Structural basis for removal of adenine mispaired with 8-oxoguanine by MutY adenine DNA glycosylase.

The genomes of aerobic organisms suffer chronic oxidation of guanine to the genotoxic product 8-oxoguanine (oxoG). Replicative DNA polymerases misread oxoG residues and insert adenine instead of cytosine opposite the oxidized base. Both bases in the resulting AoxoG mispair are mutagenic lesions, and both must undergo base-specific replacement to restore the original CG pair. Doing so represents a formidable challenge to the DNA repair machinery, because adenine makes up roughly 25% of the bases in most genomes. The evolutionarily conserved enzyme adenine DNA glycosylase (called MutY in bacteria and hMYH in humans) initiates repair of AoxoG to CG by removing the inappropriately paired adenine base from the DNA backbone. A central issue concerning MutY function is the mechanism by which AoxoG mispairs are targeted among the vast excess of AT pairs. Here we report the use of disulphide crosslinking to obtain high-resolution crystal structures of MutY-DNA lesion-recognition complexes. These structures reveal the basis for recognizing both lesions in the A*oxoG pair and for catalysing removal of the adenine base.