Caught in the act Proton-coupled electron transfer (PCET) is an important process for moving electrons through proteins and requires precise positioning of suitable proton and electron carriers. Kang et al. determined a cryo–electron microscopy structure of the active complex formed by ribonucleotide reductase that allows for PCET between two protein subunits over a total distance of ∼35 angstroms. Several interventions that stabilized the radical en route also stabilized the complex and allowed for visualization of the interface between the two subunits and the full network of residues that permit PCET. Science, this issue p. 424 A structure of the long-range radical transfer pathway within a ribonucleotide reductase is reported. Ribonucleotide reductases (RNRs) are a diverse family of enzymes that are alone capable of generating 2′-deoxynucleotides de novo and are thus critical in DNA biosynthesis and repair. The nucleotide reduction reaction in all RNRs requires the generation of a transient active site thiyl radical, and in class I RNRs, this process involves a long-range radical transfer between two subunits, α and β. Because of the transient subunit association, an atomic resolution structure of an active α2β2 RNR complex has been elusive. We used a doubly substituted β2, E52Q/(2,3,5)-trifluorotyrosine122-β2, to trap wild-type α2 in a long-lived α2β2 complex. We report the structure of this complex by means of cryo–electron microscopy to 3.6-angstrom resolution, allowing for structural visualization of a 32-angstrom-long radical transfer pathway that affords RNR activity.

中文翻译：

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核糖核苷酸还原酶全复合物中捕获的自由基转移途径的结构

质子耦合电子转移 (PCET) 是在蛋白质中移动电子的重要过程，需要精确定位合适的质子和电子载体。康等人。确定了由核糖核苷酸还原酶形成的活性复合物的低温电子显微镜结构，该复合物允许两个蛋白质亚基之间的 PCET 总距离约为 35 埃。一些在途中稳定自由基的干预措施也稳定了复合物，并允许两个亚基之间的界面和允许 PCET 的完整残基网络的可视化。科学，这个问题 p。424 报道了核糖核苷酸还原酶内长程自由基转移途径的结构。核糖核苷酸还原酶 (RNR) 是一个多样化的酶家族，它们单独能够从头生成 2'-脱氧核苷酸，因此在 DNA 生物合成和修复中至关重要。所有 RNR 中的核苷酸还原反应都需要产生瞬时活性位点硫基自由基，而在 I 类 RNR 中，该过程涉及两个亚基 α 和 β 之间的长程自由基转移。由于瞬态亚基关联，活性α2β2 RNR 复合物的原子分辨率结构一直难以捉摸。我们使用双取代的 β2，E52Q/(2,3,5)-三氟酪氨酸 122-β2，将野生型 α2 捕获在长寿命的 α2β2 复合物中。我们通过低温电子显微镜报告了这种复合物的结构，分辨率为 3.6 埃，