Structural and energetic consequences of oxidation of d(ApGpGpGpTpT) telomere repeat unit in complex with TRF1 protein.

The configuration hyperspace of canonical and oxidized 14-mers of B-DNA comprising telomere repeat units d(ApGpGpGpTpT) was sampled over 40 ns via molecular dynamic (MD) simulations. The energetic and structural consequences of TRF1 binding to telomere B-DNA were compared with non-complexed systems. Energetic properties of analyzed pairs, di- and tri-nucleotide steps occurring in central telomere repeat unit were estimated by means of advanced quantum chemistry computations including not only BSSE corrections, electron correlation contributions but also non-negligible many-body terms. These data along with bases pair and base step parameters distributions allow for quantization of consequences of oxidation and/or TRF1 binding to telomere repeat units. Occurrence of 8-oxoguanine in central telomeric triad (CTT) is the source of high stiffness if compared to non-modified oligomer. The origin of this property comes from significantly alteration of intermolecular interactions introduced by 8-oxoguanine. The increased stability observed for base-base interactions are accumulated and characterizes also di- and tri-nucleotides. The observed changes in the intermolecular interactions originate from structural alterations imposed by TRF1 binding to canonical and oxidized telomere B-DNA. First and most direct consequence of TRF1 binding to oxidized telomere repeat unit is alteration of shift-slide correlations if compared to canonical system. This in turn leads to large differences in purine-purine overlapping in oxidized structures. Thus, oxidized telomere B-DNA double strands are sensitive to interactions with protein ligands and numerous structural and energetic changes are imposed on base pairs forming CTT.