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)

Mannose 6-phosphate receptors (MPRs) deliver lysosomal hydrolases from the Golgi to endosomes and then return to the Golgi complex. TIP47 recognizes the cytoplasmic domains of MPRs and is required for endosome-to-Golgi transport. Here we show that TIP47 also bound directly to the Rab9 guanosine triphosphatase (GTPase) in its active, GTP-bound conformation. Moreover, Rab9 increased the affinity of TIP47 for its cargo. A functional Rab9 binding site was required for TIP47 stimulation of MPR transport in vivo. Thus, a cytosolic cargo selection device may be selectively recruited onto a specific organelle, and vesicle budding might be coupled to the presence of an active Rab GTPase.
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PMID:Role of Rab9 GTPase in facilitating receptor recruitment by TIP47. 1136 Sep 88

The Ran guanosine triphosphatase (GTPase) controls nucleocytoplasmic transport, mitotic spindle formation, and nuclear envelope assembly. These functions rely on the association of the Ran-specific exchange factor, RCC1 (regulator of chromosome condensation 1), with chromatin. We find that RCC1 binds directly to mononucleosomes and to histones H2A and H2B. RCC1 utilizes these histones to bind Xenopus sperm chromatin, and the binding of RCC1 to nucleosomes or histones stimulates the catalytic activity of RCC1. We propose that the docking of RCC1 to H2A/H2B establishes the polarity of the Ran-GTP gradient that drives nuclear envelope assembly, nuclear transport, and other nuclear events.
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PMID:Chromatin docking and exchange activity enhancement of RCC1 by histones H2A and H2B. 1137 90

The human MTH1 gene located on chromosome 7p22 consists of 5 major exons. MTH1 gene produces seven types of mRNAs and the B-type mRNAs with exon 2b-2c segments direct synthesis of three forms of MTH1 polypeptides (p22, p21, and p18) by alternative initiation of translation, while the others encode only p18. In human cells, p18, the major form is mostly localized in the cytoplasm with some in the mitochondria. A single nucleotide polymorphism (SNP) in exon 2, which is tightly liked to another SNP (GTG83/ATG83), creates an additional alternative in-frame AUG in B-type MTH1 mRNAs yielding the fourth MTH1 polypeptide, p26 that possesses an additional mitochondrial targeting signal. These SNPs are likely to be one of the risk factors for cancer or for neuronal degeneration. The 30 amino acid residues are identical between MTH1 and MutT, and there is a highly conserved region consisting of 23 residues (MTH1: Gly36 to Gly58), with 14 identical residues. A chimeric protein in which the 23 residue sequence of MTH1 was replaced with that of MutT, retains the capability to hydrolyze 8-oxo-dGTP, indicating that the 23 residue sequences of MTH1 and MutT are functionally and structurally equivalent, and constitute a functional phosphohydrolase module. Saturated mutagenesis of the module in MTH1 indicated that an amphipathic property of the alpha-helix I consisting of 14 residues of the module (Thr44 to Gly58) is essential to maintain the stable catalytic surface for 8-oxo-dGTPase. MTH1 but not MutT efficiently hydrolyzes two forms of oxidized dATP, 2-hydroxy-dATP and 8-oxo-dATP, as well as 8-oxo-dGTP and 8-oxo-GTP. Thus, MTH1 is designated as the oxidized purine nucleoside triphosphatase and has a much wider substrate specificity than MutT. There is a significant homology between MTH1 protein and the C-terminal half of human MYH protein, which may be involved in the recognition of 8-oxoguanine and 2-hydroxyadenine.
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PMID:Molecular genetics and structural biology of human MutT homolog, MTH1. 1137 87

The regulators of G-protein signaling (RGS) proteins accelerate the intrinsic guanosine triphosphatase activity of heterotrimeric G-protein alpha subunits and are thus recognized as key modulators of G-protein-coupled receptor signaling. RGS12 and RGS14 contain not only the hallmark RGS box responsible for GTPase-accelerating activity but also a single G alpha(i/o)-Loco (GoLoco) motif predicted to represent a second G alpha interaction site. Here, we describe functional characterization of the GoLoco motif regions of RGS12 and RGS14. Both regions interact exclusively with G alpha(i1), G alpha(i2), and G alpha(i3) in their GDP-bound forms. In GTP gamma S binding assays, both regions exhibit guanine nucleotide dissociation inhibitor (GDI) activity, inhibiting the rate of exchange of GDP for GTP by G alpha(i1). Both regions also stabilize G alpha(i1) in its GDP-bound form, inhibiting the increase in intrinsic tryptophan fluorescence stimulated by AlF(4)(-). Our results indicate that both RGS12 and RGS14 harbor two distinctly different G alpha interaction sites: a previously recognized N-terminal RGS box possessing G alpha(i/o) GAP activity and a C-terminal GoLoco region exhibiting G alpha(i) GDI activity. The presence of two, independent G alpha interaction sites suggests that RGS12 and RGS14 participate in a complex coordination of G-protein signaling beyond simple G alpha GAP activity.
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PMID:RGS12 and RGS14 GoLoco motifs are G alpha(i) interaction sites with guanine nucleotide dissociation inhibitor Activity. 1138 33

