Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The kinetic method and selective chemical modification have been used in studies of the kinetic manifestations of active site interactions in D-glyceraldehyde-3-phosphate dehydrogenase (GAP dehydrogenase). The reactions of glyceraldehyde and glyceraldehyde-3-phosphate oxidation were studied in the absence of substrate excess. In support of the data obtained previously it was shown that only a part of the tightly bound NAD molecules can be reduced after substrate addition. "Partial reducibility" is observed at various degrees of saturation of the enzyme with NAD involving a single NAD molecule per tetrametric enzyme. These facts can hardly be explained by assumption of functional non-equivalence of active sites, whether induced by coenzyme or preexisting in the apoenzyme. It was proven by selective alkylation of the catalytic SH groups that "partial reducibility" is due to the circumstance that equilibrium in the system under investigation is established at nearly equal NAD and NADH concentrations. A plot of initial reaction rates versus NAD concentration (at non-saturating substrate concentrations) gives S-shaped curves; this is explained by considerable enzyme activation upon saturation of the fourth site with coenzyme. After modification of three active sites with iodoacetate the S-shape of the curve disappeared. This fact leads to the conclusion that active site interactions are required for formation of the S-shaped curves. The activity of a single site functioning in the modified enzyme reached values equal to those of the active sites in the native enzyme in the fully activated state. A model is proposed which can explaine the variations in mode of enzyme activation in the native and modified states. It is suggested that the surroundings of all four SH groups must be altered in order to activate the enzyme; such changes can be induced either by alkylation of the SH groups or by NAD binding. Evidence is presented that important functional properties of GAP dehydrogenase cannot be elucidated at low enzyme concentrations and with excess of substrates: three active sites are saturated under such conditons and practically inactive, and the fourth site obeys Michaelis - Menten kinetics.
Mol Biol (Mosk)
PMID:[Kinetic manifestations of the interaction of active centers in swine skeletal muscle D-glyceraldehyde-3-phosphate dehydrogenase]. 18 4

Several characteristics of the nucleic factor of tumors which is thought to play an important role in suppression of tumor immunity was investigated. This nucleic factor differs from native double-stranded DNA of eukaryotic nuclei by base composition (A: T: G : C = 1: 1.44 : 0.91: 0.69); its affinity to GAP and hyperchromic effect were lower than those in native DNA. Heating above 80 degrees in 1 N KOH destroyed the nucleic factor to fragments that could not be detected in 8% PAK electrophoresis. The results of this and previous reports lead us to a hypothesis that the nucleic factor is a DNA molecule consisting of single- and double-stranded regions, as well as short insertions of RNA. The double-stranded regions in this molecule possess non-parrallel breaks.
Mol Biol (Mosk)
PMID:[Structural peculiarities of the nucleic factor from ascitic fluid of tumors]. 74 2

Two distinct GAPs of 120 and 235 kDa called GAP1 and NF1 serve as attenuators of Ras, a member of GTP-dependent signal transducers, by stimulating its intrinsic guanosine triphosphatase (GTPase) activity. The GAP1 (also called Ras GAP) is highly specific for Ras and does not stimulate the intrinsic GTPase activity of Rap1 or Rho. Using GAP1C, the C-terminal GTPase activating domain (residues 720-1044) of bovine GAP1, we have shown previously that the GAP1 specificity is determined by the Ras domain (residues 61-65) where Gln61 plays the primary role. The corresponding domain (residues 1175-1531) of human NF1 (called NF1C), which shares only 26% sequence identity with the GAP1C, also activates Ras GTPases. In this article, we demonstrate that the NF1C, like the GAP1C, is highly specific for Ras and does not activate either Rap1 or Rho GTPases. Furthermore, using a series of chimeric Ras/Rap1 and mutated Ras GTPases, we show that Gln at position 61 of the GTPases primarily determines that NF1C as well as GAP1C activates Ras GTPases, but not Rap1 GTPases, and Glu at position 63 of the GTPases is required for maximizing the sensitivity of Ras GTPases to both NF1C and GAP1C. Interestingly, replacement of Glu63 of c-HaRas by Lys reduces its intrinsic GTPase activity and abolishes the GTPase activation by both NF1C and GAP1C. Thus, the potentiation of oncogenicity by Lys63 mutation of c-HaRas appears primarily to be due to the loss of its sensitivity to the two major Ras signal attenuators (NF1 and GAP1).
Mol Biol Cell 1992 Dec
PMID:The role of Gln61 and Glu63 of Ras GTPases in their activation by NF1 and Ras GAP. 136 1

