ability of Rap1A-p21 to bind tightly to GAP may account for Krev-1 suppression of transformation by ras. This may occur by preventing interaction of GAP with Ras-p21 or with other cellular proteins necessary for GAP-mediated Ras GTPase activity.
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PMID:Inhibition of GTPase activating protein stimulation of Ras-p21 GTPase by the Krev-1 gene product. 216 10

The crystal structure at 2.7 A resolution of the normal human c-H-ras oncogene protein lacking a flexible carboxyl-terminal 18 residue reveals that the protein consists of a six-stranded beta sheet, four alpha helices, and nine connecting loops. Four loops are involved in interactions with bound guanosine diphosphate: one with the phosphates, another with the ribose, and two with the guanine base. Most of the transforming proteins (in vivo and in vitro) have single amino acid substitutions at one of a few key positions in three of these four loops plus one additional loop. The biological functions of the remaining five loops and other exposed regions are at present unknown. However, one loop corresponds to the binding site for a neutralizing monoclonal antibody and another to a putative "effector region"; mutations in the latter region do not alter guanine nucleotide binding or guanosine triphosphatase activity but they do reduce the transforming activity of activated proteins. The data provide a structural basis for understanding the known biochemical properties of normal as well as activated ras oncogene proteins and indicate additional regions in the molecule that may possibly participate in other cellular functions.
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PMID:Three-dimensional structure of an oncogene protein: catalytic domain of human c-H-ras p21. 244 79

A 47-kilodalton neutrophil cytosol factor (NCF-47k), required for activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase superoxide (O2-.) production, is absent in most patients with autosomal recessive chronic granulomatous disease (AR-CGD). NCF-47k cDNAs were cloned from an expression library. The largest clone predicted a 41.9-kD protein that contained an arginine and serine-rich COOH-terminal domain with potential protein kinase C phosphorylation sites. A 33-amino acid segment of NCF-47k shared 49% identity with ras p21 guanosine triphosphatase activating protein. Recombinant NCF-47k restored O2-. -producing activity to AR-CGD neutrophil cytosol in a cell-free assay. Production of active recombinant NCF-47k will enable functional regions of this molecule to be mapped.
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PMID:Recombinant 47-kilodalton cytosol factor restores NADPH oxidase in chronic granulomatous disease. 254 47

The role of guanine nucleotides in ras p21 function was determined by using the ability of p21 protein to induce maturation of Xenopus oocytes as a quantitative assay for biological activity. Two oncogenic mutant human N-ras p21 proteins, Asp12 and Val12, actively induced maturation, whereas normal Gly12 p21 was relatively inactive in this assay. Both mutant proteins were found to be associated with guanosine triphosphate (GTP) in vivo. In contrast, Gly12 p21 was predominantly guanosine diphosphate (GDP)-bound because of a dramatic stimulation of Gly12 p21-associated guanosine triphosphatase (GTPase) activity. A cytoplasmic protein was shown to be responsible for this increase in activity. This protein stimulated GTP hydrolysis by purified Gly12 p21 more than 200-fold in vitro, but had no effect on Asp12 or Val12 mutants. A similar factor could be detected in extracts from mammalian cells. It thus appears that, in Xenopus oocytes, this protein maintains normal p21 in a biologically inactive, GDP-bound state through its effect on GTPase activity. Furthermore, it appears that the major effect of position 12 mutations is to prevent this protein from stimulating p21 GTPase activity, thereby allowing these mutants to remain in the active GTP-bound state.
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PMID:A cytoplasmic protein stimulates normal N-ras p21 GTPase, but does not affect oncogenic mutants. 282 24

A cytoplasmic protein that greatly enhances the guanosine triphosphatase (GTPase) activity of N-ras protein but does not affect the activity of oncogenic ras mutants has been recently described. This protein (GAP) is shown here to be ubiquitous in higher eukaryotes and to interact with H-ras as well as with N-ras proteins. To identify the region of ras p21 with which GAP interacts, 21 H-ras mutant proteins were purified and tested for their ability to undergo stimulation of GTPase activity by GAP. Mutations in nonessential regions of H-ras p21 as well as mutations in its carboxyl-terminal domain (residues 165-185) and purine binding region (residues 117 and 119) did not decrease the ability of the protein to respond to GAP. In addition, an antibody against the carboxyl-terminal domain did not block GAP activity, supporting the conclusion that GAP does not interact with this region. Transforming mutations at positions 12, 59, and 61 (the phosphoryl binding region) abolished GTPase stimulation by GAP. Point mutations in the putative effector region of ras p21 (amino acids 35, 36, and 38) were also insensitive to GAP. However, a point mutation at position 39, shown previously not to impair effector function, did not alter GAP-p21 interaction. These results indicate that GAP interaction may be essential for ras p21 biological activity and that it may be a ras effector protein.
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PMID:Guanosine triphosphatase activating protein (GAP) interacts with the p21 ras effector binding domain. 283 17

Cytogeneticists recognize that karyotypic abnormalities are associated with specific malignancies. In 1960, Nowell described the Philadelphia chromosome (Ph) and its relationship to chronic myelogenous leukemia (CML). Subsequent work in molecular genetics and biology has revealed that the Ph is a translocation that causes fusion of gene sites that code for the break cluster region (BCR) and the avian blastic leukemia (ABL) proteins. This so-called fusion protein is present in a large percentage of the patients who have CML. A related fusion protein is seen in about one third of patients with acute lymphoblastic leukemia. The BCR-ABL fusion protein results in increased tyrosine kinase activity. The mechanism of action is thought to be via signal transduction related to guanosine triphosphatase activating protein which interacts with a ras-p21 binding protein. Acute promyelocytic leukemia (APL) is associated with the cytogenetic abnormality of t(15;17). This alters the promyelocytic leukemia (PML) and the retinoic acid receptor alpha (RARA) gene sites. Two fusion proteins are the result of this cytogenetic abnormality. They are termed PML-RARA and RARA-PML. Only one, the PML-RARA, is associated with APL. The PML-RARA chimeric protein has two zinc finger-like regions. It retains the ligand binding domain of RARA. The protein called PML has some similarities with a family of proteins which are thought to fuse to proto-oncogenes and to act as transforming proteins. The role of classical cytogenetics and the added capability of molecular biology has helped to elucidate some of the potential mechanisms for the development of cancer and provided additional understanding of neoplasia. (ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cytogenetics, gene fusions, and cancer. 748 13


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