Qin Aiping, Zhang Yan, Clark Melinda E, Moore Emily A, Rabideau Meaghan M, Moreau G Brett, Mann Barbara J
a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA.
Virulence. 2016 Nov 16;7(8):882-894. doi: 10.1080/21505594.2016.1168550. Epub 2016 Mar 30.
FipB, an essential virulence factor in the highly virulent Schu S4 strain of F. tularensis subsp. tularensis, shares sequence similarity with Disulfide Bond formation (Dsb) proteins, which can have oxidoreductase, isomerase, or chaperone activity. To further explore FipB's role in virulence potential substrates were identified by co-purification and 2D gel electrophoresis, followed by protein sequencing using mass spectrometry. A total of 119 potential substrates were identified. Proteins with predicted enzymatic activity were prevalent, and there were 19 proteins that had been previously identified as impacting virulence. Among the potential substrates were IglC, IglB, and PdpB, three components of the Francisella Type Six Secretion System (T6SS), which is also essential for virulence. T6SS are widespread in Gram-negative pathogens, but have not been reported to be dependent on Dsb-like proteins for assembly or function. The presented results suggest that FipB affects IglB and IglC substrates differently. In a fipB mutant there were differences in free sulfhydryl accessibility of IglC, but not IglB, when compared to wild-type bacteria. However, for both proteins FipB appears to act as a chaperone that facilitates proper folding and conformation. Understanding the role FipB plays the assembly and structure in this T6SS may reveal critical aspects of assembly that are common and novel among this widely distributed class of secretion systems.
FipB是土拉弗朗西斯菌亚种土拉弗朗西斯菌高毒力Schu S4菌株中的一种必需毒力因子，与二硫键形成（Dsb）蛋白具有序列相似性，Dsb蛋白可具有氧化还原酶、异构酶或伴侣活性。为了进一步探究FipB在毒力中的作用，通过共纯化和二维凝胶电泳鉴定潜在底物，随后使用质谱进行蛋白质测序。总共鉴定出119种潜在底物。具有预测酶活性的蛋白质很普遍，其中有19种蛋白质先前已被确定会影响毒力。潜在底物包括弗朗西斯菌VI型分泌系统（T6SS）的三个组分IglC、IglB和PdpB，T6SS对毒力也至关重要。T6SS广泛存在于革兰氏阴性病原体中，但尚未报道其组装或功能依赖于类Dsb蛋白。所呈现的结果表明FipB对IglB和IglC底物的影响不同。与野生型细菌相比，在fipB突变体中，IglC的游离巯基可及性存在差异，但IglB没有。然而，对于这两种蛋白质，FipB似乎都起到伴侣作用，促进正确折叠和构象形成。了解FipB在该T6SS的组装和结构中所起的作用，可能会揭示这类广泛分布的分泌系统中常见和新颖的组装关键方面。
