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Mouse MTH1 protein with 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphatase activity that prevents transversion

T Kakuma1, J Nishida, T Tsuzuki

  • 1Department of Biochemistry, Kyushu University, Fukuoka, Japan.

The Journal of Biological Chemistry
|October 27, 1995
PubMed

Insights

This study identifies and characterizes mouse 8-oxo-dGTPase, an enzyme crucial for preventing mutations caused by 8-oxo-dGTP. Its expression in E. coli mutT- mutant cells restored normal mutation frequency, highlighting its protective role.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • 8-Oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is a DNA-damaging metabolite formed during normal cellular metabolism.
  • Incorporation of 8-oxo-dGTP into DNA leads to mutations, necessitating cellular repair mechanisms.
  • 8-oxo-dGTPase is an enzyme responsible for degrading 8-oxo-dGTP, preventing its mutagenic effects.

Purpose of the Study:

  • To isolate and characterize the cDNA for mouse 8-oxo-dGTPase.
  • To investigate the functional role of mouse 8-oxo-dGTPase in preventing DNA mutations.
  • To determine the tissue distribution of 8-oxo-dGTPase activity in mice.

Main Methods:

  • Isolation of mouse 8-oxo-dGTPase cDNA using human MTH1 cDNA as a probe.
  • Nucleotide sequencing to determine the protein sequence and molecular weight.
  • Expression of mouse 8-oxo-dGTPase in E. coli mutT- mutant cells.
  • Measurement of spontaneous mutation frequency in engineered E. coli cells.
  • Enzyme activity assays across various mouse tissues.

Main Results:

  • The nucleotide sequence revealed mouse 8-oxo-dGTPase (MTH1 protein) consists of 156 amino acid residues with a molecular weight of 17,896.
  • Expression of mouse 8-oxo-dGTPase in E. coli mutT- mutant cells produced an 18-kDa protein.
  • The functional expression of mouse 8-oxo-dGTPase in mutant E. coli cells restored normal spontaneous mutation frequency.
  • High 8-oxo-dGTPase activity was detected in liver, thymus, and large intestine, with lower levels in other organs.
  • Embryonic stem cells exhibited exceptionally high levels of 8-oxo-dGTPase activity.

Conclusions:

  • Mouse 8-oxo-dGTPase, homologous to human MTH1, effectively degrades 8-oxo-dGTP.
  • The enzyme plays a critical role in maintaining genomic stability by preventing mutations.
  • Tissue-specific expression patterns suggest specialized roles in organs with high cell turnover or exposure to oxidative stress.

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