Structural basis for enzymatic excision of N1-methyladenine and N3-methylcytosine from DNA

Abstract

N1-methyladenine (m1A) and N3- methylcytosine (m3C) are major toxic and mutagenic lesions induced by alkylation in single-stranded DNA. In bacteria and mammals, m1A and m3C were recently shown to be repaired by AlkB-mediated oxidative demethylation, a direct DNA damage reversal mechanism. No AlkB gene homologues have been identified in Archaea. We report that m1A and m 3C are repaired by the AfAlkA base excision repair glycosylase of Archaeoglobus fulgidus, suggesting a different repair mechanism for these lesions in the third domain of life. In addition, AfAlkA was found to effect a robust excision of 1,N6-ethenoadenine. We present a high-resolution crystal structure of AfAlkA, which, together with the characterization of several site-directed mutants, forms a molecular rationalization for the newly discovered base excision activity. © 2007 European Molecular Biology Organization | All Rights Reserved.