rap1GAP is a GTPase-activating protein that specifically stimulates the GTP hydrolytic rate of p21rap1. We have defined the catalytic domain of rap1GAP by constructing a series of cDNAs coding for mutant proteins progressively deleted at the amino- and carboxy-terminal ends. Analysis of the purified mutant proteins shows that of 663 amino acid residues, only amino acids 75 to 416 are necessary for full GAP activity. Further truncation at the amino terminus resulted in complete loss of catalytic activity, whereas removal of additional carboxy-terminal residues dramatically accelerated the degradation of the protein in vivo. The catalytic domain we have defined excludes the region of rap1GAP which undergoes phosphorylation on serine residues. We have further defined this phosphoacceptor region of rap1GAP by introducing point mutations at specific serine residues and comparing the phosphopeptide maps of the mutant proteins. Two of the sites of phosphorylation by cyclic AMP (cAMP)-dependent kinase were localized to serine residues 490 and 499, and one site of phosphorylation by p34cdc2 was localized to serine 484. In vivo, rap1GAP undergoes phosphorylation at four distinct sites, two of which appear to be identical to the sites phosphorylated by cAMP-dependent kinase in vitro.
Mol Cell Biol 1992 Oct
PMID:Localization of the rap1GAP catalytic domain and sites of phosphorylation by mutational analysis. 140 53

The rotund (rn) locus of Drosophila melanogaster at cytogenetic position 84D3,4 has been isolated and cloned on the basis of the mutant phenotype: an absence of structures in the subdistal regions of the appendages. The shortened appendages are the consequence of a localized cell death in the imaginal discs, precursors of the adult appendages. Physical characterization of the rn locus has demonstrated that it is relatively large, occupying a minimum of 50 kb. There are two major transcripts of 1.7 kb (m1.7) and 5.3 kb (m5.3). We present here the sequence analysis of m1.7 and its putative product, rnprot1.7, and show that rnprot1.7 is similar to the product of the human n-chimaerin gene, which is expressed in brain and testes. Recently, the GAP activity of n-chimaerin was demonstrated and shown to be specific for the Rac subfamily of the Ras oncoproteins. The Rac proteins have been implicated in the regulation of secretory processes. In addition to being expressed in the imaginal discs, the m1.7 racGAP transcript was detected in developmentally specific germ line cells of the testes, the primary spermatocytes.
Mol Cell Biol 1992 Nov
PMID:A Drosophila rotund transcript expressed during spermatogenesis and imaginal disc morphogenesis encodes a protein which is similar to human Rac GTPase-activating (racGAP) proteins. 140 85

Induction of tyrosine phosphorylation occurs as an early and specific event in keratinocyte differentiation. A set of tyrosine-phosphorylated substrates which transduce mitogenic signals by tyrosine kinases has previously been identified. We show here that of these substrates, the Ras GTPase-activating protein, GAP, is specifically affected during calcium-induced keratinocyte differentiation. As early as 10 min after calcium addition to cultured primary mouse keratinocytes, GAP associates with tyrosine-phosphorylated proteins and translocates to the membrane. In addition, a GAP-associated protein of approximately 62 kDa (p62) becomes rapidly and heavily tyrosine phosphorylated in both membrane and cytosolic fractions. This protein corresponds to the major tyrosine-phosphorylated protein that is induced in differentiating keratinocytes as early as 5 min after calcium addition. p62 phosphorylation was not observed after exposure of these cells to epidermal growth factor, phorbol ester, or transforming growth factor beta. In contrast, PLC gamma and P13K were tyrosine phosphorylated after epidermal growth factor, but not calcium, stimulation. Thus, changes of Ras GAP and an associated p62 protein occur as early and specific events in keratinocyte differentiation and appear to involve a calcium-induced tyrosine kinase.
Mol Cell Biol 1992 Dec
PMID:Specific changes of Ras GTPase-activating protein (GAP) and a GAP-associated p62 protein during calcium-induced keratinocyte differentiation. 144 67

