3q8r
From Proteopedia
Human DNA polymerase iota incorporating dGTP opposite 8-oxo-guanine
Structural highlights
Function[POLI_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 PubMedThe 8-oxo-guanine (8-oxo-G) lesion is the most abundant and mutagenic oxidative DNA damage existing in the genome. Due to its dual coding nature, 8-oxo-G causes most DNA polymerases to misincorporate adenine. Human Y-family DNA polymerase iota (poliota) preferentially incorporates the correct cytosine nucleotide opposite 8-oxo-G. This unique specificity may contribute to poliota's biological role in cellular protection against oxidative stress. However, the structural basis of this preferential cytosine incorporation is currently unknown. Here we present four crystal structures of poliota in complex with DNA containing an 8-oxo-G lesion, paired with correct dCTP or incorrect dATP, dGTP, and dTTP nucleotides. An exceptionally narrow poliota active site restricts the purine bases in a syn conformation, which prevents the dual coding properties of 8-oxo-G by inhibiting syn/anti conformational equilibrium. More importantly, the 8-oxo-G base in a syn conformation is not mutagenic in poliota because its Hoogsteen edge does not form a stable base pair with dATP in the narrow active site. Instead, the syn 8-oxo-G template base forms the most stable replicating base pair with correct dCTP due to its small pyrimidine base size and enhanced hydrogen bonding with the Hoogsteen edge of 8-oxo-G. In combination with site directed mutagenesis, we show that Gln59 in the finger domain specifically interacts with the additional O(8) atom of the lesion base, which influences nucleotide selection, enzymatic efficiency, and replication stalling at the lesion site. Our work provides the structural mechanism of high-fidelity 8-oxo-G replication by a human DNA polymerase. Unique active site promotes error-free replication opposite an 8-oxo-guanine lesion by human DNA polymerase iota.,Kirouac KN, Ling H Proc Natl Acad Sci U S A. 2011 Feb 22;108(8):3210-5. Epub 2011 Feb 7. PMID:21300901[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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