A dimeric mechanism for contextual target recognition by Muty glycosylase

MutY, an adenine glycosylase, initiates the critical repair of an adenine:8-oxo-guanine base pair in DNA arising from polymerase error at the oxidatively damaged guanine. Here we demonstrate for the first time, using presteady-state active site titrations, that MutY assembles into a dimer upon binding substrate DNA and that the dimer is the functionally active form of the enzyme. Additionally, we observed allosteric inhibition of glycosylase activity in the dimer by the concurrent binding of two lesion mispairs. Active site titration results were independently verified by gel mobility shift assays and quantitative DNA footprint titrations. A model is proposed for the potential functional role of the observed polysteric and allosteric regulation in recruiting and coordinating interactions with the methyl-directed mismatch repair system.