Influence of DNA torsional rigidity on excision of 7,8-dihydro-8-oxo-2′-deoxyguanosine in the presence of opposing abasic sites by human OGG1 protein

The human protein OGG1 (hOGG1) targets the highly mutagenic base 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) and shows a high specificity for the opposite DNA base. Abasic sites can arise in DNA in close opposition to 8-oxodG either during repair of mismatched bases (i.e. 8-oxodG/A mismatches) or, more frequently, as a consequence of ionizing radiation exposure. Bistranded DNA lesions may remain unrepaired and lead to cell death via double-strand break formation. In order to explore the role of damaged-DNA dynamics in recognition/excision by the hOGG1 repair protein, specific oligonucleotides containing an 8-oxodG opposite an abasic site, at different relative distances on the complementary strand, were synthesized. Rotational dynamics were studied by means of fluorescence polarization anisotropy decay experiments and the torsional elastic constant as well as the hydrodynamic radius of the DNA fragments were evaluated. Efficiency of excision of 8-oxodG was tested using purified human glycosylase. A close relation between the twisting flexibility of the DNA fragment and the excision efficiency of the oxidative damage by hOGG1 protein within a cluster was found.