Department of Biochemistry and Biophysics, 2128 TAMU, Texas A&M University, College Station, Texas 77843-2128, USA.
Protein Sci. 2010 Oct;19(10):1967-77. doi: 10.1002/pro.485.
Phage holins and endolysins have long been known to play key roles in lysis of the host cell, disrupting the cytoplasmic membrane and peptidoglycan (PG) layer, respectively. For phages of Gram-negative hosts, a third class of proteins, the spanins, are involved in disrupting the outer membrane (OM). Rz and Rz1, the components of the lambda spanin, are, respectively, a class II inner membrane protein and an OM lipoprotein, are thought to span the entire periplasm by virtue of C-terminal interactions of their soluble domains. Here, the periplasmic domains of Rz and Rz1 have been purified and shown to form dimeric and monomeric species, respectively, in solution. Circular dichroism analysis indicates that Rz has significant alpha-helical character, but much less than predicted, whereas Rz1, which is 25% proline, is unstructured. Mixture of the two proteins leads to complex formation and an increase in secondary structure, especially alpha-helical content. Moreover, transmission electron-microscopy reveals that Rz-Rz1 complexes form large rod-shaped structures which, although heterogeneous, exhibit periodicities that may reflect coiled-coil bundling as well as a long dimension that matches the width of the periplasm. A model is proposed suggesting that the formation of such bundles depends on the removal of the PG and underlies the Rz-Rz1 dependent disruption of the OM.
噬菌体 holin 和内溶素长期以来一直被认为在宿主细胞裂解中发挥关键作用，分别破坏细胞质膜和肽聚糖 (PG) 层。对于革兰氏阴性宿主的噬菌体，第三类蛋白质，即 spanin，参与破坏外膜 (OM)。lambda spanin 的组成部分 Rz 和 Rz1 分别是一种 II 类内膜蛋白和一种 OM 脂蛋白，据推测它们通过可溶性结构域的 C 末端相互作用跨越整个周质。在这里，Rz 和 Rz1 的周质结构域已被纯化，并在溶液中分别显示为二聚体和单体形式。圆二色性分析表明，Rz 具有显著的α-螺旋特征，但远低于预测值，而 Rz1 是 25%的脯氨酸，无结构。两种蛋白质的混合物导致复杂的形成和二级结构的增加，特别是α-螺旋含量的增加。此外，透射电子显微镜揭示了 Rz-Rz1 复合物形成大的棒状结构，尽管异质，但表现出周期性，可能反映了卷曲螺旋的捆绑以及与周质宽度相匹配的长尺寸。提出了一种模型，表明这种束的形成取决于 PG 的去除，并为 Rz-Rz1 依赖的 OM 破坏提供了基础。
