Etzold Sabrina, MacKenzie Donald A, Jeffers Faye, Walshaw John, Roos Stefan, Hemmings Andrew M, Juge Nathalie
Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK.
Mol Microbiol. 2014 May;92(3):543-56. doi: 10.1111/mmi.12574. Epub 2014 Apr 2.
The mucus layer covering the gastrointestinal tract is the first point of contact of the intestinal microbiota with the host. Cell surface macromolecules are critical for adherence of commensal bacteria to mucus but structural information is scarce. Here we report the first molecular and structural characterization of a novel cell-surface protein, Lar_0958 from Lactobacillus reuteri JCM 1112(T) , mediating adhesion of L. reuteri human strains to mucus. Lar_0958 is a modular protein of 133 kDa containing six repeat domains, an N-terminal signal sequence and a C-terminal anchoring motif (LPXTG). Lar_0958 homologues are expressed on the cell-surface of L. reuteri human strains, as shown by flow-cytometry and immunogold microscopy. Adhesion of human L. reuteri strains to mucus in vitro was significantly reduced in the presence of an anti-Lar_0958 antibody and Lar_0958 contribution to adhesion was further confirmed using a L. reuteri ATCC PTA 6475 lar_0958 KO mutant (6475-KO). The X-ray crystal structure of a single Lar_0958 repeat, determined at 1.5 Å resolution, revealed a divergent immunoglobulin (Ig)-like β-sandwich fold, sharing structural homology with the Ig-like inter-repeat domain of internalins of the food borne pathogen Listeria monocytogenes. These findings provide unique structural insights into cell-surface protein repeats involved in adhesion of Gram-positive bacteria to the intestine.
覆盖胃肠道的黏液层是肠道微生物群与宿主的首个接触点。细胞表面大分子对于共生细菌黏附于黏液至关重要，但相关结构信息却很匮乏。在此，我们报道了一种新型细胞表面蛋白Lar_0958的首个分子和结构特征，该蛋白来自罗伊氏乳杆菌JCM 1112(T)，介导罗伊氏乳杆菌人源菌株黏附于黏液。Lar_0958是一种133 kDa的模块化蛋白，包含六个重复结构域、一个N端信号序列和一个C端锚定基序（LPXTG）。流式细胞术和免疫金显微镜检测显示，Lar_0958同源物在罗伊氏乳杆菌人源菌株的细胞表面表达。在抗Lar_0958抗体存在的情况下，人源罗伊氏乳杆菌菌株在体外对黏液的黏附显著降低，并且使用罗伊氏乳杆菌ATCC PTA 6475 lar_0958基因敲除突变体（6475-KO）进一步证实了Lar_0958对黏附的作用。以1.5 Å分辨率测定的单个Lar_0958重复结构域的X射线晶体结构显示出一种不同寻常的免疫球蛋白（Ig）样β折叠结构，与食源性病原体单核细胞增生李斯特菌内化素的Ig样重复结构域具有结构同源性。这些发现为革兰氏阳性菌黏附于肠道所涉及的细胞表面蛋白重复结构域提供了独特的结构见解。
