Thymine DNA glycosylase specifically recognizes 5-carboxylcytosine-modified DNA

Abstract

X-ray crystallographic analysis of thymine DNA glycosylase (TDG) in complex with DNA containing 5-carboxylcytosine (5caC) analogs reveals that 5caC is a preferred substrate of TDG, providing support for a 5-methylcytosine demethylation pathway involving 5-methylcytosine oxidation and removal by base-excision repair glycosylases. Human thymine DNA glycosylase (hTDG) efficiently excises 5-carboxylcytosine (5caC), a key oxidation product of 5-methylcytosine in genomic DNA, in a recently discovered cytosine demethylation pathway. We present here the crystal structures of the hTDG catalytic domain in complex with duplex DNA containing either 5caC or a fluorinated analog. These structures, together with biochemical and computational analyses, reveal that 5caC is specifically recognized in the active site of hTDG, supporting the role of TDG in mammalian 5-methylcytosine demethylation.