Purification and characterization of a mammalian homolog of Escherichia coli MutY mismatch repair protein from calf liver mitochondria

A protein homologous to the Escherichia coli MutY glycosylase, referred to as mtMYH, has been purified from calf liver mitochondria. SDS–polyacrylamide gel electrophoresis, western blot analysis as well as gel filtration chromatography predicted the molecular mass of the purified calf mtMYH to be 35–40 kDa. Gel mobility shift analysis showed that the purified mtMYH formed specific binding complexes with A/8-oxoG, G/8-oxoG and T/8-oxoG, weakly with C/8-oxoG, but not with A/G and A/C mismatches. The purified mtMYH exhibited DNA glycosylase activity removing adenine mispaired with G, C or 8-oxoG and weakly removing guanine mispaired with 8-oxoG. The mtMYH glycosylase activity was insensitive to high concentrations of NaCl and EDTA. The purified mtMYH cross-reacted with antibodies against both intact MutY and a peptide of human MutY homolog (hMYH). DNA glycosylase activity of mtMYH was inhibited by anti-MutY antibodies but not by anti-hMYH peptide antibodies. Together with the previously described mitochondrial MutT homolog (MTH1) and 8-oxoG glycosylase (OGG1, a functional MutM homolog), mtMYH can protect mitochondrial DNA from the mutagenic effects of 8-oxoG.