Catalytic role of escherichia cou muty gene product in dna mismatch repair

MutY recognizes and removes the undamaged adenine mispaired with guanine, cytosine, 8-oxoguanine or 8-oxoadenine. In vitro studies have also shown that MutY removes adenine analogs when they are misincorporated opposite guanine in duplex DNA. In this study, synthetic oligonucleotide duplexes containing adenine opposite guanine or 8oxoguanine, and adenine analogs (nebularine, 2-aminopurine or inosine) paired with guanine were used to assay mismatch repair activity of intact MutY and the N-terminal 26 kDa domain of MutY (Metl to Lys225), generated by controlled proteolysis with trypsin. Kinetic studies indicate that MutY and the truncated p26 domain have the highest activity on a substrate where nebularine is substituted for adenine and paired with guanine . Removal of 125 amino acids at the C-terminus (Gln226Val350) of MutY did not compromise the DNA binding activity, although this domain showed reduced catalytic activity. This result also demonstrates that the critical amino acid residues participating in substrate binding and catalysis are present in the N-terminal p26 domain. There have been mixed reports on the catalytic role of MutY. Some studies claim that MutY is purely an adenine glycosylase, while others have detected different levels of AP lyase activity accompanying the glycosylase activity. Our studies with MutY and the truncated p26 domain of MutY, unequivocally establishes that the incision of the phosphodiester bond follows the hydrolysis of the N-elvcosvlic bond and MutY catalyzes both the above activities concomitantly.