Characterization of 2-hydroxyadenine DNA glycosylase activity of Escherichia coli MutY protein

Purpose: 2-Hydroxyadenine (2-ohA) is an oxidation product of adenine generated in DNA by ionizing radiation and various chemical oxidants. 2-ohA has mutational potential comparable to that of 8-oxoguanine in bacteria and mammalian cells. Recent studies have shown that 2-ohA is removed from DNA by a human MutY homolog, MYH protein, in vitro. On the other hand, the repair mechanisms for 2-ohA in Escherichia coli are not yet understood. Materials and methods: Gel shift assays were used to assess the binding activity of E. coli full-length MutY protein and its N-terminal (residues 1-226) domain (M25) to 2-ohA/G-, 2-ohA/A-, 2-ohA/C- and 2-ohA/T-containing 24-mer oligonucleotides. Furthermore, whether these proteins specifically cleave 2-ohA-containing duplex oligonucleotides was examined. Results: The purified MutY and M25 proteins had similar binding affinities to 2-ohA/G-, 2-ohA/A- and 2-ohA/C- containing oligonucleotides. MutY protein removed 2-ohA preferentially from 2-ohA/ G mispairs. M25 protein showed the reduced catalytic activity for 2-ohA/ G- containing oligonucleotides. Conclusions: E. coli MutY protein has a DNA glycosylase activity that removes 2-ohA from 2-ohA/ G mispairs in DNA. The C-terminal domain is required for the removal of 2-ohA from DNA, but is not crucial for binding to 2-ohA-containing oligonucleotides.