Department of Chemistry, University of California, Davis , Davis, California 95616, United States.
Department of Chemistry and Biochemistry, St. Cloud State University , St. Cloud, Minnesota 56301, United States.
J Am Chem Soc. 2018 Feb 7;140(5):1753-1759. doi: 10.1021/jacs.7b10860. Epub 2018 Jan 24.
7-Carboxy-7-deazaguanine (CDG) synthase (QueE), a member of the radical S-deoxyadenosyl-l-methionine (SAM) superfamily of enzymes, catalyzes a radical-mediated ring rearrangement required to convert 6-carboxy-5,6,7,8-tetrahydropterin (CPH) into CDG, forming the 7-dezapurine precursor to all pyrrolopyrimidine metabolites. Members of the radical SAM superfamily bind SAM to a [4Fe-4S] cluster, leveraging the reductive cleavage of SAM by the cluster to produce a highly reactive 5'-deoxyadenosyl radical which initiates chemistry by H atom abstraction from the substrate. QueE has recently been shown to use 6-carboxypterin (6-CP) as an alternative substrate, forming 6-deoxyadenosylpterin as the product. This reaction has been proposed to occur by radical addition between 5'-dAdo· and 6-CP, which upon oxidative decarboxylation yields the modified pterin. Here, we present spectroscopic evidence for a 6-CP-dAdo radical. The structure of this intermediate is determined by characterizing its electronic structure by continuous wave and pulse electron paramagnetic resonance spectroscopy.
7-羧基-7-脱氮鸟嘌呤（CDG）合酶（QueE）是自由基 S-腺苷-L-甲硫氨酸（SAM）超家族酶的成员，催化一个自由基介导的环重排反应，该反应将 6-羧基-5,6,7,8-四氢蝶呤（CPH）转化为 CDG，形成所有吡咯并嘧啶代谢物的 7-去氮嘌呤前体。自由基 SAM 超家族成员将 SAM 结合到 [4Fe-4S] 簇上，利用簇还原裂解 SAM 产生高反应性的 5'-脱氧腺苷自由基，通过从底物中提取 H 原子引发化学反应。最近已经证明 QueE 可以将 6-羧基蝶呤（6-CP）用作替代底物，形成 6-脱氧腺苷蝶呤作为产物。该反应被认为是通过 5'-dAdo·和 6-CP 之间的自由基加成反应发生的，该反应在氧化脱羧后生成修饰的蝶呤。在这里，我们通过连续波和脉冲电子顺磁共振波谱学来表征其电子结构，提供了 6-CP-dAdo 自由基的光谱证据。通过表征其电子结构，确定了该中间体的结构。
