Impact of benzo[a]pyrene-2′-deoxyguanosine lesions on methylation of DNA by SssI and HhaI DNA methyltransferases

Oksana M. Subach, Vladimir B. Baskunov, Maria V. Darii, Diana V. Maltseva, Dmitrii A. Alexandrov, Olga V. Kirsanova, Alexander Kolbanovskiy, Marina Kolbanovskiy, Francis Johnson, Radha Bonala, Nicholas E. Geacintov, Elizaveta S. Gromova

Research output: Contribution to journalArticlepeer-review


DNA damage caused by the binding of the tumorigen 7R,8S-diol 9S,10R-epoxide (B[a]PDE), a metabolite of bezo[a]pyrene, to guanine in CpG dinucleotide sequences could affect DNA methylation and, thus, represent a potential epigenetic mechanism of chemical carcinogenesis. In this work, we investigated the impact of stereoisomeric (+)- and (-)-trans-anti-B[a]P-N2-dG adducts (B+ and B-) on DNA methylation by prokaryotic DNA methyltransferases M.SssI and M.HhaI. These two methyltransferases recognize CpG and GCGC sequences, respectively, and transfer a methyl group to the C5 atom of cytosine (C). A series of 18-mer unmethylated or hemimethylated oligodeoxynucleotide duplexes containing trans-anti-B[a]P-N2-dG adducts was generated. The B+ or B- residues were introduced either 5′ or 3′ adjacent or opposite to the target 2′-deoxycytidines. The B[a]PDE lesions practically produced no effect on M.SssI binding to DNA but reduced M.HhaI binding by 1-2 orders of magnitude. In most cases, the benzo[a]pyrenyl residues decreased the methylation efficiency of hemimethylated and unmethylated DNA by M.SssI and M.HhaI. An absence of the methylation of hemimethylated duplexes was observed when either the (+)- or the (-)-trans-anti-B[a]P-N2-dG adduct was positioned 5′ to the target dC. The effects observed may be related to the minor groove conformation of the bulky benzo[a]-pyrenyl residue and to a perturbation of the normal contacts of the methyltransferase catalytic loop with the B[a]PDE-modified DNA. Our results indicate that a trans-anti-B[a]P-N2-dG lesion flanking a target dC in the CpG dinucleotide sequence on its 5′-side has a greater adverse impact on methylation than the same lesion when it is 3′ adjacent or opposite to the target dC.

Original languageEnglish (US)
Pages (from-to)6142-6159
Number of pages18
Issue number19
StatePublished - May 16 2006

ASJC Scopus subject areas

  • Biochemistry


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