The Gram-positive lactic acid bacterium Lactobacillus buchneri CD034 is covered by a two-dimensional crystalline, glycoproteinaceous cell surface (S-) layer lattice. While lactobacilli are extensively exploited as cell surface display systems for applied purposes, questions about how they stick their cell wall together are remaining open. This also includes the identification of the S-layer cell wall ligand. In this study, lipoteichoic acid was isolated from the L. buchneri CD034 cell wall as a significant fraction of the bacterium’s cell wall glycopolymers, structurally characterized and analyzed for its potential to mediate binding of the S-layer to the cell wall. Combined component analyses and 1D- and 2D-nuclear magnetic resonance spectroscopy (NMR) revealed the lipoteichoic acid to be composed of on average 31 glycerol-phosphate repeating units partially substituted with α-d-glucose, and with an α-d-Galp(1→2)-α-d-Glcp(1→3)−1,2-diacyl-sn-Gro glycolipid anchor. The specificity of binding between the L. buchneri CD034 S-layer protein and purified lipoteichoic acid as well as their interaction force of about 45 pN were obtained by single-molecule force spectroscopy; this value is in the range of typical ligand–receptor interactions. This study sheds light on a functional implication of Lactobacillus cell wall architecture by showing direct binding between lipoteichoic acid and the S-layer of L. buchneri CD034.

中文翻译：

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脂蛋白酸介导乳杆菌S层蛋白的结合

革兰氏阳性乳酸菌布氏乳杆菌CD034被二维结晶的糖蛋白细胞表面（S-）层晶格覆盖。尽管乳杆菌被广泛用作细胞表面展示系统以用于应用目的，但有关它们如何将其细胞壁粘在一起的问题仍然悬而未决。这还包括对S层细胞壁配体的鉴定。在这项研究中，从布氏乳杆菌中分离出脂磷壁酸CD034细胞壁是细菌细胞壁糖聚合物的重要组成部分，在结构上进行了表征，并分析了其介导S层与细胞壁结合的潜力。结合成分分析以及1D和2D核磁共振波谱（NMR），发现脂蛋白酸平均由31个甘油磷酸酯重复单元组成，部分被α- d-葡萄糖和α- d- Gal p取代（1→2）-α- d -Glc p（1→3）-1,2-二酰基SN -Gro糖脂锚。布氏乳杆菌之间结合的特异性通过单分子力谱获得CD034 S-层蛋白和纯化的脂磷壁酸及其相互作用力约为45 pN。该值在典型的配体-受体相互作用范围内。这项研究通过显示脂蛋白酸与布氏乳杆菌CD034的S层之间的直接结合，揭示了乳杆菌细胞壁结构的功能含义。