DNA binding and nucleotide flipping by the human DNA repair protein AGT

Douglas S. Daniels, Tammy T. Woo, Kieu X. Luu, David M. Noll, Neil D. Clarke, Anthony E. Pegg, John A. Tainer

Research output: Contribution to journalArticlepeer-review

269 Scopus citations


O6-alkylguanine-DNA alkyltransferase (AGT), or O 6-methylguanine-DNA methyltransferase (MGMT), prevents mutations and apoptosis resulting from alkylation damage to guanines. AGT irreversibly transfers the alkyl lesion to an active site cysteine in a stoichiometric, direct damage reversal pathway. AGT expression therefore elicits tumor resistance to alkylating chemotherapies, and AGT inhibitors are in clinical trials. We report here structures of human AGT in complex with double-stranded DNA containing the biological substrate O6-methylguanine or crosslinked to the mechanistic inhibitor N1,O6- ethanoxanthosine. The prototypical DNA major groove-binding helix-turn-helix (HTH) motif mediates unprecedented minor groove DNA binding. This binding architecture has advantages for DNA repair and nucleotide flipping, and provides a paradigm for HTH interactions in sequence-independent DNA-binding proteins like RecQ and BRCA2. Structural and biochemical results further support an unpredicted role for Tyr114 in nucleotide flipping through phosphate rotation and an efficient kinetic mechanism for locating alkylated bases.

Original languageEnglish (US)
Pages (from-to)714-720
Number of pages7
JournalNature Structural and Molecular Biology
Issue number8
StatePublished - Aug 2004

All Science Journal Classification (ASJC) codes

  • Structural Biology
  • Molecular Biology


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