Structural Basis for Finding OG Lesions and Avoiding Undamaged G by the DNA Glycosylase MutY

Abstract

The adenine glycosylase MutY selectively initiates repair of OG:A lesions and, by comparison, avoids G:A mispairs. The ability to distinguish these closely related substrates relies on the C-terminal domain of MutY, which structurally resembles MutT. To understand the mechanism for substrate specificity, we crystallized MutY in complex with DNA containing G across from the high-affinity azaribose transition state analogue. Our structure shows that G is accommodated by the OG site and highlights the role of a serine residue in OG versus G discrimination. The functional significance of Ser308 and its neighboring residues was evaluated by mutational analysis, revealing the critical importance of a β loop in the C-terminal domain for mutation suppression in cells, and biochemical performance <i>in vitro</i>. This loop comprising residues Phe307, Ser308, and His309 (<i>Geobacillus stearothermophilus</i> sequence positions) is conserved in MutY but absent in MutT and other DNA repair enzymes and may therefore serve as a MutY-specific target exploitable by chemical biological probes.