Application Of Nmr Spectroscopy In Chemical And Biochemi

苯并[a]芘(BaP)被认为通过与DNA中脱氧鸟苷(DG)的外环N-2或脱氧腺苷(Da)的N-6共价结合而启动细胞转化。这些相互作用是由代谢性来源于BaP的高活性湾区二醇环氧化物(DE)介导的。在一个给定的碱基上，总共可能有八个异构体BaP-DE加合物。据报道，不同的BaP-DE加合物具有不同的致突变活性。由于细胞突变被认为是在DES与DNA结合时开始的，突变变异很可能是源于这些bap DE加合物的构象差异。我们一直在使用2D核磁共振来确定由特定DES形成的DNA DA加合物的溶液结构。我们目前的核磁共振研究首次成功地确定了含有BaP DE的(10S)-da加合物的完全互补的DNA二聚体的结构，即来自(+)-(7S，8R，9S，10R)-7，8-dihydroxy-9，10-epoxy-7，8，9，10-tetrahydrobenzo[a]pyrene[(+)-bapDE1]的反式开放加合物。到目前为止，所有检查的DE-da加合物都显示碳氢化合物嵌入到DNA双链中。R构型加合物的烃类部分插入到修饰DA的5‘端，而S构型加合物的烃部分插入到3’端。这与DE-DG加合物形成对比。核磁共振研究表明，BaP-DES的反式开环DG加合物和相应的顺式开环DG加合物的小凹槽中的碳氢化合物与修饰的鸟嘌呤及其互补胞嘧啶碱基的置换是插层的。我们目前对从BaP-DES衍生的DA加合物的核磁共振研究表明，这些加合物的糖苷键周围存在着正反构象相互转化。含有DE加合物的寡核苷酸构象异构体的相互转化可能是单一加合物引起多种类型突变的原因

Benzo[a]pyrene (BaP) is believed to initiate cell transformation through covalent binding with the exocyclic N-2 of deoxyguanosine (dG) or N-6 of deoxyadenosine (dA) in DNA. These interactions are mediated by highly reactive bay-region diol epoxides (DE) metabolically derived from BaP. A total of eight isomeric BaP DE adducts are possible at a given base. Differences in mutagenic activities have been reported among various BaP DE adducts. Since cell mutation is believed to commence upon binding of DEs to DNA, the mutagenic variation are most likely arising from conformational differences rooted in these BaP DE adducts. We have been using 2D NMR to determine solution structures of DNA dA adducts formed from specific DEs. Our current NMR study constitutes the first successful structure determination of a fully complementary DNA duplex containing a (10S)-dA adduct of a BaP DE, namely, the trans opened adduct derived from (+)-(7S,8R,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-BaP DE1]. All DE-dA adducts examined to date show hydrocarbon intercalation into the DNA duplex. The hydrocarbon portion of adducts with R configuration at the site of attachment to the adenine base inserts toward the 5'-end of the modified dA, whereas the hydrocarbon in adducts with S configuration inserts towrd the 3'-end. This is in contrast to DE-dG adducts. The NMR studies have revealed that the hydrocarbon oriented in the minor groove for the trans opened dG adducts of BaP DEs, and the corresponding cis opened dG adducts are intercalated with displacement of the modified guanine and its complementary cytosine base. Our current NMR studies of dA adducts derived from BaP DEs have shown the presence of syn-anti conformational interconversion around the glycosidic bonds of these adducts. Interconversion of conformational isomers of oligonucleotides containing DE adducts has been suggested as possibly contributing to multiple types of mutations induced by a single adduct