Nucleic Acids Research, 2002, Vol. 30, No. 15 3422-3432
© 2002 Oxford University Press
Relating repair susceptibility of carcinogen-damaged DNA with structural distortion and thermodynamic stability
Department of Chemistry and 1 Department of Biology, New York University, New York, NY 10003, USA and 2 Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
*To whom correspondence should be addressed. Tel: +1 212 998 8231; Fax: +1 212 995 4015; Email: broyde{at}nyu.edu
Correspondence may also be addressed to Nicholas E. Geacintov. Tel: +1 212 998 8407; Fax: +1 212 998 8421; Email: ngl@nyu.edu
A key issue in the nucleotide excision repair (NER) of bulky carcinogenDNA adducts is the ability of the NER machinery to recognize and repair certain adducts while failing to repair others. Unrepaired adducts can survive to cause mutations that initiate the carcinogenic process. Benzo[c]phenanthrene (B[c]Ph), a representative fjord region polycyclic aromatic hydrocarbon, can be metabolically activated to the enantiomeric benzo[c]phenanthrene diol epoxides (B[c]PhDEs), (+)-(1S,2R,3R,4S)-3,4- dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenzo[c]phe nanthrene and the corresponding ()-(1R,2S,3S,4R) isomer. These react predominantly with adenine residues in DNA to produce the stereoisomeric 1R (+)- and 1S ()-trans-anti-B[c]Ph-N6-dA adducts. Duplexes containing the 1R (+) or 1S () B[c]Ph-dA adduct in codon 61 of the human N-ras mutational hotspot sequence CA*A, with B[c]Ph modification at A*, are not repaired by the human NER system. However, the analogous stereoisomeric DNA adducts of the bay region benzo[a]pyrene diol epoxide (B[a]PDE), 10S (+)- and 10R ()-trans-anti-B[a]P-N6-dA, are repaired in the same base sequence. In order to elucidate structural and thermodynamic origins of this phenomenon, we have carried out a 2 ns molecular dynamics simulation for the 1R (+)- and 1S ()-trans-anti-B[c]Ph-N6-dA adducts in an 11mer duplex containing the human N-ras codon 61 sequence, and compared these results with our previous study of the B[a]P-dA adducts in the same sequence. The molecular mechanics Poisson Boltzmann surface area (MM-PBSA) method was applied to calculate the free energies of the pair of stereoisomeric B[c]Ph-dA adducts, and a detailed structural analysis was carried out. The different repair susceptibilities of the B[a]P-dA adducts and the B[c]Ph-dA adducts can be attributed to different degrees of distortion, stemming from combined effects of differences in the quality of WatsonCrick hydrogen bonding, unwinding, stretching and helix backbone perturbations. These differences are due to the different intrinsic topologies of the rigid, planar bay region adducts versus the twisted, sterically hindered fjord region adducts.
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