Hooda Yogesh, Lai Christine C L, Moraes Trevor F
Department of Biochemistry, University of TorontoToronto, ON, Canada.
Front Cell Infect Microbiol. 2017 May 31;7:207. doi: 10.3389/fcimb.2017.00207. eCollection 2017.
The surfaces of many Gram-negative bacteria are decorated with soluble proteins anchored to the outer membrane via an acylated N-terminus; these proteins are referred to as surface lipoproteins or SLPs. In , SLPs such as transferrin-binding protein B (TbpB) and factor-H binding protein (fHbp) are essential for host colonization and infection because of their essential roles in iron acquisition and immune evasion, respectively. Recently, we identified a family of outer membrane proteins called Slam (Surface lipoprotein assembly modulator) that are essential for surface display of neisserial SLPs. In the present study, we performed a bioinformatics analysis to identify 832 Slam related sequences in 638 Gram-negative bacterial species. The list included several known human pathogens, many of which were not previously reported to possess SLPs. Hypothesizing that genes encoding SLP substrates of Slams may be present in the same gene cluster as the Slam genes, we manually curated neighboring genes for 353 putative Slam homologs. From our analysis, we found that 185 (~52%) of the 353 putative Slam homologs are located adjacent to genes that encode a protein with an N-terminal lipobox motif. This list included genes encoding previously reported SLPs in and , for which we were able to show that the neighboring Slams are necessary and sufficient to display these lipoproteins on the surface of . To further verify the authenticity of the list of predicted SLPs, we tested the surface display of one such Slam-adjacent protein from , a zoonotic pathogen. A robust Slam-dependent display of the protein was observed in the translocation assay indicating that the protein is a Slam-dependent SLP. Based on multiple sequence alignments and domain annotations, we found that an eight-stranded beta-barrel domain is common to all the predicted Slam-dependent SLPs. These findings suggest that SLPs with a TbpB-like fold are found widely in where they exist with their interaction partner Slam. In the future, SLPs found in pathogenic bacteria can be investigated for their role in virulence and may also serve as candidates for vaccine development.
许多革兰氏阴性菌的表面都装饰有通过酰化N端锚定在外膜上的可溶性蛋白质；这些蛋白质被称为表面脂蛋白或SLP。在淋病奈瑟菌中，诸如转铁蛋白结合蛋白B（TbpB）和因子H结合蛋白（fHbp）等SLP分别由于其在铁获取和免疫逃避中的重要作用，对于宿主定殖和感染至关重要。最近，我们鉴定了一类称为Slam（表面脂蛋白组装调节剂）的外膜蛋白，它们对于奈瑟菌SLP的表面展示至关重要。在本研究中，我们进行了生物信息学分析，以在638种革兰氏阴性细菌物种中鉴定出832个与Slam相关的序列。该列表包括几种已知的人类病原体，其中许多以前未报道过拥有SLP。假设编码Slam的SLP底物的基因可能与Slam基因存在于同一基因簇中，我们手动策划了353个假定的Slam同源物的邻近基因。从我们的分析中，我们发现353个假定的Slam同源物中有185个（约52%）位于编码具有N端脂盒基序的蛋白质的基因附近。该列表包括编码淋病奈瑟菌和脑膜炎奈瑟菌中先前报道的SLP的基因，我们能够证明邻近的Slam对于在淋病奈瑟菌表面展示这些脂蛋白是必要且充分的。为了进一步验证预测的SLP列表的真实性，我们测试了一种来自动物源性病原体猪链球菌的此类与Slam相邻的蛋白质的表面展示。在猪链球菌转位试验中观察到该蛋白质强烈的Slam依赖性展示，表明该蛋白质是一种Slam依赖性SLP。基于多序列比对和结构域注释，我们发现所有预测的Slam依赖性SLP都具有一个八链β桶结构域。这些发现表明，具有TbpB样折叠的SLP在革兰氏阴性菌中广泛存在，它们与它们的相互作用伙伴Slam一起存在。未来，可以研究病原菌中发现的SLP在毒力中的作用，它们也可能作为疫苗开发的候选物。
