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

8-Oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is produced during cellular metabolism, and its misincorporation into DNA causes mutation. Human cells possess an enzyme that hydrolyzes 8-oxo-dGTP to the corresponding nucleoside monophosphate, thereby preventing misincorporation of 8-oxo-7,8-dihydroguanine into DNA. Sequence analyses of the MTH1 gene, encoding the 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphatase (8-oxo-dGTPase) protein in human cell lines revealed that a G to A base substitution frequently occurs at codon 83, which causes a change of valine to methionine in the MTH1 protein [Wu, C. et al., Biochem. Biophys. Res. Commun. 214 (1995) 1239-1245]. Here we isolated cDNAs for the two types of MTH1 protein and expressed them in Escherichia coli mutT-. cells, devoid of their own 8-oxo-dGTPase activity. The two forms of proteins were purified to physical homogeneity, and amino acid analyses confirmed that the variant protein, Met83-MTH1, indeed carries the corresponding amino acid substitution. Met83-MTH1, but not normal type Val83-MTH1, was separated into two peaks in hydrophobic interacting chromatography. 8-Oxo-dGTPase activity of Met83-MTH1 is more thermolabile than that of Val83-MTH1. Circular dichroism (CD) and fluorescence spectroscopic analyses confirmed this conclusion. CD further indicated that Met83-MTH1 has a higher alpha-helix content.
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PMID:Biochemical and physicochemical characterization of normal and variant forms of human MTH1 protein with antimutagenic activity. 933 Jun 14

Cet1, the RNA triphosphatase component of the yeast mRNA capping apparatus, catalyzes metal-dependent gamma-phosphate hydrolysis within the hydrophilic interior of an eight-strand beta barrel (the "triphosphate tunnel"), which rests upon a globular protein core (the "pedestal"). We performed a structure-guided alanine scan of 17 residues located in the tunnel (Ser(373), Thr(375), Gln(405), His(411), Ser(429), Glu(488), Thr(490)), on the tunnel's outer surface (Ser(378), Ser(487), Thr(489), His(491)), at the tunnel-pedestal interface (Ile(304), Met(308)) and in the pedestal (Asp(315), Lys(317), Arg(321), Asp(425)). Alanine mutations at 14 positions had no significant effect on Cet1 phosphohydrolase activity in vitro and had no effect on Cet1 function in vivo. Two of the mutations (R321A and D425A) elicited a thermosensitive (ts) yeast growth phenotype. The R321A and D425A proteins had full phosphohydrolase activity in vitro, but were profoundly thermolabile. Arg(321) and Asp(425) interact to form a salt bridge within the pedestal that tethers two of the strands of the tunnel. Mutations R321Q and D411N resulted in ts defects in vivo and in vitro, as did the double-mutant R321A-D435A, whereas the R321K protein was fully stable in vivo and in vitro. These results highlight the critical role of the buried salt bridge in Cet1 stability. Replacement of Ser(429) by alanine or valine elicited a cold-sensitive (cs) yeast growth phenotype. The S429A and S429V proteins were fully active when produced in bacteria at 37 degrees C, but were inactive when produced at 17 degrees C. Replacement of Ser(429) by threonine partially suppressed the cold sensitivity of the Cet1 phosphohydrolase, but did not suppress the cs growth defect in yeast.
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PMID:Functional groups required for the stability of yeast RNA triphosphatase in vitro and in vivo. 1139 22