Activation of platelets by thrombin and other physiological agonists leads to a dramatic increase in tyrosine phosphorylation of multiple cellular proteins (Ferrell, J. E., and Martin, G. S. (1988) Mol. Cell. Biol. 8, 3606-3610; Golden, A., and Brugge, J. S. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 901-905; Nakamura, S., and Yamamura, H. (1989) J. Biol. Chem. 264, 7089-7091). To date, none of the tyrosine kinases that are involved in platelet activation, nor the substrates that are phosphorylated in response to agonists, have been identified. A "kinase trapping" strategy, designed to take advantage of the stability of known tyrosine kinase-substrate interactions, was employed to address both issues. p21rasGAP antibodies were used to examine the phosphorylated state of GAP in agonist-treated platelets and to isolate potential GAP-kinase complexes. We show that GAP and two proteins of 59 and 68 kDa are phosphorylated on tyrosine after thrombin stimulation and that three Src-related protein tyrosine kinases, Fyn, Lyn and Yes, are associated with GAP in complexes, detectable only after agonist stimulation. The thrombin-dependent detection of these kinases in GAP immunoprecipitates suggests that thrombin may either induce the formation of these complexes or activate kinases that are associated with GAP prior to, or following, agonist stimulation. This approach of "trapping" kinases bound to their substrates will be useful in identifying non-receptor tyrosine kinases involved in signaling pathways. Furthermore, although GAP phosphorylation has been previously implicated in growth factor signaling pathways, this is the first example of its involvement downstream from a G-protein-coupled receptor.
 ...
PMID:p21rasGAP association with Fyn, Lyn, and Yes in thrombin-activated platelets. 154 85

Proteins of the ras family of oncogenes have been implicated in signal transduction pathways initiated by protein kinase C (PKC) and by tyrosine kinase oncogenes and receptors, but the role that ras plays in these diverse signalling systems is poorly defined. The activity of ras proteins has been shown to be controlled in part by a cellular protein, GAP (GTPase-activating protein), that negatively regulates p21c-ras by enhancing its intrinsic GTPase activity. Thus, overexpression of GAP provides a tool for determining the step(s) in signal transduction dependent on p21c-ras activity. In this paper, we report that overexpression of GAP blocks the phorbol ester (tetradecanoyl phorbol acetate [TPA])-induced activation of p42 mitogen-activated protein kinase (p42mapk), c-fos expression, and DNA synthesis. GAP overexpression did not block responses to serum or fluoroaluminate. Moreover, not all biochemical events elicited by TPA were affected by GAP overexpression, as increased glucose uptake and phosphorylation of MARCKS, a major PKC substrate, occurred normally. Reduction of GAP expression to near normal levels restored the ability of the cells to activate p42mapk in response to TPA. These findings suggest that ras and GAP together play a key role in a PKC-dependent signal transduction pathway which leads to p42mapk activation and cell proliferation.
Mol Cell Biol 1992 Mar
PMID:Regulation of tetradecanoyl phorbol acetate-induced responses in NIH 3T3 cells by GAP, the GTPase-activating protein associated with p21c-ras. 154 25

Sec4, a GTP-binding protein of the ras superfamily, is required for exocytosis in the budding yeast Saccharomyces cerevisiae. To test the role of GTP hydrolysis in Sec4 function, we constructed a mutation, Q-79----L, analogous to the oncogenic mutation of Q-61----L in Ras, in a region of Sec4 predicted to interact with the phosphoryl group of GTP. The sec4-leu79 mutation lowers the intrinsic hydrolysis rate to unmeasurable levels. A component of a yeast lysate specifically stimulates the hydrolysis of GTP by Sec4, while the rate of hydrolysis of GTP by Sec4-Leu79 can be stimulated by this GAP activity to only 30% of the stimulated hydrolysis rate of the wild-type protein. The decreased rate of hydrolysis results in the accumulation of the Sec4-Leu79 protein in its GTP-bound form in an overproducing yeast strain. The sec4-leu79 allele can function as the sole copy of sec4 in yeast cells. However, it causes recessive, cold-sensitive growth, a slowing of invertase secretion, and accumulation of secretory vesicles and displays synthetic lethality with a subset of other secretory mutants, indicative of a partial loss of Sec4 function. While the level of Ras function reflects the absolute level of GTP-bound protein, our results suggest that the ability of Sec4 to cycle between its GTP and GDP bound forms is important for its function in vesicular transport, supporting a mechanism for Sec4 function which is distinct from that of the Ras protein.
Mol Cell Biol 1992 May
PMID:Hydrolysis of GTP by Sec4 protein plays an important role in vesicular transport and is stimulated by a GTPase-activating protein in Saccharomyces cerevisiae. 156 38

