Book of Abstracts: Albany 2007
June 19-23 2007
Structural Characterization of Clustered DNA Damage: Bistranded Oxidized Bases and Abasic Sites
Ionizing radiation (IR) damages cellular DNA mainly by oxidative mechanisms. Since a single energy deposition event generates several free radicals, IR normally produces both isolated lesions and clustered damage sites, operationally defined as two or more lesions within a helical turn. Clustered lesions can occur in one or both strands of the duplex and, in both cases, they affect the efficiency of DNA repair. It has been shown that the repair rate of bistranded clusters is generally reduced and depends on the distance separating the lesions and their relative orientation. The structural basis of these effects remains to be determined. In order to identify structural features that modulate the recognition of cluster lesions by repair enzymes we have prepared two pairs of DNA duplexes containing a bistranded clusters, in the +1 or -1 orientation and determined their structure in solution using high-resolution NMR spectroscopy. The first pair of damaged duplexes contains bistranded dihydrothymine (DHT)/ abasic site (AP) lesions, while the second has a 7,8-dihydro-8-oxoguanine (8-oxoG)/AP cluster.
Our NMR data indicate that all four clusters are readily accommodated in the right-handed duplexes, where they cause only small perturbations of the local DNA structure. The 8-oxo-dG and DHT residues form canonical Watson-Crick alignments and the AP residues remain inside the helix, where they adopt a C2?-endo conformation.