Identification of general acid catalyst for the ATPase activity of Lynch syndrome-related MutL homologs

Mutations of mismatch repair MutL homologs are causative of a hereditary cancer, Lynch syndrome. Investigation of MutL facilitates genetic diagnoses essential for cancer risk managements and therapies. We characterized MutL homologs from human and a hyperthermophile, Aquifex aeolicus, (aqMutL) to reveal the catalytic mechanism for the ATPase activity. Although existence of a general acid catalyst had not been conceived in the mechanism, analysis of the pH dependence of the aqMutL ATPase activity revealed that the reaction is accelerated by general acid-base catalysis. Analyses of mutant aqMutLs showed that Lys79 is the general acid, and the corresponding residues were confirmed to be critical for activities of human homologs, on the basis of which a catalytic mechanism for MutL ATPase is proposed. These and other results described here would contribute to evaluating the pathogenicity of Lynch syndrome-associated missense mutations.