Investigation of the role of the BAM complex and SurA chaperone in outer-membrane protein biogenesis and type III secretion system expression in Salmonella
Investigation of the role of the BAM complex and SurA chaperone in outer-membrane protein biogenesis and type III secretion system expression in Salmonella
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DOI：
10.1099/mic.0.025155-0
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发表时间：
2009-05-01
期刊：
影响因子：
2.8
通讯作者：
Virlogeux-Payant, Isabelle
中科院分区：
文献类型：
--
作者：
Fardini, Yann;Trotereau, Jerome;Virlogeux-Payant, Isabelle
在大肠杆菌中，外膜蛋白(OMP)的组装需要BAM复合体和周质伴侣，如SurA或DegP。以前的工作表明，OMP组装和编码III型分泌系统的基因表达之间存在潜在的联系。为了验证这一假设，我们研究了BAM复合体的不同脂蛋白(即BAMB、BAMC、BAMD和BAME)以及周质伴侣SurA和DegP在沙门氏菌这两种表型中的作用。对相应缺失突变体的分析表明，与Delta Bamb突变体一样，BAMD、SurA和BAME在肠炎沙门氏菌的外膜生物发生中起着较小的作用，而Delta BAMC和Delta des P突变体对外膜生物发生的影响不明显。有趣的是，我们发现BAMD在沙门氏菌中不是必需的，不像它在大肠杆菌和淋病奈瑟菌中的同源物。相反，BAMD是完全表达T3SS-1和鞭毛所需的唯一蛋白质，这一点通过对参与这些T3SS生物合成的基因的转录分析证明。与这一发现一致的是，BAMD突变体显示这些T3SS分泌的效应蛋白减少，侵袭HT-29细胞的能力降低。由于Delta Sura和Delta BAME突变体的外膜OMPS水平较低，但T3SS-1和鞭毛的表达没有变化，这些结果表明OMP组装缺陷和T3SSs在沙门氏菌中的下调之间缺乏系统性联系；因此，这种联系似乎与更具体的机制有关，至少涉及BAMB和BAMD。
In Escherichia coli, the assembly of outer-membrane proteins (OMP) requires the BAM complex and periplasmic chaperones, such as SurA or DegP. Previous work has suggested a potential link between OMP assembly and expression of the genes encoding type-III secretion systems. In order to test this hypothesis, we studied the role of the different lipoproteins of the BAM complex (i.e. BamB, BamC, BamD and BamE), and the periplasmic chaperones SurA and DegP, in these two phenotypes in Salmonella. Analysis of the corresponding deletion mutants showed that, as previously described with the Delta bamB mutant, BamD, SurA and, to a lesser extent, BamE play a role in outer-membrane biogenesis in Salmonella Enteritidis, while the membrane was not notably disturbed in Delta bamC and Delta degP mutants. Interestingly, we found that BamD is not essential in Salmonella, unlike its homologues in Escherichia coli and Neisseria gonorrhoeae. In contrast, BamD was the only protein required for full expression of T3SS-1 and flagella, as demonstrated by transcriptional analysis of the genes involved in the biosynthesis of these T3SSs. In line with this finding, bamD mutants showed a reduced secretion of effector proteins by these T3SSs, and a reduced ability to invade HT-29 cells. As Delta surA and Delta bamE mutants had lower levels of OMPs in their outer membrane, but showed no alteration in T3SS-1 and flagella expression, these results demonstrate the absence of a systematic link between an OMP assembly defect and the downregulation of T3SSs in Salmonella; therefore, this link appears to be related to a more specific mechanism that involves at least BamB and BamD.