title: DNA binding, nucleotide flipping, and the helix-turn-helix motif in base repair by O6-alkylguanine-DNA alkyltransferase and its implications for cancer chemotherapy.
abstract: O(6)-Alkylguanine-DNA alkyltransferase (AGT) is a crucial target both for the prevention of cancer and for chemotherapy, since it repairs mutagenic lesions in DNA, and it limits the effectiveness of alkylating chemotherapies. AGT catalyzes the unique, single-step, direct damage reversal repair of O(6)-alkylguanines by selectively transferring the O(6)-alkyl adduct to an internal cysteine residue. Recent crystal structures of human AGT alone and in complex with substrate DNA reveal a two-domain alpha/beta fold and a bound zinc ion. AGT uses its helix-turn-helix motif to bind substrate DNA via the minor groove. The alkylated guanine is then flipped out from the base stack into the AGT active site for repair by covalent transfer of the alkyl adduct to Cys145. An asparagine hinge (Asn137) couples the helix-turn-helix DNA binding and active site motifs. An arginine finger (Arg128) stabilizes the extrahelical DNA conformation. With this newly improved structural understanding of AGT and its interactions with biologically relevant substrates, we can now begin to unravel the role it plays in preserving genetic integrity and discover how it promotes resistance to anticancer therapies.
authors.affiliation: The Scripps Research Institute, The Skaggs Institute for Chemical Biology and Department of Molecular Biology, 10550 North Torrey Pines Road, MB4, La Jolla, CA 92037, USA.
authors.forename: Julie L
authors.initials: JL
authors.lastname: Tubbs
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Pegg
authors.forename: John A
authors.initials: JA
authors.lastname: Tainer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D019077:Helix-Turn-Helix Motifs; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism; D009711:Nucleotides / Q000737:chemistry; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D025521:Tumor Suppressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D009711:Nucleotides; D025521:Tumor Suppressor Proteins; D004247:DNA; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D019853:O(6)-Methylguanine-DNA Methyltransferase; D045643:DNA Repair Enzymes