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From Proteopedia
Structural Basis for Proficient Incorporation of dTTP Opposite O6-Methylguanine by Human DNA Polymerase Iota
Structural highlights
FunctionPOLI_HUMAN Error-prone DNA polymerase specifically involved in DNA repair. Plays an important role in translesion synthesis, where the normal high-fidelity DNA polymerases cannot proceed and DNA synthesis stalls. Favors Hoogsteen base-pairing in the active site. Inserts the correct base with high-fidelity opposite an adenosine template. Exhibits low fidelity and efficiency opposite a thymidine template, where it will preferentially insert guanosine. May play a role in hypermutation of immunogobulin genes. Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but may not have lyase activity.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedO(6)-methylguanine (O(6)-methylG) is highly mutagenic and is commonly found in DNA exposed to methylating agents, even physiological ones (e.g. S-adenosylmethionine). The efficiency of a truncated, catalytic DNA polymerase iota core enzyme was determined for nucleoside triphosphate incorporation opposite O(6)-methylG, using steady-state kinetic analyses. The results presented here corroborate previous work from this laboratory using full-length pol iota, which showed that dTTP incorporation occurs with high efficiency opposite O(6)-methylG. Misincorporation of dTTP opposite O(6)-methylG occurred with approximately 6-fold higher efficiency than incorporation of dCTP. Crystal structures of the truncated form of pol iota with O(6)-methylG as the template base and incoming dCTP or dTTP were solved and showed that O(6)-methylG is rotated into the syn conformation in the pol iota active site and that dTTP misincorporation by pol iota is the result of Hoogsteen base pairing with the adduct. Both dCTP and dTTP base paired with the Hoogsteen edge of O(6)-methylG. A single, short hydrogen bond formed between the N3 atom of dTTP and the N7 atom of O(6)-methylG. Protonation of the N3 atom of dCTP and bifurcation of the N3 hydrogen between the N7 and O(6) atoms of O(6)-methylG allow base pairing of the lesion with dCTP. We conclude that differences in the Hoogsteen hydrogen bonding between nucleotides is the main factor in the preferential selectivity of dTTP opposite O(6)-methylG by human pol iota, in contrast to the mispairing modes observed previously for O(6)-methylG in the structures of the model DNA polymerases Sulfolobus solfataricus Dpo4 and Bacillus stearothermophilus DNA polymerase I. Structural basis for proficient incorporation of dTTP opposite O6-methylguanine by human DNA polymerase iota.,Pence MG, Choi JY, Egli M, Guengerich FP J Biol Chem. 2010 Dec 24;285(52):40666-72. Epub 2010 Oct 20. PMID:20961860[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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