title: Crystal structure of a thwarted mismatch glycosylase DNA repair complex.
abstract: The bacterial mismatch-specific uracil-DNA glycosylase (MUG) and eukaryotic thymine-DNA glycosylase (TDG) enzymes form a homologous family of DNA glycosylases that initiate base-excision repair of G:U/T mismatches. Despite low sequence homology, the MUG/TDG enzymes are structurally related to the uracil-DNA glycosylase enzymes, but have a very different mechanism for substrate recognition. We have now determined the crystal structure of the Escherichia coli MUG enzyme complexed with an oligonucleotide containing a non-hydrolysable deoxyuridine analogue mismatched with guanine, providing the first structure of an intact substrate-nucleotide productively bound to a hydrolytic DNA glycosylase. The structure of this complex explains the preference for G:U over G:T mispairs, and reveals an essentially non-specific pyrimidine-binding pocket that allows MUG/TDG enzymes to excise the alkylated base, 3, N(4)-ethenocytosine. Together with structures for the free enzyme and for an abasic-DNA product complex, the MUG-substrate analogue complex reveals the conformational changes accompanying the catalytic cycle of substrate binding, base excision and product release.
authors.affiliation: Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT.
authors.forename: T E
authors.initials: TE
authors.lastname: Barrett
authors.forename: O D
authors.initials: OD
authors.lastname: Schärer
authors.forename: R
authors.initials: R
authors.lastname: Savva
authors.forename: T
authors.initials: T
authors.lastname: Brown
authors.forename: J
authors.initials: J
authors.lastname: Jiricny
authors.forename: G L
authors.initials: GL
authors.lastname: Verdine
authors.forename: L H
authors.initials: LH
authors.lastname: Pearl
mesh_terms: D020137:Base Pair Mismatch; D002384:Catalysis; D018360:Crystallography, X-Ray; D003596:Cytosine / Q000031:analogs & derivatives / Q000737:chemistry; D004260:DNA Repair; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D009699:N-Glycosyl Hydrolases / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D013941:Thymine / Q000737:chemistry; D044502:Thymine DNA Glycosylase; D014498:Uracil / Q000737:chemistry
chemical_list: C018289:3,N(4)-ethenocytosine; D014498:Uracil; D003596:Cytosine; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); D009699:N-Glycosyl Hydrolases; D044502:Thymine DNA Glycosylase; C113921:mismatch-specific thymine uracil-DNA glycosylase; D013941:Thymine