Nitrogen mustards are among the first modern anticancer chemotherapeutics that are still widely used as non-specific anticancer alkylating agents. While the mechanism of action of mustard drugs involves the generation of DNA interstrand cross-links, the predominant lesions produced by these drugs are nitrogen half-mustard-N7-dG (NHMG) adducts. The bulky major groove lesion NHMG, if left unrepaired, can be bypassed by translesion synthesis (TLS) DNA polymerases. However, studies of the TLS past NHMG have not been reported so far. Here, we present the first synthesis of an oligonucleotide containing a site-specific NHMG. We also report kinetic and structural characterization of human DNA polymerase η (polη) bypassing NHMG. The templating NHMG slows dCTP incorporation ∼130-fold, while it increases the misincorporation frequency ∼10–30-fold, highlighting the promutagenic nature of NHMG. A crystal structure of polη incorporating dCTP opposite NHMG shows a Watson–Crick NHMG:dCTP base pair with a large propeller twist angle. The nitrogen half-mustard moiety fits snugly into an open cleft created by the Arg61–Trp64 loop of polη, suggesting a role of the Arg61–Trp64 loop in accommodating bulky major groove adducts during lesion bypass. Overall, our results presented here to provide first insights into the TLS of the major DNA adduct formed by nitrogen mustard drugs.

中文翻译：

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人类DNA聚合酶η的跨病变合成主要由氮芥引起的DNA病变

氮芥是最早的现代抗癌化学疗法之一，至今仍广泛用作非特异性抗癌烷基化剂。芥菜药的作用机理涉及DNA链间交联的产生，而这些药产生的主要病灶是氮半芥末-N7-dG（NHMG）加合物。如果不进行修复，则可以通过跨病变合成（TLS）DNA聚合酶绕过大的主要凹槽病变NHMG。但是，迄今为止尚未报道过NHMG之后的TLS研究。在这里，我们介绍了包含位点特异性NHMG的寡核苷酸的首次合成。我们还报告绕过NHMG的人类DNA聚合酶η（polη）的动力学和结构表征。模板NHMG使dCTP的掺入速度减慢了约130倍，而错配频率增加了约10-30倍，突出了NHMG的致突变性。掺有dCTP的polη的晶体结构与NHMG相反，显示出具有大螺旋桨扭曲角的Watson-Crick NHMG：dCTP碱基对。氮半芥末部分紧贴在由polη的Arg61–Trp64环产生的开放裂口中，表明Arg61–Trp64环在病变旁路中适应大体积主要凹槽加合物的作用。总的来说，我们在这里提出的结果提供了对氮芥子气药物形成的主要DNA加合物的TLS的初步了解。提示Arg61–Trp64环在病变旁路中适应大块主沟加合物的作用。总的来说，我们在这里提出的结果提供了对氮芥子气药物形成的主要DNA加合物的TLS的初步了解。提示Arg61–Trp64环在病变旁路中适应大块主沟加合物的作用。总的来说，我们在这里提出的结果提供了对氮芥子气药物形成的主要DNA加合物的TLS的初步了解。