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PostInsertion complex of Human DNA Polymerase Eta bypassing an O6-Methyl-2'-deoxyguanosine : dC sitePostInsertion complex of Human DNA Polymerase Eta bypassing an O6-Methyl-2'-deoxyguanosine : dC site
Structural highlights
DiseasePOLH_HUMAN Defects in POLH are the cause of xeroderma pigmentosum variant type (XPV) [MIM:278750; also designated as XP-V. Xeroderma pigmentosum (XP) is an autosomal recessive disease due to deficient nucleotide excision repair. It is characterized by hypersensitivity of the skin to sunlight, followed by high incidence of skin cancer and frequent neurologic abnormalities. XPV shows normal nucleotide excision repair, but an exaggerated delay in recovery of replicative DNA synthesis. Most XPV patients do not develop clinical symptoms and skin neoplasias until a later age. Clinical manifestations are limited to photo-induced deterioration of the skin and eyes.[1] [2] [3] [4] [5] FunctionPOLH_HUMAN 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. Plays an important role in the repair of UV-induced pyrimidine dimers. Depending on the context, it inserts the correct base, but causes frequent base transitions and transversions. May play a role in hypermutation at immunoglobulin genes. Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but does not have lyase activity. Targets POLI to replication foci.[6] [7] [8] [9] [10] Publication Abstract from PubMedO6-Methyl-2(prime)-deoxyguanosine (O6-MeG) is a ubiquitous DNA lesion, formed not only by xenobiotic carcinogens but also by the endogenous methylating agent S-adenosylmethionine. It can introduce mutations during DNA replication, with different DNA polymerases displaying different ratios of correct or incorrect incoporation opposite this nucleoside. Of the "translesion" Y-family human DNA polymerases (hpols), hpol eta is most efficient in incorporating equal numbers of correct and incorrect C and T bases. However, the mechanistic basis for this specific yet indescriminate activity is not known. To explore this question, we report biochemical and structural analysis of the catalytic core of hpol eta. Activity assays showed the truncated form displayed similar misincorporation properties as the full-length enzyme, incorporating C and T equally and extending from both. X-ray crystal structures of both dC and dT paired with O6-MeG were solved, in both insertion and extension modes. The structures revealed a Watson-Crick-like pairing between O6-MeG and dTMPNPP (approximating dT) at both the insertion and extension stages with formation of two H-bonds. Conversely, both the structures with O6-MeG opposite dCTP and dC display sheared configuration of base pairs, but to different degrees, with formation of two bifurcated H-bonds and two single H-bonds in the structures trapped in the insertion and extension states, respectively. The structural data are consistent with the observed tendency of hpol eta to insert both dC and dT opposite the O6-MeG lesion with similar efficiencies. Comparison of the hpol eta active site configurations with either O6-MeG:dC or O6-MeG:dT bound compared to the corresponding situations in structures of complexes of Sulfolobus solfataricus Dpo4, a bypass pol that favors C relative to T by a factor of ~4, helps rationalize the more error-prone synthesis opposite the lesion by hpol eta. Mechanisms of Insertion of dCTP and dTTP Opposite the DNA lesion O6-Methyl-2'-deoxyguanosine by Human DNA Polymerase eta.,Patra A, Zhang Q, Guengerich FP, Egli M J Biol Chem. 2016 Sep 30. pii: jbc.M116.755462. PMID:27694439[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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