42583-46-0Relevant articles and documents
Structural perturbations induced by the α-anomer of the aflatoxin B1 formamidopyrimidine adduct in duplex and single-strand DNA
Brown, Kyle L.,Voehler, Markus W.,Magee, Shane M.,Harris, Constance M.,Harris, Thomas M.,Stone, Michael P.
, p. 16096 - 16107 (2009)
The guanine N7 adduct of aflatoxin B1 exo-8,9-epoxide hydrolyzes to form the formamidopyrimidine (AFB-FAPY) adduct, which interconverts between R and β anomers. The β anomer is highly mutagenic in Escherichia coli, producing G → T transversions; it thermally stabilizes the DNA duplex. The AFB-α-FAPY adduct blocks replication; it destabilizes the DNA duplex. Herein, the structure of the AFB-α-FAPY adduct has been elucidated in 5′-d(C1T2A3T4X 5A6T7T8C9A 10)-3′ ?5′-d(T11G12A 13A14T15C16A17T 18A19G20)-3′ (X = AFB-α-FAPY) using molecular dynamics calculations restrained by NMR-derived distances and torsion angles. The AFB moiety intercalates on the 5′ face of the pyrimidine moiety at the damaged nucleotide between base pairs T4 ?A 17 and X5 ?C16, placing the FAPY C5-N 5 bond in the Ra axial conformation. Large perturbations of the ε and ζ backbone torsion angles are observed, and the base stacking register of the duplex is perturbed. The deoxyribose orientation shifts to become parallel to the FAPY base and displaced toward the minor groove. Intrastrand stacking between the AFB moiety and the 5′ neighbor thymine remains, but strong interstrand stacking is not observed. A hydrogen bond between the formyl group and the exocyclic amine of the 3′-neighbor adenine stabilizes the E conformation of the formamide moiety. NMR studies reveal a similar 5′-intercalation of the AFB moiety for the AFB-β-FAPY adduct in the tetramer 5′-d(C1T 2X3A4)-3′, involving the Ra axial conformation of the FAPY C5-N5 bond and the E conformation of the formamide moiety. Since in duplex DNA the AFB moiety of the AFB-β-FAPY adduct also intercalates on the 5′ side of the pyrimidine moiety at the damaged nucleotide, we conclude that favorable 5′-stacking leads to the Ra conformational preference about the C5-N5 bond; the same conformational preference about this bond is also observed at the nucleoside and base levels. The structural distortions and the less favorable stacking interactions induced by the AFB-α-FAPY adduct explain its lower stability as compared to the AFB-β-FAPY adduct in duplex DNA. In this DNA sequence, hydrogen bonding between the formyl oxygen and the exocyclic amine of the 3′-neighboring adenine stabilizing the E configuration of the formamide moiety is also observed for the AFB-β-FAPY adduct, and suggests that the identity of the 3′-neighbor nucleotide modulates the stability and biological processing of AFB adducts.
Preparation of the 8,9-epoxide of the mycotoxin aflatoxin B1: The ultimate carcinogenic species
Baertschi,Raney,Stone,Harris
, p. 7929 - 7931 (1988)
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Interaction of aflatoxin B1 with cytochrome P450 2A5 and its mutants: correlation with metabolic activation and toxicity.
Pelkonen,Lang,Negishi,Wild,Juvonen
, p. 85 - 90 (2007/10/03)
Among members of the mouse cytochrome P450 2A family, P450 2A5 is the best catalyst of aflatoxin B1 (AFB1) oxidation to its 8,9-epoxide (Pelkonen, P., Lang, M., Wild, C. P., Negishi, M., and Juvonen, R. O. (1994) Eur. J. Pharmacol., Environ. Toxicol. Pharmacol. Sect. 292, 67-73). Here we studied the role of amino acid residues 209 and 365 of the P450 2A5 in the metabolism and toxicity of AFB1 using recombinant yeasts. The two sites have previously been shown to be essential in the interaction of coumarin and steroids with the P450 2A5. Reducing the size of the amino acid at position 209 or introducing a negatively charged residue at this site increased the 8,9-epoxidation of AFB1 compared to the wild type. In addition, replacing the hydrophobic amino acid at the 365 position with a positively charged lysine residue strongly decreased the metabolism of AFB1. These mutations changed the KM values generally less than the Vmax values. The changes in AFB1 metabolism contrast with the changes in coumarin 7-hydroxylation caused by these amino acid substitutions, since reducing the size of the 209 residue strongly reduced coumarin metabolism and increased the K(M) values. On the other hand, the results with AFB1 are similar to those obtained with steroid hydroxylation. This suggests that the size of the substrate is important when interacting with the residue 209 of the protein. The catalytic parameters of AFB1 correlated generally with its toxicity to the recombinant yeasts expressing the activating enzyme and with the binding of AFB1 to yeast DNA. Furthermore high affinity substrates and inhibitors (e.g., methoxsalen, metyrapone, coumarin 311, 7-methylcoumarin, coumarin, and pilocarpine) of P450 2A5 could efficiently block the toxicity of AFB1. It is suggested that the recombinant yeasts expressing engineered P450 enzymes are a useful model to understand the substrate protein interactions, to study the relationship of metabolic parameters to toxicity, and to test potential inhibitors of metabolism based toxicity.
