Excision of oxidatively damaged DNA bases by the human α-hOgg1 protein and the polymorphic α-hOgg1(Ser326Cys) protein which is frequently found in human populations

We have investigated the substrate specificity of the major nuclear form of the human Ogg1 protein, referred as α-hOgg1, for excision of damaged bases from DNA exposed to γ-irradiation. Excision products were identified and quantified using gas chromatography/ isotope dilution mass spectrometry (GC/IDMS). The GST‐α-hOgg1 protein used in this study is a fusion of α α α α-hOgg1 to the C-terminus of the GST protein. The results show that GST‐α α α α-hOgg1 protein excises 8hydroxyguanine (8-OH-Gua) and 2,6-diamino-4-hydroxy5-formamidopyrimidine (FapyGua) from DNA exposed to γ γ γ γ-irradiation in a solution saturated with N2 Oo r air. Fourteen other lesions, including oxidised purines and pyrimidines, were not excised from these substrates. Catalytic constants were measured for the excision of 8-OH-Gua and FapyGua from DNA γirradiated under N2O. The kcat/Km values for excision of 8-OH-Gua and FapyGua were 4.47 × 10 ‐5 and 8.97 × × × × 10 ‐5 (min ‐1 nM ‐1 ), respectively. The substrate specificity and the catalytic parameters of the wild-type GST‐α α α αhOgg1 protein were compared to that of a polymorphic form of α-hOgg1 harbouring a Ser→Cys mutation at codon 326. In the Japanese population, 47.6% of individuals possess both alleles coding for the wild-type α