5ewf
From Proteopedia
Ternary complex of human DNA polymerase eta inserting rCTP opposite an 8-Oxodeoxyguanosine Lesion
Structural highlights
Disease[POLH_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] Function[POLH_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 PubMedRibonucleotides and 2'-deoxyribonucleotides are the basic units for RNA and DNA, respectively, and the only difference is the extra 2'-OH group on the RNA sugar. Cellular rNTP concentrations are much higher than those of dNTP. When copying DNA, DNA polymerases not only select the base of the incoming dNTP to conform to Watson-Crick pairing with the template base but also distinguish the sugar moiety. Some DNA polymerases use a steric gate residue to prevent rNTP incorporation by creating a clash with the 2'-OH group. Y-family human DNA polymerase eta (hpol eta) is of interest owing to its spacious active site (especially in the major groove) and tolerance of DNA lesions. Here, we show that hpol eta maintains base selectivity when incorporating rNTPs opposite undamaged DNA and the DNA lesions 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) and cyclobutane pyrimidine dimer (CPD) but with rates that are 103-fold lower than for inserting the corresponding dNTPs. X-ray crystal structures show that hpol eta scaffolds the incoming rNTP to pair with the template base (dG) or 8-oxodG with a significant propeller twist. As a result, the 2'-OH group avoids a clash with the steric gate, Phe-18, but the distance between primer end and Palpha of the incoming rNTP increases by 1 A, elevating the energy barrier and slowing polymerization compared with dNTP. In addition, Tyr-92 was identified as a second line of defense to maintain the position of Phe-18. This is the first crystal structure of a DNA polymerase with an incoming rNTP opposite a DNA lesion. Mechanism of Ribonucleotide Incorporation by Human DNA Polymerase eta.,Su Y, Egli M, Guengerich FP J Biol Chem. 2016 Jan 6. pii: jbc.M115.706226. PMID:26740629[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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