Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, UK.
Structure. 2013 May 7;21(5):844-53. doi: 10.1016/j.str.2013.03.010. Epub 2013 Apr 25.
Many pathogenic bacteria encase themselves in a polysaccharide capsule that provides a barrier to the physical and immunological challenges of the host. The mechanism by which the capsule assembles around the bacterial cell is unknown. Wzi, an integral outer-membrane protein from Escherichia coli, has been implicated in the formation of group 1 capsules. The 2.6 Å resolution structure of Wzi reveals an 18-stranded β-barrel fold with a novel arrangement of long extracellular loops that blocks the extracellular entrance and a helical bundle that plugs the periplasmic end. Mutagenesis shows that specific extracellular loops are required for in vivo capsule assembly. The data show that Wzi binds the K30 carbohydrate polymer and, crucially, that mutants functionally deficient in vivo show no binding to K30 polymer in vitro. We conclude that Wzi is a novel outer-membrane lectin that assists in the formation of the bacterial capsule via direct interaction with capsular polysaccharides.
许多致病性细菌将自身包裹在多糖荚膜中，荚膜为细菌提供了抵御宿主物理和免疫挑战的屏障。荚膜在细菌周围组装的机制尚不清楚。Wzi 是大肠杆菌的一种完整的外膜蛋白，与 1 组荚膜的形成有关。Wzi 的 2.6Å 分辨率结构揭示了一种具有独特排列的 18 股 β-桶折叠结构，其具有阻止细胞外进入的新型长细胞外环排列和阻塞周质端的螺旋束。突变分析表明，特定的细胞外环是体内荚膜组装所必需的。这些数据表明，Wzi 结合了 K30 碳水化合物聚合物，至关重要的是，体内功能缺陷的突变体在体外与 K30 聚合物没有结合。我们得出结论，Wzi 是一种新型的外膜凝集素，通过与荚膜多糖的直接相互作用，协助细菌荚膜的形成。
