Merritt W Keither, Scholdberg Tandace A, Nechev Lubomir V, Harris Thomas M, Harris Constance M, Lloyd R Stephen, Stone Michael P
Department of Chemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, USA.
Chem Res Toxicol. 2004 Aug;17(8):1007-19. doi: 10.1021/tx049908j.
Butadiene is oxidized in vivo to form stereoisomeric butadiene diol epoxides (BDE). These react with adenine N(6) in DNA yielding stereoisomeric N(6)-(2,3,4-trihydroxybutyl)-2'-deoxyadenosyl (BDT) adducts. When replicated in Escherichia coli, the (2R,3R)-N(6)-(2,3,4-trihydroxybutyl)-2'-deoxyadenosyl adduct yielded low levels of A-->G mutations whereas the (2S,3S)-N(6)-(2,3,4-trihydroxybutyl)-2'-deoxyadenosyl butadiene triol adduct yielded low levels of A-->C mutations [Carmical, J. R., Nechev, L. V., Harris, C. M., Harris, T. M., and Lloyd, R. S. (2000) Environ. Mol. Mutagen. 35, 48-56]. Accordingly, the structure of the (2R,3R)-N(6)-(2,3,4-trihydroxybutyl)-2'-deoxyadenosyl adduct at position X(6) in d(CGGACXAGAAG).d(CTTCTTGTCCG), the ras61 R,R-BDT-(61,2) adduct, was compared to the corresponding structure for the (2S,3S)-N(6)-(2,3,4-trihydroxybutyl)-2'-deoxyadenosyl adduct in the same sequence, the ras61 S,S-BDT-(61,2) adduct. Both the R,R-BDT-(61,2) and S,S-BDT-(61,2) adducts are oriented in the major groove of the DNA, accompanied by modest structural perturbations. However, structural refinement of the two adducts using a simulated annealing restrained molecular dynamics (rMD) approach suggests stereospecific differences in hydrogen bonding between the hydroxyl groups located at the beta- and gamma-carbons of the BDT moiety, and T(17) O(4) of the modified base pair X(6).T(17). The rMD calculations predict hydrogen bond formation between the gamma-OH and the T(17) O(4) in the R,R-BDT-(61,2) adduct whereas in the S,S-BDT-(61,2) adduct, hydrogen bond formation is predicted between the beta-OH and the T(17) O(4). This difference positions the two adducts differently in the major groove. This may account for the differential mutagenicity of the two adducts and suggests that the two adducts may interact differentially with other DNA processing enzymes. With respect to mutagenesis in E. coli, the minimal perturbation of DNA induced by both major groove adducts correlates with their facile bypass by three E. coli DNA polymerases in vitro and may account for their weak mutagenicity [Carmical, J. R., Nechev, L. V., Harris, C. M., Harris, T. M., and Lloyd, R. S. (2000) Environ. Mol. Mutagen. 35, 48-56].
丁二烯在体内被氧化形成立体异构的丁二烯二醇环氧化物（BDE）。这些物质与DNA中的腺嘌呤N(6)反应，生成立体异构的N(6)-(2,3,4-三羟基丁基)-2'-脱氧腺苷（BDT）加合物。当在大肠杆菌中复制时，(2R,3R)-N(6)-(2,3,4-三羟基丁基)-2'-脱氧腺苷加合物产生低水平的A→G突变，而(2S,3S)-N(6)-(2,3,4-三羟基丁基)-2'-脱氧腺苷丁三醇加合物产生低水平的A→C突变[卡米卡尔，J.R.，涅切夫，L.V.，哈里斯，C.M.，哈里斯，T.M.，和劳埃德，R.S.（2000年）《环境分子突变》35卷，48 - 56页]。因此，将d(CGGACXAGAAG).d(CTTCTTGTCCG)中X(6)位置的(2R,3R)-N(6)-(2,3,4-三羟基丁基)-2'-脱氧腺苷加合物，即ras61 R,R-BDT-(61,2)加合物的结构，与相同序列中(2S,3S)-N(6)-(2,3,4-三羟基丁基)-2'-脱氧腺苷加合物，即ras61 S,S-BDT-(61,2)加合物的相应结构进行了比较。R,R-BDT-(61,2)和S,S-BDT-(61,2)加合物都位于DNA的大沟中，并伴有适度的结构扰动。然而，使用模拟退火约束分子动力学（rMD）方法对这两种加合物进行结构优化表明，位于BDT部分β-和γ-碳上的羟基与修饰碱基对X(6).T(17)的T(17) O(4)之间的氢键存在立体特异性差异。rMD计算预测在R,R-BDT-(61,2)加合物中γ-OH与T(17) O(4)之间形成氢键，而在S,S-BDT-(61,2)加合物中，预测β-OH与T(17) O(4)之间形成氢键。这种差异使得两种加合物在大沟中的位置不同。这可能解释了两种加合物的不同致突变性，并表明两种加合物可能与其他DNA加工酶有不同的相互作用。关于在大肠杆菌中的诱变作用，两种大沟加合物对DNA诱导的最小扰动与它们在体外被三种大肠杆菌DNA聚合酶轻易绕过相关，这可能解释了它们较弱的致突变性[卡米卡尔，J.R.，涅切夫，L.V.，哈里斯，C.M.，哈里斯，T.M.，和劳埃德，R.S.（2000年）《环境分子突变》35卷，48 - 56页]。
