4rno
From Proteopedia
Crystal structure of human polymerase eta extending an abasic site-dA pair by inserting dCTP opposite template G
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 PubMedThe most common lesion in DNA is an abasic site resulting from glycolytic cleavage of a base. In a number of cellular studies, abasic sites preferentially code for dATP insertion (the "A rule"). In some cases frameshifts are also common. X-ray structures with abasic sites in oligonucleotides have been reported for several microbial and human DNA polymerases (pols), e.g. Dpo4, RB69, KlenTaq, yeast pol iota, human (h) pol iota, and human pol beta. We reported previously that hpol eta is a major pol involved in abasic site bypass (Choi, J.-Y., Lim, S., Kim, E. J., Jo, A., and Guengerich, F. P. (2010 J. Mol. Biol. 404, 34-44). hpol eta inserted all four dNTPs in steady-state and pre-steady-state assays, preferentially inserting A and G. In LC-MS analysis of primer-template pairs, A and G were inserted but little C or T was inserted. Frameshifts were observed when an appropriate pyrimidine was positioned 5' to the abasic site in the template. In x-ray structures of hpol eta with a non-hydrolyzable analog of dATP or dGTP opposite an abasic site, H-bonding was observed between the phosphate 5' to the abasic site and water H-bonded to N1 and N6 of A and N1 and O6 of G nucleoside triphosphate analogs, offering an explanation for what appears to be a "purine rule." A structure was also obtained for an A inserted and bonded in the primer opposite the abasic site, but it did not pair with a 5' T in the template. We conclude that hpol eta, a major copying enzyme with abasic sites, follows a purine rule, which can also lead to frameshifts. The phenomenon can be explained with H-bonds. Structural and Kinetic Analysis of Nucleoside Triphosphate Incorporation Opposite an Abasic Site by Human Translesion DNA Polymerase eta.,Patra A, Zhang Q, Lei L, Su Y, Egli M, Guengerich FP J Biol Chem. 2015 Mar 27;290(13):8028-38. doi: 10.1074/jbc.M115.637561. Epub 2015, Feb 9. PMID:25666608[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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