Department of Biology , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.
ACS Chem Biol. 2018 May 18;13(5):1388-1397. doi: 10.1021/acschembio.8b00293. Epub 2018 Apr 9.
PccA and SenC are periplasmic copper chaperones required for the biogenesis of cbb-type cytochrome c oxidase ( cbb-Cox) in Rhodobacter capsulatus at physiological Cu concentrations. However, both proteins are dispensable for cbb-Cox assembly when the external Cu concentration is high. PccA and SenC bind Cu using Met and His residues and Cys and His residues as ligands, respectively, and both proteins form a complex during cbb-Cox biogenesis. SenC also interacts directly with cbb-Cox, as shown by chemical cross-linking. Here we determined the periplasmic concentrations of both proteins in vivo and analyzed their Cu binding stoichiometries and their Cu(I) and Cu(II) binding affinity constants ( K) in vitro. Our data show that both proteins bind a single Cu atom with high affinity. In vitro Cu transfer assays demonstrate Cu transfer both from PccA to SenC and from SenC to PccA at similar levels. We conclude that PccA and SenC constitute a Cu relay system that facilitates Cu delivery to cbb-Cox.
在生理铜浓度下，PccA 和 SenC 是 Rhodobacter capsulatus 中 cbb 型细胞色素 c 氧化酶（cbb-Cox）生物发生所需的周质铜伴侣。然而，当外部铜浓度较高时，这两种蛋白质对于 cbb-Cox 组装都是可有可无的。PccA 和 SenC 分别使用 Met 和 His 残基和 Cys 和 His 残基作为配体结合 Cu，并且这两种蛋白质在 cbb-Cox 生物发生过程中形成复合物。SenC 还与 cbb-Cox 直接相互作用，如化学交联所示。在这里，我们在体内确定了这两种蛋白质的周质浓度，并分析了它们的 Cu 结合化学计量比及其 Cu(I)和 Cu(II)结合亲和力常数（K）在体外。我们的数据表明，这两种蛋白质都以高亲和力结合单个 Cu 原子。体外 Cu 转移实验表明，从 PccA 到 SenC 和从 SenC 到 PccA 的 Cu 转移水平相似。我们得出结论，PccA 和 SenC 构成了一个 Cu 传递系统，有助于将 Cu 递送到 cbb-Cox。
