Department of Microbiology, University of Chicago, IL 60637, USA.
BMC Microbiol. 2012 Sep 25;12:219. doi: 10.1186/1471-2180-12-219.
Staphylococcus aureus secretes EsxA and EsxB, two small polypeptides of the WXG100 family of proteins. Genetic analyses have shown that production and secretion of EsxA and EsxB require an intact ESAT-6 Secretion System (ESS), a cluster of genes that is conserved in many Firmicutes and encompasses esxA and esxB . Here, we characterize EssB, one of the proteins encoded by the ESS cluster. EssB is highly conserved in Gram-positive bacteria and belongs to the Cluster of Orthologous Groups of protein COG4499 with no known function.
By generating an internal deletion in essB , we demonstrate that EssB is required for secretion of EsxA. We use a polyclonal antibody to identify EssB and show that the protein fractionates with the plasma membrane of S. aureus . Yet, when produced in Escherichia coli, EssB remains mostly soluble and the purified protein assembles into a highly organized oligomer that can be visualized by electron microscopy. Production of truncated EssB variants in wild-type S. aureus confers a dominant negative phenotype on EsxA secretion.
The data presented here support the notion that EssB may oligomerize and interact with other membrane components to form the WXG100-specific translocon in S. aureus .
金黄色葡萄球菌分泌 EsxA 和 EsxB，这两种小的 WXG100 家族蛋白多肽。遗传分析表明，EsxA 和 EsxB 的产生和分泌需要一个完整的 ESAT-6 分泌系统（ESS），这是一组在许多 Firmicutes 中保守的基因，包含 esxA 和 esxB。在这里，我们描述了 ESS 簇编码的蛋白之一 EssB。EssB 在革兰氏阳性菌中高度保守，属于 COG4499 蛋白的同源簇，没有已知的功能。
通过在 essB 中产生内部缺失，我们证明 EssB 是 EsxA 分泌所必需的。我们使用多克隆抗体来鉴定 EssB，并表明该蛋白与金黄色葡萄球菌的质膜分离。然而，当在大肠杆菌中产生时，EssB 仍然主要是可溶的，并且纯化的蛋白组装成高度有序的寡聚物，可以通过电子显微镜观察到。在野生型金黄色葡萄球菌中产生截短的 EssB 变体赋予 EsxA 分泌显性负表型。
这里提出的的数据支持这样的观点，即 EssB 可能寡聚化并与其他膜成分相互作用，在金黄色葡萄球菌中形成 WXG100 特异性转位体。
