Plant and Microbial Biology, University of California, Berkeley, CA 94704, USA.
Spruce Creek High School, Port Orange, FL 32127, USA.
Microbiology (Reading). 2018 Mar;164(3):338-348. doi: 10.1099/mic.0.000610. Epub 2018 Feb 5.
The needle structures of type III secretion (T3S) systems are formed by the secretion and polymerization of a needle subunit protein, YscF in Yersinia pestis. A subset of T3S systems employ unique heterodimeric chaperones, YscE and YscG in Y. pestis, to prevent the polymerization of needle subunits within the bacterial cell. We demonstrate that the YscE/YscG chaperone is also required for stable YscF expression and for secretion of YscF. Overexpression of a functional maltose-binding protein (MBP)-YscG hybrid protein stabilized cytoplasmic YscF but YscF was not secreted in the absence of YscE. Furthermore, a YscE mutant protein was identified that functioned with YscG to stabilize cytosolic YscF; however, YscF was not secreted. These findings confirm a role for the YscE/YscG chaperone in YscF secretion and suggest that YscE may have a specific role in this process. Recent studies have shown that YscF deleted of its N-terminal 15 residues is still secreted and functional, suggesting that YscF may not require an N-terminal secretion signal. However, we demonstrate that YscF contains an N-terminal secretion signal and that a functional N-terminal signal is required for YscF secretion.
III 型分泌系统（T3S）的针状结构是由分泌和聚合针状亚基蛋白 YscF 形成的，鼠疫耶尔森氏菌中的 YscF。一组 T3S 系统使用独特的异二聚体伴侣蛋白 YscE 和 YscG，以防止细菌细胞内针状亚基的聚合。我们证明 YscE/YscG 伴侣蛋白对于稳定 YscF 的表达和 YscF 的分泌也是必需的。功能性麦芽糖结合蛋白（MBP）-YscG 杂合蛋白的过表达稳定了细胞质 YscF，但在没有 YscE 的情况下 YscF 未被分泌。此外，鉴定出一种 YscE 突变蛋白，它与 YscG 一起发挥作用以稳定细胞溶质 YscF；然而，YscF 未被分泌。这些发现证实了 YscE/YscG 伴侣蛋白在 YscF 分泌中的作用，并表明 YscE 在该过程中可能具有特定的作用。最近的研究表明，缺失其 N 端 15 个残基的 YscF 仍可被分泌并具有功能，这表明 YscF 可能不需要 N 端分泌信号。然而，我们证明 YscF 包含一个 N 端分泌信号，并且功能性 N 端信号对于 YscF 的分泌是必需的。
