Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Department of Microbiology, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden.
Microbiology (Reading). 2010 Nov;156(Pt 11):3368-3378. doi: 10.1099/mic.0.043265-0. Epub 2010 Sep 16.
Mucus-binding proteins (MUBs) have been revealed as one of the effector molecules involved in mechanisms of the adherence of lactobacilli to the host; mub, or mub-like, genes are found in all of the six genomes of Lactobacillus reuteri that are available. We recently reported the crystal structure of a Mub repeat from L. reuteri ATCC 53608 (also designated strain 1063), revealing an unexpected recognition of immunoglobulins. In the current study, we explored the diversity of the ATCC 53608 mub gene, and MUB expression levels in a large collection of L. reuteri strains isolated from a range of vertebrate hosts. This analysis revealed that the MUB was only detectable on the cell surface of two highly related isolates when using antibodies that were raised against the protein. There was considerable variation in quantitative mucus adhesion in vitro among L. reuteri strains, and mucus binding showed excellent correlation with the presence of cell-surface ATCC 53608 MUB. ATCC 53608 MUB presence was further highly associated with the autoaggregation of L. reuteri strains in washed cell suspensions, suggesting a novel role of this surface protein in cell aggregation. We also characterized MUB expression in representative L. reuteri strains. This analysis revealed that one derivative of strain 1063 was a spontaneous mutant that expressed a C-terminally truncated version of MUB. This frameshift mutation was caused by the insertion of a duplicated 13 nt sequence at position 4867 nt in the mub gene, producing a truncated MUB also lacking the C-terminal LPxTG region, and thus unable to anchor to the cell wall. This mutant, designated 1063N (mub-4867(i)), displayed low mucus-binding and aggregation capacities, further providing evidence for the contribution of cell-wall-anchored MUB to such phenotypes. In conclusion, this study provided novel information on the functional attributes of MUB in L. reuteri, and further demonstrated that MUB and MUB-like proteins, although present in many L. reuteri isolates, show a high genetic heterogeneity among strains.
黏液结合蛋白（MUBs）已被揭示为参与乳杆菌黏附宿主机制的效应分子之一；mub 或 mub 样基因存在于可获得的 6 个乳酸杆菌属 reuteri 基因组中。我们最近报道了来自乳酸杆菌属 reuteri ATCC 53608（也称为 1063 株）的 Mub 重复结构的晶体结构，揭示了对免疫球蛋白的意外识别。在当前的研究中，我们探索了 ATCC 53608 mub 基因的多样性，以及从各种脊椎动物宿主中分离的大量乳酸杆菌属 reuteri 菌株中的 MUB 表达水平。这项分析表明，当使用针对该蛋白产生的抗体时，只有两种高度相关的分离株的细胞表面才能检测到 MUB。在体外，乳杆菌属 reuteri 菌株之间的黏液黏附定量差异很大，并且黏液结合与细胞表面 ATCC 53608 MUB 的存在显示出极好的相关性。ATCC 53608 MUB 的存在与乳杆菌属 reuteri 菌株在洗涤细胞悬浮液中的自动聚集高度相关，这表明这种表面蛋白在细胞聚集中具有新的作用。我们还对代表性的乳酸杆菌属 reuteri 菌株中的 MUB 表达进行了表征。该分析表明，1063 株的一个衍生物是一个自发突变体，表达 MUB 的 C 末端截断版本。这种移码突变是由 mub 基因中 4867 位核苷酸插入一个重复的 13 nt 序列引起的，产生一个也缺乏 C 末端 LPxTG 区域的截断 MUB，因此无法锚定在细胞壁上。该突变体命名为 1063N（mub-4867(i)），表现出低黏液结合和聚集能力，进一步为细胞壁锚定 MUB 对这些表型的贡献提供了证据。总之，本研究提供了关于乳酸杆菌属 reuteri 中 MUB 功能属性的新信息，并进一步证明 MUB 和 MUB 样蛋白虽然存在于许多乳酸杆菌属 reuteri 分离株中，但在菌株之间表现出高度的遗传异质性。