The predicted ORF3 polypeptide (Orf3p) of the linear genetic element pGKL2 from Kluyveromyces lactis was expressed in Bacillus megaterium as a fusion protein with a His(6X)-tag at the C-terminus for isolation by Ni-affinity chromatography. This is the first time that a yeast cytoplasmic gene product has been expressed heterologously as a functional protein in a bacterial system. The purified protein was found to display both RNA 5'-triphosphatase and guanylyltransferase activities. When the lysine residue present at position 177 of the protein within the sequence motif (KXDG), highly conserved in capping enzymes and other nucleotidyl transferases, was substituted by alanine, the guanylyltransferase activity was lost, thereby proving an important role for the transfer of GMP from GTP to the 5'-diphosphate end of the mRNA. Our in vitro data provides the first direct evidence that the polypeptide encoded by ORF3 of the cytoplasmic yeast plasmid pGKL2 functions as a plasmid-specific capping enzyme. Since genes equivalent to ORF3 of pGKL2 have been identified in all autonomous cytoplasmic yeast DNA elements investigated so far, our findings are of general significance for these widely distributed yeast extranuclear genetic elements.
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PMID:Kluyveromyces lactis cytoplasmic plasmid pGKL2: heterologous expression of Orf3p and proof of guanylyltransferase and mRNA-triphosphatase activities. 1142 64

A nucleoside triphosphatase (NTPase) present in highly purified preparations of pea nuclei was partially characterized. The activity of this enzyme was stimulated by divalent cations (Mg2+ = Mn2+ > Ca2+), but was not affected by the monovalent cations, Na+ and K+. The Mg(2+)-dependent activity was further stimulated by concentrations of Ca2+ in the low micromolar range. It could catalyze the hydrolysis of ATP, GTP, UTP, and CTP, all with a pH optimum of 7.5. The nuclear NTPase activity was not inhibited by vanadate, oligomycin, or nitrate, but was inhibited by relatively low concentrations of quercetin and the calmodulin inhibitor, compound 48/80. The NTPase was stimulated more than 50% by red light, and this effect was reversed by subsequent irradiation with far-red light. The photoreversibility of the stimulation indicated that the photoreceptor for this response was phytochrome, an important regulator of photomorphogenesis and gene expression in plants.
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PMID:Characterization of nucleoside triphosphatase activity in isolated pea nuclei and its photoreversible regulation by light. 1153 60

Heterotrimeric GTP-binding proteins (G proteins) control cellular functions by transducing signals from the outside to the inside of cells. Regulator of G protein signaling (RGS) proteins are key modulators of the amplitude and duration of G protein-mediated signaling through their ability to serve as guanosine triphosphatase-activating proteins (GAPs). We have identified RGS-PX1, a Galpha(s)-specific GAP. The RGS domain of RGS-PX1 specifically interacted with Galpha(s), accelerated its GTP hydrolysis, and attenuated Galpha(s)-mediated signaling. RGS-PX1 also contains a Phox (PX) domain that resembles those in sorting nexin (SNX) proteins. Expression of RGS-PX1 delayed lysosomal degradation of the EGF receptor. Because of its bifunctional role as both a GAP and a SNX, RGS-PX1 may link heterotrimeric G protein signaling and vesicular trafficking.
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PMID:RGS-PX1, a GAP for GalphaS and sorting nexin in vesicular trafficking. 1172 93

A review of the meeting "The Ras Superfamily of Small GTP-Binding Proteins," FASEB Summer Research Conference, Snowmass, Colorado, 15 through 20 July 2000 The molecular cloning of the human proto-oncogene encoding Ras was reported nearly 20 years ago. Since then, Ras has become the prototypical member of a superfamily of small guanosine triphosphatase proteins. Despite the maturity of this field of research, the discovery of new functions and interactions between the superfamily members continues unabated. Symons and Takai have written a meeting report on the latest findings on the Ras superfamily.
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PMID:Ras GTPases: singing in tune. 1175 38

FtsZ, the major cytoskeletal component of the bacterial cell-division machine, assembles into a ring (the Z-ring) that contracts at septation. FtsZ is a bacterial homolog of tubulin, with similar tertiary structure, GTP hydrolysis, and in vitro assembly. We used green fluorescent protein-labeled FtsZ and fluorescence recovery after photobleaching to show that the E. coli Z-ring is extremely dynamic, continually remodeling itself with a half-time of 30 s. ZipA, a membrane protein involved in cell division that colocalizes with FtsZ, was equally dynamic. The Z-ring of the mutant ftsZ84, which has 1/10 the guanosine triphosphatase activity of wild-type FtsZ in vitro, showed a 9-fold slower turnover in vivo. This finding implies that assembly dynamics are determined primarily by GTP hydrolysis. Despite the greatly reduced assembly dynamics, the ftsZ84 cells divide with a normal cell-cycle time.
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PMID:Rapid assembly dynamics of the Escherichia coli FtsZ-ring demonstrated by fluorescence recovery after photobleaching. 1185 62

The multidrug resistance proteins P-glycoprotein (Pgp) and MRP1 are drug-efflux pumps. In this study, we compared the nucleotide triphosphatase activities of the isolated N-terminal nucleotide binding domains (NBD1) of Pgp and MRP1, and explored the potential role of the phosphorylation target domain of Pgp on the regulation of Pgp NBD1 ATPase activity. We found that: (1) the NBD1s of Pgp and MRP1 have ATPase and GTPase activities, (2) the K(m)s of Pgp NBD1 for ATP and GTP hydrolysis are identical, while the K(m) of MRP1 NBD1 for ATP is lower than that for GTP, and (3) phosphorylation of MLD by PKA or PKC produces a marginal increase of V(max) for ATP hydrolysis, without affecting the affinity for ATP. These results show efficient GTP hydrolysis by the NBD1s of Pgp and MRP1, and a minor role of phosphorylation in the control of Pgp NBD1 ATPase activity.
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PMID:Nucleotide triphosphatase activity of the N-terminal nucleotide-binding domains of the multidrug resistance proteins P-glycoprotein and MRP1. 1216 30


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