Structural and mutation studies of two DNA demethylation related glycosylases: MBD4 and TDG.

• Type of Material: Article
• Authors: Hideharu Hashimoto, Emory University
• Language: English
• Date: 2014-08-18
• Publisher: Japan Science and Technology Agency
• Publication Version: Final Published Version
• Copyright Statement: Copyright ©2014 The Biophysical Society of Japan
• Final Published Version (URL): http://dx.doi.org/10.2142/biophysics.10.63
• Title of Journal or Parent Work: Biophysics (Nagoya-shi)
• Volume: 10
• Issue: 0
• Start Page: 63
• End Page: 68
• Keywords: active demethylation; Thymine DNA Glycosylase; DNA glycosylase; methyl-CpG binding domain 4
• Research Categories: Biology, Microbiology; Health Sciences, Immunology

Abstract

Two mammalian DNA glycosylases, methyl-CpG binding domain protein 4 (MBD4) and thymine DNA glycosylase (TDG), are involved in active DNA demethylation via the base excision repair pathway. Both MBD4 and TDG excise the mismatch base from G:X, where X is uracil, thymine, and 5-hydroxymethyluracil (5hmU). In addition, TDG excises 5mC oxidized bases i.e. when X is 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) not 5-hydroxymethylcytosine (5hmC). A MBD4 inactive mutant and substrate crystal structure clearly explains how MBD4 glycosylase discriminates substrates: 5mC are not able to be directly excised, but a deamination process from 5mC to thymine is required. On the other hand, TDG is much more complicated; in this instance, crystal structures show that TDG recognizes G:X mismatch DNA containing DNA and G:5caC containing DNA from the minor groove of DNA, which suggested that TDG might recognize 5mC oxidized product 5caC like mismatch DNA. In mutation studies, a N157D mutation results in a more 5caC specific glycosylase, and a N191A mutation inhibits 5caC activity while that when X=5fC or T remains. Here I revisit the recent MBD4 glycos ylase domain co-crystal structures with DNA, as well as TDG glycosylase domain co-crystal structures with DNA in conjunction with its mutation studies.