Stavros KM, Hawkins EK, Rizzo CJ, Stone MP. Base-Displaced Intercalated Conformation of the 2-Amino-3-methylimidazo[4,5-f]quinoline N(2)-dG DNA Adduct Positioned at the Nonreiterated G(1) in the NarI Restriction Site.
Chem Res Toxicol 2015;
28:1455-68. [PMID:
26083477 PMCID:
PMC4511292 DOI:
10.1021/acs.chemrestox.5b00140]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
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The
conformation of an N2-dG adduct
arising from the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a potent food mutagen, was determined
in 5′-d(C1T2C3X4G5C6G7C8C9A10T11C12)-3′:5′-d(G13A14T15G16G17C18G19C20C21G22A23G24)-3′; X = N2-dG-IQ, in which the modified nucleotide X4 corresponds to G1 in the 5′-d(G1G2CG3CC)-3′ NarI restriction endonuclease site. Circular dichroism (CD) revealed
blue shifts relative to the unmodified duplex, consistent with adduct-induced
twisting, and a hypochromic effect for the IQ absorbance in the near
UV region. NMR revealed that the N2-dG-IQ
adduct adopted a base-displaced intercalated conformation in which
the modified guanine remained in the anti conformation
about the glycosidic bond, the IQ moiety intercalated into the duplex,
and the complementary base C21 was displaced into the major
groove. The processing of the N2-dG-IQ
lesion by hpol η is sequence-dependent; when placed at the reiterated
G3 position, but not at the G1 position, this
lesion exhibits a propensity for frameshift replication [Choi, J.
Y., et al. (2006) J. Biol. Chem., 281, 25297–25306]. The structure of the N2-dG-IQ adduct at the nonreiterated G1 position
was compared to that of the same adduct placed at the G3 position [Stavros, K. M., et al. (2014) Nucleic Acids Res., 42, 3450–3463]. CD indicted minimal spectral
differences between the G1 vs G3N2-dG-IQ adducts. NMR indicated that the N2-dG-IQ adduct exhibited similar base-displaced intercalated
conformations at both the G1 and G3 positions.
This result differed as compared to the corresponding C8-dG-IQ adducts
placed at the same positions. The C8-dG-IQ adduct adopted a minor
groove conformation when placed at position G1 but a base-displaced
intercalated conformation when placed at position G3 in
the NarI sequence. The present studies suggest that
differences in lesion bypass by hpol η may be mediated by differences
in the 3′-flanking sequences, perhaps modulating the ability
to accommodate transient strand slippage intermediates.
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