The stereochemistry of benzo[a]pyrene-2′-deoxyguanosine adducts affects DNA methylation by SssI and HhaI DNA methyltransferases
The stereochemistry of benzo[a]pyrene-2′-deoxyguanosine adducts affects DNA methylation by SssI and HhaI DNA methyltransferases
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DOI：
10.1111/j.1742-4658.2007.05754.x
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发表时间：
2007-04-01
期刊：
影响因子：
5.4
通讯作者：
Gromova, Elizaveta S.
中科院分区：
文献类型：
--
作者：
Subach, Oksana M.;Maltseva, Diana V.;Gromova, Elizaveta S.
环境污染物苯并[a]芘(B[a]P)，(+)-7R，8S-二醇9S，10R-环氧化物的生物毒性代谢物与DNA中的鸟嘌呤发生化学反应，形成(+)-反式-B[a]P-N-2-DG，其次是(+)-顺式-B[a]P-N-2-DG加合物。在这里，我们比较了两个纯化的原核DNA甲基转移酶(MTase)SSSI和HHAI催化的加合物立体化学和构象对胞嘧啶甲基化的影响，这些病变分别位于其CG和GCGC识别位点内或附近。(+)-顺式-B[a]P-N-2-dG和(+)-反式-B[a]P-N-2-dG加合物的吡喃基残基的荧光性质有所增强，但增强程度不同，说明芳香族B[a]P残基在DNA-蛋白质复合体中处于不同的微环境中。我们先前已经证明，(+)-反异构体加合物抑制两种MTase的结合效率和甲基化效率(k(CAT))[Subach OM，Baskunov VB，Darii MV，Maltseva DV，Alexandrov DA，Kirsanova OV，Kolbanovski A，Kolbanovski M，Johnson F，Bonala R等人。(2006)生物化学45,6142-6159]。在这里，我们证明了立体异构体(+)-顺式-B[a]P-N-2-dG损伤对这些MTase的结合和对k(CAT)的影响很小。小沟槽(+)-反式加合物干扰正常DNA小沟槽的形成与MTase的催化环接触。然而，插层碱位移(+)-顺式加合物不会干扰DNA催化环的小槽接触，从而使MTase接近正常结合，并保持k(CAT)值不变。
The biologically most significant genotoxic metabolite of the environmental pollutant benzo[a]pyrene (B[a]P), (+)-7R,8S-diol 9S,10R-epoxide, reacts chemically with guanine in DNA, resulting in the predominant formation of (+)-trans-B[a]P-N-2-dG and, to a lesser extent, (+)-cis-B[a]P-N-2-dG adducts. Here, we compare the effects of the adduct stereochemistry and conformation on the methylation of cytosine catalyzed by two purified prokaryotic DNA methyltransferases (MTases), SssI and HhaI, with the lesions positioned within or adjacent to their CG and GCGC recognition sites, respectively. The fluorescence properties of the pyrenyl residues of the (+)-cis-B[a]P-N-2-dG and (+)-trans-B[a]P-N-2-dG adducts in complexes with MTases are enhanced, but to different extents, indicating that aromatic B[a]P residues are positioned in different microenvironments in the DNA-protein complexes. We have previously shown that the (+)-trans-isomeric adduct inhibits both the binding and methylating efficiencies (k(cat)) of both MTases [Subach OM, Baskunov VB, Darii MV, Maltseva DV, Alexandrov DA, Kirsanova OV, Kolbanovskiy A, Kolbanovskiy M, Johnson F, Bonala R, et al. (2006) Biochemistry45, 6142-6159]. Here we show that the stereoisomeric (+)-cis-B[a]P-N-2-dG lesion has only a minimal effect on the binding of these MTases and on k(cat). The minor-groove (+)-trans adduct interferes with the formation of the normal DNA minor-groove contacts with the catalytic loop of the MTases. However, the intercalated base-displaced (+)-cis adduct does not interfere with the minor-groove DNA-catalytic loop contacts, allowing near-normal binding of the MTases and undiminished k(cat) values.