title: Flanking base effects on the structural conformation of the (+)-trans-anti-benzo[a]pyrene diolepoxide adduct to N2-dG in sequence-defined oligonucleotides.
abstract: Conformations of the trans adduct of (+)-anti-benzo[a]pyrene -7,8-dihydrodiol-9,10-epoxide (BPDE) to N2-guanine, the major stable DNA adduct of the environmental carcinogen benzo[a]pyrene, were studied as a function of flanking bases in single-stranded and in double-stranded oligonucleotides. Three 11mer oligonucleotides d(CTAT-G1G2G3TATC) were synthesized containing the (+)-trans-anti-BPDE adduct at one specific guanine of the GGG sequence (a known mutational hot spot). Polyacrylamide gel electrophoresis of the three single-stranded oligonucleotides showed that the adduct bound to G2 or G3 (5'-flanking base guanine) caused significantly stronger retardation than the same adduct bound to G1 (5'-flanking base thymine). The strength of the carcinogen-base interaction was reflected in the spectroscopic properties of the pyrenyl moiety. Low temperature fluorescence measurements under line-narrowing (FLN) or non-line-narrowing (NLN) conditions showed that in single-stranded form the adduct at G2 or G3 (5'-flanking base guanine) adopts a conformation with strong interaction with the bases. This was also observed for the same adduct at the sequence AGA. In contrast, the (+)-trans-anti-BPDE adduct with a 5'-flanking thymine exists in a primarily helix-external conformation. Similar differences were observed in the double-stranded oligonucleotides: the adducts at G2 and G3 were found to exist in similar conformational equilibria, again with significant carcinogen-base interactions, while the adduct at G1 showed a predominantly external conformation. The nature of the 3'-flanking base appeared to have little influence on the conformational equilibrium of the (+)-trans-anti-BPDE-guanine adduct. The results could provide insight into the mutational specificity and flanking base effects observed for (+)-anti-BPDE.
authors.affiliation: Ames Laboratory-USDOE, IA.
authors.forename: M
authors.initials: M
authors.lastname: Suh
authors.forename: R
authors.initials: R
authors.lastname: Jankowiak
authors.forename: F
authors.initials: F
authors.lastname: Ariese
authors.forename: B
authors.initials: B
authors.lastname: Mao
authors.forename: N E
authors.initials: NE
authors.lastname: Geacintov
authors.forename: G J
authors.initials: GJ
authors.lastname: Small
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000737:chemistry*; D001483:Base Sequence; D001564:Benzo(a)pyrene / Q000494:pharmacology*; D001580:Benzopyrenes / Q000737:chemistry*; D003080:Cold Temperature; D018736:DNA Adducts / Q000737:chemistry*; D004249:DNA Damage; D004591:Electrophoresis, Polyacrylamide Gel; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry*
chemical_list: D001580:Benzopyrenes; D018736:DNA Adducts; D009841:Oligonucleotides; C043931:benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide-DNA; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D006147:Guanine; C051092:7-(7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo(a)-pyren-10-yl)guanine