2003 Fiscal Year Final Research Report Summary
A novel mechanism for preventing mutations caused by oxidation of guanine nucleotides
| Project/Area Number |
14580687
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Molecular biology
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| Research Institution | Fukuoka Dental College |
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Principal Investigator |
TAKAGI Yasumitsu Fukuoka Dental College, Dep. of Dentistry, Associate Professor, 歯学部, 助教授 (20212003)
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| Co-Investigator(Kenkyū-buntansha) |
SEKIGUCHI Mutsuo Fukuoka Dental College, Institute for, Director, 所長 (00037342)
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| Project Period (FY) |
2002 – 2003
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| Keywords | DNA repair / DNA oxidation / Spontaneous mutation / oxidation of guanine nucleotides / Spontaneous carcinogenesis |
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| Research Abstract |
MutT-related proteins degrade 8-oxo-7,8-dihydrodeoxyguanosine triphosphate (8-oxo-dGTP), a mutagenic substrate for DNA synthesis, in the nucleotide pool, thereby preventing DNA replication errors. During a search of GenBank EST database, we found a new member of MutT-related protein, MTH2, which possesses the 23-amino acid MutT module. The cloned mouse MTH2 (mMTH2) cDNA was expressed in Escherichia coli mutT(-) cells and the protein was purified. mMTH2 protein hydrolyzes 8-oxo-dGTP to 8-oxo-dGMP, with Km of 32&mgr;M. Expression of cDNA for mMTH2 reduced significantly the elevated level of spontaneous mutation frequency of E. coli mutT(-) cells. Thus, MTH2 has a potential to protect the genetic material from the untoward effects of endogenous oxygen radicals. MTH2 could act as an MTH1 redundancy factor.
Also, we reported that human cells have another mechanism for cleaning up the nucleotide pool to ensure accurate DNA replication. The human Nudix type 5 (NUDT5) protein hydrolyses 8-oxo-dGDP to monophosphate with a K(m) of 0.77 microM, a value considerably lower than that for ADP sugars, which were originally identified as being substrates of NUDT5. NUDT5 hydrolyses 8-oxo-dGTP only at very low levels, but is able to substitute for MutT when it is defective. When NUDT5 is expressed in E. coli mutT(-) cells, the increased frequency of spontaneous mutations is decreased to normal levels. Considering the enzymatic parameters of MTH1 and NUDT5 for oxidized guanine nucleotides, NUDT5 might have a much greater role than MTH1 in preventing the occurrence of mutations that are caused by the misincorporation of 8-oxoguanine in human cells.
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[Publications] Takagi, Y., Takahashi, M., Sanada, M., Ito, R., Yamaizumi, M., Sekiguchi, M.: "Roles of MGMT and MLH1 proteins in alkylation-induced apoptosis and mutagenesis."DNA Repair. 2. 1135-1146 (2003)
Description
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