Application Of Nmr Spectroscopy In Chemical And Biochemi

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Benzo[a]pyrene (BaP) is believed to initiate cell transformation through covalent binding with the exocyclic N-2 of deoxyguanosine (dG) or N-6 of deoxyadenosine (dA) in DNA. These interactions are mediated by highly reactive bay-region diol epoxides (DE) metabolically derived from BaP. A total of eight isomeric BaP DE adducts are possible at a given base. Differences in mutagenic activities have been reported among various BaP DE adducts. Since cell mutation is believed to commence upon binding of DEs to DNA, the mutagenic variation are most likely arising from conformational differences rooted in these BaP DE adducts. We have been using 2D NMR to determine solution structures of DNA dA adducts formed from specific DEs. Our current NMR study constitutes the first successful structure determination of a fully complementary DNA duplex containing a (10S)-dA adduct of a BaP DE, namely, the trans opened adduct derived from (+)-(7S,8R,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-BaP DE1]. All DE-dA adducts examined to date show hydrocarbon intercalation into the DNA duplex. The hydrocarbon portion of adducts with R configuration at the site of attachment to the adenine base inserts toward the 5'-end of the modified dA, whereas the hydrocarbon in adducts with S configuration inserts towrd the 3'-end. This is in contrast to DE-dG adducts. The NMR studies have revealed that the hydrocarbon oriented in the minor groove for the trans opened dG adducts of BaP DEs, and the corresponding cis opened dG adducts are intercalated with displacement of the modified guanine and its complementary cytosine base. Our current NMR studies of dA adducts derived from BaP DEs have shown the presence of syn-anti conformational interconversion around the glycosidic bonds of these adducts. Interconversion of conformational isomers of oligonucleotides containing DE adducts has been suggested as possibly contributing to multiple types of mutations induced by a single adduct