2hw3
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T:O6-methyl-guanine pair in the polymerase postinsertion site (-1 basepair position)
OverviewOverview
Methylating agents are widespread environmental carcinogens that generate, a broad spectrum of DNA damage. Methylation at the guanine O(6) position, confers the greatest mutagenic and carcinogenic potential. DNA polymerases, insert cytosine and thymine with similar efficiency opposite, O(6)-methyl-guanine (O6MeG). We combined pre-steady-state kinetic analysis, and a series of nine x-ray crystal structures to contrast the reaction, pathways of accurate and mutagenic replication of O6MeG in a high-fidelity, DNA polymerase from Bacillus stearothermophilus. Polymerases achieve, substrate specificity by selecting for nucleotides with shape and, hydrogen-bonding patterns that complement a canonical DNA template. Our, structures reveal that both thymine and cytosine O6MeG base pairs evade, proofreading by mimicking the essential molecular features of canonical, substrates. The steric mimicry depends on stabilization of a rare cytosine, tautomer in C.O6MeG-polymerase complexes. An unusual electrostatic, interaction between O-methyl protons and a thymine carbonyl oxygen helps, stabilize T.O6MeG pairs bound to DNA polymerase. Because DNA methylators, constitute an important class of chemotherapeutic agents, the molecular, mechanisms of replication of these DNA lesions are important for our, understanding of both the genesis and treatment of cancer.
About this StructureAbout this Structure
2HW3 is a Single protein structure of sequence from Geobacillus stearothermophilus with , and as ligands. Active as DNA-directed DNA polymerase, with EC number 2.7.7.7 Full crystallographic information is available from OCA.
ReferenceReference
The structural basis for the mutagenicity of O(6)-methyl-guanine lesions., Warren JJ, Forsberg LJ, Beese LS, Proc Natl Acad Sci U S A. 2006 Dec 26;103(52):19701-6. Epub 2006 Dec 18. PMID:17179038
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