5jxy
From Proteopedia
Enzyme-substrate complex of TDG catalytic domain bound to a G/U analog
Structural highlights
Function[TDG_HUMAN] In the DNA of higher eukaryotes, hydrolytic deamination of 5-methylcytosine to thymine leads to the formation of G/T mismatches. This enzyme corrects G/T mispairs to G/C pairs. It is capable of hydrolyzing the carbon-nitrogen bond between the sugar-phosphate backbone of the DNA and a mispaired thymine. In addition to the G/T, it can remove thymine also from C/T and T/T mispairs in the order G/T >> C/T > T/T. It has no detectable activity on apyrimidinic sites and does not catalyze the removal of thymine from A/T pairs or from single-stranded DNA. It can also remove uracil and 5-bromouracil from mispairs with guanine. Publication Abstract from PubMedThymine DNA Glycosylase (TDG) is a base excision repair enzyme functioning in DNA repair and epigenetic regulation. TDG removes thymine from mutagenic G.T mispairs arising from deamination of 5-methylcytosine (mC), and it processes other deamination-derived lesions including uracil (U). Essential for DNA demethylation, TDG excises 5-formylcytosine and 5-carboxylcytosine, derivatives of mC generated by Tet (ten-eleven translocation) enzymes. Here, we report structural and functional studies of TDG82-308, a new construct containing 29 more N-terminal residues than TDG111-308, the construct used for previous structures of DNA-bound TDG. Crystal structures and NMR experiments demonstrate that most of these N-terminal residues are disordered, for substrate- or product-bound TDG82-308 Nevertheless, G.T substrate affinity and glycosylase activity of TDG82-308 greatly exceeds that of TDG111-308 and is equivalent to full-length TDG. We report the first high-resolution structures of TDG in an enzyme-substrate complex, for G.U bound to TDG82-308 (1.54 A) and TDG111-308 (1.71 A), revealing new enzyme-substrate contacts, direct and water-mediated. We also report a structure of the TDG82-308 product complex (1.70 A). TDG82-308 forms unique enzyme-DNA interactions, supporting its value for structure-function studies. The results advance understanding of how TDG recognizes and removes modified bases from DNA, particularly those resulting from deamination. Structural basis of damage recognition by thymine DNA glycosylase: Key roles for N-terminal residues.,Coey CT, Malik SS, Pidugu LS, Varney KM, Pozharski E, Drohat AC Nucleic Acids Res. 2016 Aug 31. pii: gkw768. PMID:27580719[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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