Incorporation of the available data on rac in neutrophils, CDC42 in yeast, and rho in fibroblasts suggests a general model for the function of rho-like GTPase (Figure 1). Conversion of an inactive cytoplasmic rho-related p21GDP/GDI complex to active p21. GTP occurs by inhibition of GAP and/or stimulation of exchange factors in response to cell signals. p21.GTP is then able to interact with its target at the plasma membrane. This could result in a conformational change in the target, enabling it to bind cytosolic protein(s). Alternatively, p21.GTP could be actively involved in transporting cytosolic protein(s) to the target. A GAP protein, perhaps intrinsic to the complex, would stimulate GTP hydrolysis allowing p21.GDP to dissociate. Solubilization of p21GDP by interaction with GDI would complete a cycle. What about the nature of the final complex? The rac-regulated NADPH oxidase complex in neutrophils is currently the best understood and most amenable to further biochemical analysis. Two plasma-membrane bound subunits encode the catalytic function necessary for producing superoxide, but the two cytosolic proteins, p47 and p67, are essential for activity. Why the complexity? Production of superoxide is tightly coordinated with phagocytosis, a membrane process driven by rearrangement of cortical actin. This is not unrelated to the membrane ruffling and macropinocytosis that we observe in fibroblasts microinjected with p21rac. It is tempting to speculate, therefore, that in neutrophils rac is involved not only in promoting the assembly of the NADPH oxidase but also in the coordinate reorganization of cortical actin leading to phagocytosis. For CDC42 controlled bud assembly in yeast, the components of the plasma-membrane complex are not so clear. By analogy with rac in neutrophils, it seems likely that CDC42 is involved in promoting the assembly of cytosolic components at the bud site on the plasma membrane. These putative cytosolic proteins have not yet been identified, but BEM1 and ABP1 are two possible candidates. The biochemical basis for the stimulation of adhesion plaques and actin stress fibers by p21rho in fibroblasts is also unclear. However, components of the adhesion plaque such as vinculin and talin are known to be cytosolic when not complexed with integrin receptors, and rho could be involved in regulating their assembly into the adhesion plaque. Several things are still difficult to incorporate into this model. First the target for CDC42, the bud site, although not yet structurally defined requires the activity of another small GTPase, BUD1. Similarly, in activated neutrophils, the NADPH oxidase is found in a complex with rap1, the mammalian homologue of BUD1 (BoKoch et al., 1989). It seems likely, therefore, that the target is not simply a plasma-membrane protein but may be a complex of proteins whose formation is under the control of the rap1/BUD1 GTPase. The other black box in this model is the actin connection: activation of bud assembly by CDC42 is followed by actin polymerization, activation of NADPH oxidase in neutrophils occurs concomitantly with phagocytosis, a cortical actin-dependent process, and p21rho in fibroblasts couples the formation of adhesion plaques to actin stress fibers. One possible link between the GTPase-driven assembly of a plasma-membrane complex and actin polymerization could involve the SH3 domain. Interestingly, both p47 and p67 and yeast ABP1 and BEM1 have SH3 domain. If rho-like GTPases recognize plasma-membrane targets already associated with cortical actin, then this could promote an interaction with a subset of SH3-containing proteins. The result of this would be a GTPase-regulated aggregation of a group of proteins at a single site in the plasma membrane. It is not too difficult to imagine biological processes where such a spatial integration of different biochemical activities would be essential: coupling the assembly of bud components to the formation of actin fibers in yeast; or the activation of NADPH oxidase to phagocytosis in neutrophils; or the assembly of adhesion plaques and the formation of actin stress fibers in fibroblasts are just three examples that have emerged so far. In conclusion, although rho-like GTPases clearly have distinct roles in different mammalian cell types and in yeast, their underlying mechanism of action appears to be strikingly similar. Whether this will remain so when there are some biochemical data to back up these initial observations, time will tell.
Mol Biol Cell 1992 May
PMID:Ras-related GTPases and the cytoskeleton. 161 Nov 53


1 2 3 4 5 6 7 8 9 10 Next >>