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Structural Refinement of the 8,9-Dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1 Adduct in a 5‘-CpAFBG-3‘ Sequence

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journal contribution
posted on 24.04.2002, 00:00 by Indrajit Giri, Mark D. Jenkins, Nathalie C. Schnetz-Boutaud, Michael P. Stone
The structure of the cationic 8,9-dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1 adduct embedded in a 5‘-CpG-3‘ sequence context and paired with deoxycytosine in the oligodeoxynucleotide d(ACATCAFBGATCT)·d(AGATCGATGT) was refined using molecular dynamics calculations restrained by NOE data and dihedral angle restraints obtained from NMR data. The aflatoxin moiety intercalated above the 5‘ face of the modified guanine. It stacked between C5·G16 and AFBG6·C15. The AFB1 H5, OCH3, and methylene protons faced into the minor groove, with the methylene protons oriented between the C15 and G16 nucleobases. The aflatoxin B1 H6a, H8, H9, and H9a protons faced the major groove, with H6a and H9a pointing toward the 5‘ direction from the lesion site. The refined structure was compared to the structure of the aflatoxin B1 adduct embedded in a 5‘-ATGCAT-3‘ sequence in the oligodeoxynucleotide d(TATAFBGCATA)2 [Jones, W. R., Johnston, D. S., and Stone, M. P. (1998) Chem. Res. Toxicol. 11, 873−881]. The structure of the intercalated aflatoxin B1 lesion in the ATCAFBGAT sequence is similar to its structure in the d(ATAFBGCAT) sequence. This is consistent with a mechanism in which the precovalent intercalation of aflatoxin-8,9-exo-epoxide on the 5‘ face of guanine places the epoxide in close proximity and in the proper orientation to the N7 position of guanine, thus facilitating an SN2 reaction. The data provides additional insight into the nature of the disruption of the B-DNA duplex induced by aflatoxin B1 intercalation. Overall, the results suggest that sequence contributes a minor role in modulating the structure of the cationic guanine N7 AFB1 lesion in duplex DNA. On the other hand, structural differences are observed when the correctly paired structure is compared to the structure of the cationic AFB1 adduct mispaired with dA [Giri, I., Johnston, D. S., and Stone, M. P. (2002) Biochemistry 41, 5462−5472].