title: CiMutT, an asidian MutT homologue, has a 7, 8-dihydro-8-oxo-dGTP pyrophosphohydrolase activity responsible for sanitization of oxidized nucleotides in Ciona intestinalis.
abstract: The oxidized nucleotide precursors 7, 8-dihydro-8-oxo-dGTP (8-oxo-dGTP) and 1, 2-dihydro-2-oxo-dATP (2-oxo-dATP) are readily incorporated into nascent DNA strands during replication, which would cause base substitution mutations. E. coli MutT and human homologue hMTH1 hydrolyze 8-oxo-dGTP, thereby preventing mutations. In this study, we searched for hMTH1 homologues in the ascidian Ciona intestinalis using the NCBI-BLAST database. Among several candidates, we focused on one open reading frame, designated as CiMutT, because of its high degree of identity (41.7%) and similarity (58.3%) to the overall amino acid sequence of hMTH1, including the Nudix box. CiMutT significantly suppressed the mutator activity of E. coli mutT mutant. Purified CiMutT had a pyrophosphohydrolase activity that hydrolyzed 8-oxo-dGTP to 8-oxo-dGMP and inorganic pyrophosphate. It had a pH optimum of 9.5 and Mg(++) requirement with optimal activity at 5 mM. The activity of CiMutT for 8-oxo-dGTP was comparable to that of hMTH1, while it was 100-fold lower for 2-oxo-dATP than that of hMTH1. These facts indicate that CiMutT is a functional homologue of E. coli MutT. In addition, the enzyme hydrolyzed all four of the unoxidized nucleoside triphosphates, with a preference for dATP. The specific activity for 8-oxo-dGTP was greater than that for unoxidized dATP and dGTP. These results suggest that CiMutT has the potential to prevent mutations by 8-oxo-dGTP in C. intestinalis.
authors.affiliation: Laboratory of Stress Response Biology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Yonekura
authors.forename: U
authors.initials: U
authors.lastname: Sanada
authors.forename: Qiu-Mei
authors.initials: QM
authors.lastname: Zhang-Akiyama
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002938:Ciona intestinalis / Q000201:enzymology*; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D003838:Deoxyadenine Nucleotides / Q000378:metabolism; D003848:Deoxyguanine Nucleotides / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D011755:Pyrophosphatases / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D016415:Sequence Alignment
chemical_list: C490485:8-oxo-7,8-dihydrodeoxyguanosine diphosphate; C089930:8-oxodeoxyadenosine triphosphate; D003838:Deoxyadenine Nucleotides; D003848:Deoxyguanine Nucleotides; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; C078206:8-oxodeoxyguanosine triphosphate; D010744:Phosphoric Monoester Hydrolases; D011755:Pyrophosphatases; C052211:mutT protein, E coli; C078207:8-oxodGTPase; D045643:DNA Repair Enzymes