PDF(Pubmed)
Abstract：
The type VIIb protein secretion system (T7SSb) plays a role in interbacterial competition in Gram-positive Firmicute bacteria and secretes various toxic effector proteins. The mechanism of secretion and the roles of numerous conserved genes within T7SSb gene clusters remain unknown. EsaD is a nuclease toxin secreted by the Staphylococcus aureus T7SSb, which forms a complex with its cognate immunity protein, EsaG, and chaperone EsaE. Encoded upstream of EsaD are three small secreted proteins, EsxB, EsxC and EsxD. Here we show that EsxBCD bind to the transport domain of EsaD and function as EsaD export factors. We report the first structural information for a complete T7SSb substrate pre-secretion complex. Cryo-EM of the EsaDEG trimer and the EsaDEG-EsxBCD hexamer shows that incorporation of EsxBCD confers a conformation comprising a flexible globular cargo domain attached to a long narrow shaft that is likely to be crucial for efficient toxin export.
摘要：
VIIb型蛋白分泌系统（T7SSb）在革兰氏阳性Firmicute细菌的细菌间竞争中起作用，并分泌各种毒性效应蛋白。T7SSb基因簇中许多保守基因的分泌机制和作用仍然未知。EsaD是金黄色葡萄球菌T7SSb分泌的核酸酶毒素，与其同源免疫蛋白形成复合物，EsaG,和陪护EsaE.EsaD上游编码的是三个小的分泌蛋白，EsxB,EsxC和EsxD.在这里，我们显示EsxBCD与EsaD的传输域结合，并充当EsaD导出因子。我们报告了完整的T7SSb底物分泌前复合物的第一个结构信息。EsaDEG三聚体和EsaDEG-EsxBCD六聚体的Cryo-EM表明，EsxBCD的掺入赋予了包含柔性球状货物结构域的构象，该结构域附着在长而窄的轴上，这对于有效的毒素输出至关重要。
