Sequence- and stereospecific conformational rearrangement of styrene oxide adducts located at A x C mismatched base pairs.
Sequence- and stereospecific conformational rearrangement of styrene oxide adducts located at A x C mismatched base pairs.
复制标题
位于 A x C 不匹配碱基对处的氧化苯乙烯加合物的序列和立体特异性构象重排。
DOI：
10.1021/bi992080t
复制
发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
Stone,MP
中科院分区：
文献类型：
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作者：
Simeonov,MF;Tamura,PJ;Wilkinson,AS;Harris,CM;Harris,TM;Stone,MP
测定了与胞嘧啶不匹配的R-和S-α-(N6-腺基)-环氧苯乙烷加合物X7in d(CGGACAXGAAG)·d(CTTCCTGTCCG)的溶液结构。这些是R-和S(61，3)C加合物。这些不匹配加合物的结构不同于序列同分异构体R-和S(61，2)C加合物[Painter，S.L.，Zegar，I.S.，Tamura，P.J.，Bluhm，S.，Harris，C.M.，Harris，T.M.，以及Stone，M.P.(1999)BioChemical 38,8635−8646]。结果表明，与R-和S-α-SO加合物相反的胞嘧啶错配的结构后果随着DNA序列的不同而不同。R-和S(61，3)C错配加合物的热力学稳定性与pH有关。在中性pH条件下，与R-和S(61，2)C加合物相比，R-和S(61，3)C加合物具有明显的结构微扰和较低的Tm值。在这两种情况下，这归因于围绕C6−N6键的重新取向，使得N6H质子背离嘌呤碱基的Watson−克里克面而进入主槽。从RMD计算中预测了N6−Cα−Cβ−O扭转角的构象，该构象由病变部位的苯乙烯羟基部分与腺嘌呤N6之间的N/O Guche型相互作用稳定。对于R(61，3)C加合物，苯乙烯基部分保持在主槽中取向，面向3‘-方向。在完全碱基配对的R(61，3)加合物中，它面向5‘方向。对于S(61，3)C加合物，苯环被插入到双链中，大致垂直于DNA的螺旋轴。它朝向5‘方向。在适当碱基配对的S(61，3)加合物中，它面向3‘-方向。这一结果与体内的定点突变实验相关联。后者显示R-和S(61，3)-α-环氧苯乙烷加合物无致突变性。这可能是由于与S(61，2)加合物相比，R-和S(61，3)加合物在中性pH下形成胞嘧啶错配而产生更大的结构扰动，后者表现出低水平的A→G突变。
The solution structures of R- and S-α-(N6-adenyl)-styrene oxide adducts mismatched with cytosine at position X7in d(CGGACAXGAAG)·d(CTTCCTGTCCG), incorporating codons 60, 61 (underlined), and 62 of the humanN-rasprotooncogene, were determined. These were the R- and S(61,3)C adducts. The structures for these mismatched adducts differed from the sequence isomeric R- and S(61,2)C adducts [Painter, S. L., Zegar, I. S., Tamura, P. J., Bluhm, S., Harris, C. M., Harris, T. M., and Stone, M. P. (1999)Biochemistry 38, 8635−8646]. The results reveal that the structural consequences of cytosine mispairing opposite the R- and S-α-SO adducts differ as a function of DNA sequence. The thermodynamic stability of both the R- and S(61,3)C mismatched adducts was dependent upon pH. At neutral pH, the R- and S(61,3)C adducts exhibited significant structural perturbation and had lowerTmvalues, as compared to the R- and S(61,2)C adducts. In both instances, this was attributed to reorientation about the C6−N6bond, such that the N6H proton faced away from the Watson−Crick face of the purine base and into the major groove. The conformation about the N6−Cα−Cβ−O torsion angle was predicted from rMD calculations to be stabilized by a N/O gauche-type interaction between the styrenyl hydroxyl moiety and adenine N6at the lesion site. For the R(61,3)C adduct, the styrenyl moiety remained oriented in the major groove and faced in the 3‘-direction. In the properly base-paired R(61,3) adduct, it had faced in the 5‘ direction. For the S(61,3)C adduct, the styrene ring was inserted into the duplex, approximately perpendicular to the helical axis of the DNA. It faced in the 5‘-direction. In the properly base-paired S(61,3) adduct, it had faced in the 3‘-direction. The results were correlated with site-specific mutagenesis experiments in vivo. The latter revealed that the R- and S(61,3)-α-styrene oxide adducts were nonmutagenic. This may be a consequence of the greater structural perturbation associated with formation of the cytosine mismatch at neutral pH for the R- and S(61,3) adducts as compared to the S(61,2) adduct that exhibited low levels of A → G mutations.