Differential Base Stacking Interactions Induced by Trimethylene Interstrand DNA Cross-Links in the 5′-CpG-3′ and 5′-GpC-3′ Sequence Contexts

Abstract

Synthetically derived trimethylene interstrand DNA cross-links have been used as surrogates for the native cross-links that arise from the 1,N2-deoxyguanosine adducts derived from α,β-unsaturated aldehydes. The native enal-mediated cross-linking occurs in the 5′-CpG-3′ sequence context but not in the 5′-GpC-3′ sequence context. The ability of the native enal-derived 1,N2-dG adducts to induce interstrand DNA cross-links in the 5′-CpG-3′ sequence as opposed to the 5′-GpC-3′ sequence is attributed to the destabilization of the DNA duplex in the latter sequence context. Here, we report higher accuracy solution structures of the synthetically derived trimethylene cross-links, which are refined from NMR data with the AMBER force field. When the synthetic trimethylene cross-links are placed into either the 5′-CpG-3′ or the 5′-GpC-3′ sequence contexts, the DNA duplex maintains B-DNA geometry with structural perturbations confined to the cross-linked base pairs. Watson−Crick hydrogen bonding is conserved throughout the duplexes. Although different from canonical B-DNA stacking, the cross-linked and the neighbor base pairs stack in the 5′-CpG-3′ sequence. In contrast, the stacking at the cross-linked base pairs in the 5′-GpC-3′ sequence is greatly perturbed. The π-stacking interactions between the cross-linked and the neighbor base pairs are reduced. This is consistent with remarkable chemical shift perturbations of the C5 H5 and H6 nucleobase protons that shifted downfield by 0.4−0.5 ppm. In contrast, these chemical shift perturbations in the 5′-CpG-3′ sequence are not remarkable, consistent with the stacked structure. The differential stacking of the base pairs at the cross-linking region probably explains the difference in stabilities of the trimethylene cross-links in the 5′-CpG-3′ and 5′-GpC-3′ sequence contexts and might, in turn, account for the sequence selectivity of the interstrand cross-link formation induced by the native enal-derived 1,N2-dG adducts.