title: Important amino acids in the phosphohydrolase module of Escherichia coli Orf135.
abstract: The Escherichia coli Orf135 protein, a MutT-type enzyme, hydrolyzes 2-hydroxy-dATP and 8-hydroxy-dGTP, in addition to dCTP and 5-methyl-dCTP, and its deficiency causes increases in both the spontaneous and H(2)O(2)-induced mutation frequencies. In this study, the Gly-36, Gly-37, Lys-38, Glu-43, Arg-51, Glu-52, Leu-53, Glu-55, and Glu-56 residues of Orf135, which are conserved in the three MutT-type proteins (Orf135, MutT, and MTH1), were substituted, and the enzymatic activity of these mutant proteins was examined. The mutant proteins with a substitution at the 36th, 37th, 52nd, and 56th amino acid residues completely lost their activity. On the other hand, the mutant proteins with a substitution at the 38th, 43rd, 51st, 53rd, and 55th residues could hydrolyze 5-methyl-dCTP. Some mutants with detectable activity for 5-methyl-dCTP did not hydrolyze dCTP. Activities for known substrates (5-methyl-dCTP, dCTP, 2-hydroxy-dATP, and 8-hydroxy-dGTP) were examined in detail with the four mutants, K38R, E43A, L53A, and E55Q. These results indicate the essential residues for the activity of the Orf135 protein.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Kita-ku, Sapporo 060-0812, Japan. hirokam@pharm.hokudai.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kamiya
authors.forename: Emiko
authors.initials: E
authors.lastname: Iida
authors.forename: Hideyoshi
authors.initials: H
authors.lastname: Harashima
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000378:metabolism; D003854:Deoxyribonucleotides / Q000737:chemistry*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006867:Hydrolases / Q000737:chemistry / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017553:Phosphorus Compounds / Q000737:chemistry / Q000378:metabolism; D015202:Protein Engineering / Q000379:methods; D011755:Pyrophosphatases / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D000096964:Nudix Hydrolases
chemical_list: D000596:Amino Acids; D003854:Deoxyribonucleotides; D006867:Hydrolases; D017553:Phosphorus Compounds; D011755:Pyrophosphatases; D011994:Recombinant Proteins; C422942:nudix hydrolase Orf135; D000096964:Nudix Hydrolases