Structures and energetics of base flipping of the thymine dimer depend on DNA sequence.
The cis,syn-cyclobutane pyrimidine dimer (CPD) is a photoinduced DNA lesion leading to a significant distortion of the DNA structure. Its repair by DNA photolyase requires a flip of the damaged base into an extrahelical position. This base flip is expected to be sequence-dependent, but the structures and energetics as a function of the bases 3' and 5' to the CPD lesion are unknown. Eight-nanosecond MD simulations of four different hexadecamer duplexes with the CPD were performed for the flipped-in and flipped-out structures. Analysis of these results indicates clear sequence-dependent differences. Significant disruptions of the base pairs to the 3' side of the CPD are observed for the flipped-out structures with adjacent A-T pairs, whereas those with G-C pairs adjacent show no such distortions. The conformational spaces occupied by these two duplexes are significantly different. The structural differences correlate well with the free energy differences for base flipping calculated using the previously established 2D potential of mean force (PMF) method. The energy differences for base flipping in duplexes containing A, T, G, and C pairs adjacent to the CPD were found to be 6.25-6.5, 5.25-5.5, 7.25-7.5, and 6.5-6.75 kcal/mol, respectively. These energy differences of up to 2 kcal/mol should be large enough to be detected experimentally using sensitive probes.
O'Neil
Lauren L
LL
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
Wiest
Olaf
O
D001483:Base Sequence; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry; D019281:Dimerization; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011740:Pyrimidine Dimers / Q000737:chemistry* / Q000528:radiation effects; D013816:Thermodynamics; D014466:Ultraviolet Rays
D011740:Pyrimidine Dimers; D004247:DNA; D004255:Deoxyribodipyrimidine Photo-Lyase