O4-Alkyl-2′-deoxythymidine cross-linked DNA to probe recognition and repair by O6-alkylguanine DNA alkyltransferases
作者:Francis P. McManus、Derek K. O'Flaherty、Anne M. Noronha、Christopher J. Wilds
DOI:10.1039/c2ob25705j
日期:——
DNA duplexes containing a directly opposed O4-2â²-deoxythymidine-alkyl-O4-2â²-deoxythymidine (O4-dT-alkyl-O4-dT) interstrand cross-link (ICL) have been prepared by the synthesis of cross-linked nucleoside dimers which were converted to phosphoramidites to produce site specific ICL. ICL duplexes containing alkyl chains of four and seven methylene groups were prepared and characterized by mass spectrometry and nuclease digests. Thermal denaturation experiments revealed four and seven methylene containing ICL increased the Tm of the duplex with respect to the non-cross-linked control with an observed decrease in enthalpy based on thermodynamic analysis of the denaturation curves. Circular dichroism experiments on the ICL duplexes indicated minimal difference from B-form DNA structure. These ICL were used for DNA repair studies with O6-alkylguanine DNA alkyltransferase (AGT) proteins from human (hAGT) and E. coli (Ada-C and OGT), whose purpose is to remove O6-alkylguanine and in some cases O4-alkylthymine lesions. It has been previously shown that hAGT can repair O6-2â²-deoxyguanosine-alkyl-O6-2â²-deoxyguanosine ICL. The O4-dT-alkyl-O4-dT ICL prepared in this study were found to evade repair by hAGT, OGT and Ada-C. Electromobility shift assay (EMSA) results indicated that the absence of any repair by hAGT was not a result of binding. OGT was the only AGT to show activity in the repair of oligonucleotides containing the mono-adducts O4-butyl-4-ol-2â²-deoxythymidine and O4-heptyl-7-ol-2â²-deoxythymidine. Binding experiments conducted with hAGT demonstrated that the protein bound O4-alkylthymine lesions with similar affinities to O6-methylguanine, which hAGT repairs efficiently, suggesting the lack of O4-alkylthymine repair by hAGT is not a function of recognition.
通过合成交联核苷二聚体制备了含有直接对立的 O4-2â²-脱氧胸苷-烷基-O4-2â²-脱氧胸苷(O4-dT-烷基-O4-dT)链间交联(ICL)的 DNA 双链体。制备了含有四个和七个亚甲基的烷基链的 ICL 双链体,并通过质谱分析和核酸酶消化进行了表征。热变性实验表明,与未交联的对照组相比,含有四个和七个亚甲基的 ICL 提高了双链体的 Tm 值,根据变性曲线的热力学分析,焓值也有所降低。对 ICL 双链体进行的环二色性实验表明,它们与 B 型 DNA 结构的差异极小。这些 ICL 被用来与来自人类(hAGT)和大肠杆菌(Ada-C 和 OGT)的 O6-烷基鸟嘌呤 DNA 烷基转移酶(AGT)蛋白一起进行 DNA 修复研究。以前的研究表明,hAGT 可以修复 O6-2â²-脱氧鸟苷-烷基-O6-2â²-脱氧鸟苷 ICL。本研究中制备的 O4-dT-alkyl-O4-dT ICL 可逃避 hAGT、OGT 和 Ada-C 的修复。电迁移试验(EMSA)结果表明,hAGT 没有进行任何修复并不是因为结合的结果。在修复含有 O4-丁基-4-醇-2â²-脱氧胸苷和 O4-庚基-7-醇-2â²-脱氧胸苷的寡核苷酸时,OGT 是唯一显示出活性的 AGT。用 hAGT 进行的结合实验表明,该蛋白结合 O4-烷基胸腺嘧啶病变的亲和力与 hAGT 能有效修复的 O6-甲基鸟嘌呤相似,这表明 hAGT 缺乏对 O4-烷基胸腺嘧啶的修复功能并不是识别功能的问题。