STRUCTURE OF A DUPLEX OLIGODEOXYNUCLEOTIDE CONTAINING PROPANODEOXYGUANOSINE OPPOSITE A 2-BASE DELETION IN THE (CPG)(3) FRAME-SHIFT HOTSPOT OF SALMONELLA-TYPHIMURIUM HISD3052 DETERMINED BY H-1-NMR AND RESTRAINED MOLECULAR-DYNAMICS

Structural refinement from solution H-1 NMR data was performed on the 5'-d[ATCGC(PdG)CGGCATG]-3'.5'-d[CATGCCGCCAT]-3' duplex, in which the adducted oligodeoxynucleotide containing the exocyclic lesion 1,N-2-propano-2'-deoxyguanosine (PdG) was annealed with the complementary strand which contained a CpG deletion. The resulting duplex required PdG and one adjacent cytosine to be unpaired. A total of 352 distances were utilized to restrain molecular dynamics calculations, of which 264 were NOE-derived. These distances were calculated using complete relaxation matrix methods from hybrid matrices, which were comprised of the experimentally determined distances and additional distances derived from either A-form or B-form DNA. A simulated annealing protocol combined with the distance restraints was able to refine a single structure with an average rms deviation of <1.35 Angstrom. The accuracy of the refined structure was assessed using full relaxation matrix calculations, which gave good agreement with measured NOE intensities. PdG was found to be stacked into the helix below base pair C-3.G(18) whereas C-5 was found to be unpaired and extruded toward the major groove and parallel to base pair G(6).C-17. This created a localized bend in the DNA helix of approximately 20-35 degrees at the junction between PdG and C-5. The bending corroborated previous assays performed on this modified sequence [Moe, J. G., Reddy, G. R., Marnett, L. J., & Stone, M. P. (1994) Chem. Res. Toxicol. 7, 319-328].