Title
Conformational Preference and Fluorescence Response of a C-Linked C8-Biphenyl-Guanine Lesion in the NarI Mutational Hotspot: Evidence for Enhanced Syn Adduct Formation
Author
Florence D. Berger, Shana J. Sturla, Ryan W. Kung, Tony Montina, Stacey D. Wetmore, Richard A. Manderville
Year
2018
Journal
Chemical Research in Toxicology
Abstract
Aromatic chemical carcinogens can undergo enzymatic transformations to produce a range of electrophilic species that attach covalently to the C8-site of 2′-deoxyguanosine (dG) to afford C8-dG adducts. The most studied C8-dG adducts are formed from arylamines and contain a N-linkage separating the dG from the C8-aryl moiety. Other carcinogenic species result in direct aryl ring attachment to the dG moiety, resulting in C-linked adducts. The resulting C-linked adducts have reduced conformational flexibility compared to the corresponding N-linked C8-dG adducts, which can alter their orientation in the DNA duplex. Described herein are structural studies of a fluorescent C-linked 4-fluorobiphenyl-dG (FBP-dG) that has been incorporated into the reiterated G3-postion of the 12-mer NarI sequence and those containing other 5′-flanking nucleobases. FBP-dG displays a strong preference for adopting a syn conformation in the fully paired NarI duplex to produce an intercalated structure that exhibits stacking interactions between the C-linked biphenyl and the flanking bases. FBP-dG is also shown to significantly stabilize the slippage mutagenic intermediate (SMI) duplex containing the lesion and 5′-flanking base within a 2-base bulge. FBP-dG exhibits fluorescence sensitivity to SMI duplex formation that can readily distinguish it from the fully paired duplex. Molecular dynamics simulations and optical spectroscopy for the NarI oligonucleotides containing the C-linked FBP-dG predict increased rigidity of the biphenyl in the syn conformation. The greater propensity to generate the promutagenic syn conformation for the C-linked FBP-dG adduct compared to the N-linked 4-aminobiphenyl-dG adduct (ABP-dG) suggests greater mutagenicity for the C-linked analogue. These results highlight the effect of the adduct linkage type on the conformational properties of adducted DNA. The turn-on emission response of FBP-dG in the SMI duplex may be a powerful tool for monitoring SMI formation in the NarI sequence upon synthesis with DNA polymerases.
Instrument
J-815
Keywords
Circular dichroism, DNA structure, Biochemistry, Toxicology