Amino acid residues involved in substrate recognition of the Escherichia coli Orf135 protein.

The Escherichia coli Orf135 protein, a MutT-type enzyme, hydrolyzes mutagenic 2-hydroxy-dATP (2-OH-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. To identify the amino acid residues that interact with these nucleotides, the Glu-33, Arg-72, Arg-77, and Asp-118 residues of Orf135, which are candidates for residues interacting with the base, were substituted, and the enzymatic activities of these mutant proteins were examined. The mutant proteins with a substitution at the 33rd, 72nd, and 118th amino acid residues displayed activities affected to various degrees for each substrate, suggesting the involvement of these residues in substrate binding. On the other hand, the mutant protein with a substitution at the 77th Arg residue had activitiy similar to that of the wild-type protein, excluding the possibility that this Arg side chain is involved in base recognition. In addition, the expression of some Orf135 mutants in orf135(-) E. coli reduced the level of formation of rpoB mutants elicited by H(2)O(2). These results reveal the residues involved in the substrate binding of the E. coli Orf135 protein.

Cancer pharmacogenomics: international trends.

It is well known that inter-individual variability exists in the responses to many drugs. Many nongenetic factors, such as age, sex, diet, and organ function, are known to affect the therapeutic effects of drugs. However, recent advances in pharmacogenomics have revealed that genetic polymorphisms also significantly influence both the efficacy and the toxicity of drugs. Mutations in the genes encoding drug-metabolizing enzymes, transporters, and target molecules may alter their expression, activity, or affinity to drugs, thereby influencing the drugs' pharmacokinetics and pharmacodynamics. Numerous studies have reported on the correlations between therapeutic outcomes and polymorphisms in drug-metabolizing enzymes, transporters, target molecules, and DNA repair enzymes. These pharmacogenomic discoveries are expected to be useful for the individualization and optimization of cancer chemotherapy.

Important amino acids in the phosphohydrolase module of Escherichia coli Orf135.

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.

Mutagenesis by damaged deoxyribonucleotides and its prevention by MutT-type hydrolyzing enzymes.

Oxidized deoxyribonucleotides, 2-hydroxydeoxyadenosine 5'-triphosphate (2-OH-dATP) and 8-hydroxydeoxyguanosine 5'-triphosphate (8-OH-dGTP), were introduced into Escherichia coli strains deficient in DNA polymerase IV (a Y-family DNA polymerase encoded in the dinB gene), and the MutT and Orfl35 proteins to examine their in vivo roles in mutagenesis elicited by 2-OH-dATP and 8-OH-dGTP. 2-OH-dATP elicited mutations less efficiently in the dinB- strain than in the wild type strain, suggesting involvement of DNA polymerase IV in 2-OH-dATP-induced mutations. 8-OH-dGTP and 2-OH-dATP elicited mutations more efficiently in mutT- and orfl35- strains, respectively, than those in their isogenic mutT+ and orfl35+ strains. These results indicate that these proteins play important roles in mutagenesis induced by 2-OH-dATP and 8-OH-dGTP in vivo.

Suppression of spontaneous and hydrogen peroxide-induced mutations by a MutT-type nucleotide pool sanitization enzyme, the Escherichia coli Orf135 protein.

BACKGROUND: We recently found that the Escherichia coli Orf135 protein, a MutT-type enzyme, hydrolysed 2-hydroxy-dATP (2-OH-dATP), and less efficiently, 8-hydroxy-dGTP. RESULTS: In this study, we examined the effects of the absence of the orf135 gene. Frequencies of spontaneous and H2O2-induced mutations were two- to three-fold higher in the orf135- strain than in the wild-type strain. These mutations include various mutations involving a G:C-->T:A transversion, the same type of mutation elicited by 2-OH-dATP. Over-expression of the Orf135 protein suppressed mutations even in the wild-type strain, as well as in the orf135- strain. CONCLUSIONS: The mutator phenotype of bacteria lacking the Orf135 protein suggests that this protein is involved in the suppression of mutations induced by oxidized deoxynucleotides in vivo and that various MutT-type enzymes contribute to nucleotide pool sanitization.