Setayesh F R, DeCorte B L, Horton P, Harris C M, Harris T M, Stone M P
Department of Chemistry and Center in Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235, USA.
Chem Res Toxicol. 1998 Jul;11(7):766-77. doi: 10.1021/tx9800147.
The R- and S-alpha-(N2-guanyl)styrene oxide (SO) adducts at X5 in d(G1G2C3A4X5G6T7G8G9T10G11).d(C12A13C14C15A16C17C18T19G20C21C22 ), encompassing codon 12 of the human N-ras protooncogene (underlined), were examined using 1H NMR spectroscopy. These were the R(12,1) and S(12,1) adducts, indicating the location of the R or S adduct at the first position of codon 12. These differed from the R- and S(12, 2)-alpha-SO adducts [Zegar, I. S., Setayesh, F. R., DeCorte, B. L., Harris, C. M., Harris, T. M., and Stone, M. P. (1996) Biochemistry 35, 4334-4348] in that the base pair 5' to the lesion was changed from G.C to A.T, while the base pair 3' to the lesion was changed from T.A to G.C. Comparison of the R- and S(12,1) adducts with the R- and S(12,2) adducts allowed the effects of flanking bases on the conformations of the alpha-SO adducts to be examined. This change in flanking base affected the R-SO lesion. The R(12,1) adduct structure was disordered at the adduct site, and a refined structure could not be obtained. NOE and chemical shift data suggested that the styrenyl moiety was oriented in the minor groove and in the 3'-direction from the site of adduction. In contrast, this change in flanking base did not affect the S-SO lesion. The S(12,1) adduct yielded a refined structure, with the styrenyl moiety edgewise in the minor groove and oriented in the 5'-direction relative to the site of adduction. A total of 232 interproton distances, including 13 styrene-DNA distances, were obtained. A total of 12 NOE-restrained molecular dynamics calculations converged with pairwise root-mean-square deviation of 1.10 A. The sixth-root residual index between calculated and experimental NOE intensities was 8.0 x 10(-)2 A. The styrene aromatic protons appeared as three resonances, suggesting rapid rotation. The possibility of a hydrogen bond between the styrene hydroxyl and C18 O2 in the S(12,1) adduct could not be confirmed. This work illustrates the dual roles of stereochemistry and sequence in modulating the properties of guanine N2 alpha-SO adducts.
在d(G1G2C3A4X5G6T7G8G9T10G11).d(C12A13C14C15A16C17C18T19G20C21C22)中，位于X5处的R-和S-α-(N2-鸟嘌呤基)环氧苯乙烯(SO)加合物（涵盖人类N-ras原癌基因的第12密码子，下划线标注），通过1H NMR光谱进行了检测。这些是R(12,1)和S(12,1)加合物，表明R或S加合物位于第12密码子的第一位。它们与R-和S(12, 2)-α-SO加合物[Zegar, I. S., Setayesh, F. R., DeCorte, B. L., Harris, C. M., Harris, T. M., and Stone, M. P. (1996) Biochemistry 35, 4334 - 4348]的不同之处在于，损伤位点5'端的碱基对从G.C变为A.T，而损伤位点3'端的碱基对从T.A变为G.C。将R-和S(12,1)加合物与R-和S(12,2)加合物进行比较，使得能够研究侧翼碱基对α-SO加合物构象的影响。侧翼碱基的这种变化影响了R-SO损伤。R(12,1)加合物在加合物位点处结构无序，无法获得精细结构。NOE和化学位移数据表明，苯乙烯基部分位于小沟中且从加成位点沿3'方向排列。相比之下，侧翼碱基的这种变化并未影响S-SO损伤。S(12,1)加合物产生了一个精细结构，苯乙烯基部分以边缘方式位于小沟中且相对于加成位点沿5'方向排列。总共获得了232个质子间距离，包括13个苯乙烯-DNA距离。总共进行了1次NOE约束的分子动力学计算，收敛时的成对均方根偏差为1.10 Å。计算得到的和实验测得的NOE强度之间的六次方根残差指数为8.0×10(-)2 Å。苯乙烯芳环质子表现为三个共振峰，表明其快速旋转。无法证实S(12,1)加合物中苯乙烯羟基与C18 O2之间存在氢键的可能性。这项工作说明了立体化学和序列在调节鸟嘌呤N2α-SO加合物性质方面的双重作用。
