title: Mismatch repair in methylated DNA. Structure and activity of the mismatch-specific thymine glycosylase domain of methyl-CpG-binding protein MBD4.
abstract: MBD4 is a member of the methyl-CpG-binding protein family. It contains two DNA binding domains, an amino-proximal methyl-CpG binding domain (MBD) and a C-terminal mismatch-specific glycosylase domain. Limited in vitro proteolysis of mouse MBD4 yields two stable fragments: a 139-residue fragment including the MBD, and the other 155-residue fragment including the glycosylase domain. Here we show that the latter fragment is active as a glycosylase on a DNA duplex containing a G:T mismatch within a CpG sequence context. The crystal structure confirmed the C-terminal domain is a member of the helix-hairpin-helix DNA glycosylase superfamily. The MBD4 active site is situated in a cleft that likely orients and binds DNA. Modeling studies suggest the mismatched target nucleotide will be flipped out into the active site where candidate residues for catalysis and substrate specificity are present.
authors.affiliation: Department of Biochemistry, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: Peiying
authors.initials: P
authors.lastname: Wu
authors.forename: Chen
authors.initials: C
authors.lastname: Qiu
authors.forename: Anjum
authors.initials: A
authors.lastname: Sohail
authors.forename: Xing
authors.initials: X
authors.lastname: Zhang
authors.forename: Ashok S
authors.initials: AS
authors.lastname: Bhagwat
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Cheng
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020137:Base Pair Mismatch; D019175:DNA Methylation; D004260:DNA Repair; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C492249:Mbd4 protein, mouse