Protein secretion pathways in the phylum Bacteroidetes

拟杆菌属的成员是迄今为止人类肠道微生物组中最丰富的革兰氏阴性细菌。我们使用质谱法来检查外膜（OM）蛋白质组和分泌组的最常见的研究成员之一的拟杆菌属，B。fragilis，在实验室条件下生长。尽管我们没有发现任何新的分泌途径，但我们发现这种生物体使用的分泌策略与变形菌（例如大肠杆菌）非常不同。杆菌B。fragilis缺乏许多在变形杆菌中广泛存在的途径（例如，II、III和IV型途径），但同时产生多个I型分泌系统。I型途径的底物是未知的，并且不能基于与变形菌门中的I型底物蛋白质的同源性容易地预测。B。fragilis与Proteobacteria的显著不同之处还在于它产生大量暴露在细胞表面上的脂蛋白。我们目前正在使用各种方法来研究脂蛋白在OM中转运的机制，并确定标记特定脂蛋白用于输出的靶向信号。有趣的是，在分泌组中发现的许多蛋白质与Genbank数据库中的蛋白质缺乏显著的同源性，并且可能具有新的功能。

Members of the genus Bacteroides are by far the most abundant Gram-negative bacteria in the human gut microbiome. We used mass spectrometry to examine the outer membrane (OM) proteome and secretome of one of the most commonly studied members of the Bacteroides genus, B. fragilis, grown under laboratory conditions. Although we did not identify any novel secretion pathways, we found that this organism uses a very different range of secretion strategies than Proteobacteria such as E. coli. B. fragilis lacks many of the pathways that are widespread among the Protebacteria (e.g., the type II, III and IV pathways) but produces multiple type I secretion systems simultaneously. The substrates of the type I pathways are unknown and cannot be easily predicted based on homology to proteins that are type I substrates in Proteobacteria. B. fragilis also differs dramatically from Proteobacteria in that it produces a large number of lipoproteins that are exposed on the cell surface. We are currently using a variety of methods to investigate the mechanism(s) by which lipoproteins are transported across the OM and identifying targeting signals that earmark specific lipoproteins for export. Interestingly, many of the proteins found in the secretome lack significant homology to proteins that are in the Genbank database and presumably have novel functions.