Nishimura Ryutaro, Abe Akio, Sakuma Yusuke, Kuwae Asaomi
Laboratory of Bacterial Infection, Graduate School of Infection Control Sciences, Kitasato University, 5-9-1 Shirokane, Minato, Tokyo 108-8641, Japan.
Microbiol Immunol. 2018 Dec;62(12):743-754. doi: 10.1111/1348-0421.12659. Epub 2018 Dec 14.
Bordetella species, including B. pertussis, have a type III secretion system that is highly conserved among gram-negative pathogenic bacteria. Genes encoding the component proteins of the type III secretion system are localized at the bsc locus in the Bordetella genome. Here, the function of a hypothetical protein Bcr4 encoded at the bsc locus in the B. bronchiseptica genome was investigated. A Bcr4-deficient mutant was created and the amounts of type III secreted proteins (e.g., BopB, BopN and Bsp22) in both the supernatant fraction and whole-cell lysates of the Bcr4-deficient mutant were determined. It was found that the amounts of these proteins were significantly lower than in the wild-type strain. The amounts of type III secreted proteins in the supernatant fraction and whole-cell lysates were much greater in a Bcr4-overproducing strain than in the wild-type strain. The type III secreted protein BspR reportedly negatively regulates the type III secretion system. Here, it was observed that a Bcr4 + BspR double-knockout mutant did not secrete type III secreted proteins, whereas the amounts of these proteins in whole-cell lysates of this mutant were nearly equal to those in whole-cell lysates of the BspR-deficient mutant. Bcr4 thus appears to play an essential role in the extracellular secretion of type III secreted proteins. Our data also suggest that Bcr4 antagonizes the negative regulatory function of BspR.
博德特氏菌属，包括百日咳博德特氏菌，拥有一种III型分泌系统，该系统在革兰氏阴性病原菌中高度保守。编码III型分泌系统组成蛋白的基因位于博德特氏菌基因组的bsc位点。在此，对支气管败血博德特氏菌基因组中bsc位点编码的一种假定蛋白Bcr4的功能进行了研究。构建了一个Bcr4缺陷型突变体，并测定了该突变体的上清液组分和全细胞裂解物中III型分泌蛋白（如BopB、BopN和Bsp22）的含量。结果发现，这些蛋白的含量显著低于野生型菌株。在Bcr4过量表达菌株中，上清液组分和全细胞裂解物中III型分泌蛋白的含量比野生型菌株高得多。据报道，III型分泌蛋白BspR对III型分泌系统起负调控作用。在此观察到，Bcr4 + BspR双敲除突变体不分泌III型分泌蛋白，而该突变体全细胞裂解物中这些蛋白的含量与BspR缺陷型突变体全细胞裂解物中的含量几乎相等。因此，Bcr4似乎在III型分泌蛋白的细胞外分泌中起关键作用。我们的数据还表明，Bcr4拮抗BspR的负调控功能。
