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Structural basis for excision of deaminated and oxidized 5‐methylcytosine by thymine DNA glycosylase
Author(s) -
Maiti Atanu,
Pozharski Edwin,
Drohat Alexander C
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.539.10
Subject(s) - dna glycosylase , dna demethylation , base excision repair , 5 methylcytosine , dna repair , dna , alkb , dna damage , biochemistry , biology , ap endonuclease , cytosine , deamination , chemistry , microbiology and biotechnology , enzyme , gene , dna methylation , gene expression
The DNA base excision repair (BER) pathway is essential for maintaining genomic integrity and is implicated in active DNA demethylation, a key element of epigenetic transcriptional regulation. Thymine DNA glycosylase (TDG) excises thymine from mutagenic G·T mispairs, initiating repair of deaminated 5‐methylcytosine (mC). TDG also excises 5‐formylcytosine (fC) and 5‐carboxylcytosine (caC), oxidation products of mC produced by Tet enzymes. These seemingly disparate activities are consistent with TDG specificity for acting at CpG sites and its essential role in active DNA demethylation and embryonic development. Understanding how glycosylases excise lesions and avoid acting on undamaged DNA is an important problem in DNA repair. Structural and biochemical results here reveal how TDG attains broad specificity for G·T and G·fC lesions while avoiding A·T pairs. A crystal structure of TDG (catalytic domain) bound to substrate analogue suggests G·T glycosylase activity is suboptimal owing to unfavorable interactions between flipped dT substrate and two active‐site residues. Remarkably, mutating these residues greatly increases G·T activity and confers substantial activity for normal A·T base pairs. The results suggest TDG evolved with suboptimal G·T repair capability in order to minimize aberrant activity on undamaged DNA, an unprecedented finding for a repair enzyme. Supported by NIH (R01‐GM072711).