Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, USA.
Virulence. 2010 Jul-Aug;1(4):260-72. doi: 10.4161/viru.1.4.12318.
Vibrio parahaemolyticus ExsA is the transcriptional regulator for type III secretion system 1 (T3SS1) while ExsD blocks T3SS1 expression. Herein we show that deletion of exsC from V. parahaemolyticus blocked synthesis of T3SS1-dependent proteins under inducing conditions (contact with HeLa cells), while in trans complementation of the ΔexsC strain with wild-type exsC restored protein synthesis. Under non-inducing conditions (Luria broth plus salt), in trans expression of exsC in a wild-type strain resulted in synthesis and secretion of T3SS1-dependent proteins. Deletion of exsC does not affect the synthesis of ExsA while expression of T3SS1 genes is independent of ExsC in the absence of ExsD. Co-expression of recombinant proteins with different antigenic tags demonstrated that ExsC binds ExsD and that the N-terminal amino acids of ExsC (positions 7 to 12) are required for binding. Co-expression and purification of antigentically tagged ExsA and ExsD demonstrated that ExsD directly binds ExsA and presumably prevents ExsA from binding promoter regions of T3SS1 genes. Collectively these data demonstrate that ExsD binds ExsA to block expression of T3SS1 genes, while ExsC binds ExsD to permit expression of T3SS1 genes. ExsA, ExsC, and ExsD from V. parahaemolyticus appear to be functional orthologues of their Pseudomonas aeruginosa counterparts.
副溶血性弧菌 ExsA 是 III 型分泌系统 1（T3SS1）的转录调控因子，而 ExsD 则阻止 T3SS1 的表达。在此，我们表明从副溶血性弧菌中缺失 exsC 会阻止 T3SS1 依赖蛋白在诱导条件下（与 HeLa 细胞接触）的合成，而在ΔexsC 菌株中用野生型 exsC 进行反式互补则恢复了蛋白合成。在非诱导条件下（Luria 肉汤加盐），在野生型菌株中转录表达 exsC 会导致 T3SS1 依赖蛋白的合成和分泌。缺失 exsC 不影响 ExsA 的合成，而在没有 ExsD 的情况下，T3SS1 基因的表达独立于 ExsC。具有不同抗原标签的重组蛋白的共表达表明，ExsC 与 ExsD 结合，而 ExsC 的 N 端氨基酸（位置 7 到 12）是结合所必需的。具有不同抗原标签的 ExsA 和 ExsD 的共表达和纯化表明，ExsD 直接与 ExsA 结合，并可能阻止 ExsA 与 T3SS1 基因的启动子区域结合。总之，这些数据表明 ExsD 与 ExsA 结合以阻止 T3SS1 基因的表达，而 ExsC 与 ExsD 结合以允许 T3SS1 基因的表达。副溶血性弧菌的 ExsA、ExsC 和 ExsD 似乎是其铜绿假单胞菌对应物的功能同源物。
