Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, USA.
J Bacteriol. 2012 Oct;194(20):5667-74. doi: 10.1128/JB.01245-12. Epub 2012 Aug 17.
Phage lysis is a ubiquitous biological process, the most frequent cytocidal event in the biosphere. Lysis of Gram-negative hosts has been shown to require holins and endolysins, which attack the cytoplasmic membrane and peptidoglycan, respectively. Recently, a third class of lysis proteins, the spanins, was identified. The first spanins to be characterized were λ Rz and Rz1, an integral cytoplasmic membrane protein and an outer membrane lipoprotein, respectively. Previous work has shown that Rz and Rz1 form complexes that span the entire periplasm. Phase-contrast video microscopy was used to record the morphological changes involved in the lysis of induced λ lysogens carrying prophages with either the λ canonical holin-endolysin system or the phage 21 pinholin-signal anchor release (SAR) endolysin system. In the former, rod morphology persisted until the instant of an explosive polar rupture, immediately emptying the cell of its contents. In contrast, in pinholin-SAR endolysin lysis, the cell began to shorten and thicken uniformly, with the resultant rounded cell finally bursting. In both cases, lysis failed to occur in inductions of isogenic prophages carrying null mutations in the spanin genes. In both systems, instead of an envelope rupture, the induced cells were converted from a rod shape to a spherical form. A functional GFPΦRz chimera was shown to exhibit a punctate distribution when coexpressed with Rz1, despite the absence of endolysin function. A model is proposed in which the spanins carry out the essential step of disrupting the outer membrane, in a manner regulated by the state of the peptidoglycan layer.
噬菌体裂解是一种普遍存在的生物学过程，是生物圈中最常见的细胞杀伤事件。已经证明，革兰氏阴性宿主的裂解需要 holin 和内溶素，它们分别攻击细胞质膜和肽聚糖。最近，发现了第三类裂解蛋白，即 spanin。首先被表征的 spanin 是 λ Rz 和 Rz1，它们分别是一种完整的细胞质膜蛋白和一种外膜脂蛋白。先前的工作表明，Rz 和 Rz1 形成复合物，跨越整个周质。相差显微镜视频用于记录携带带有 λ 经典 holin-内溶素系统或噬菌体 21 穿孔素信号锚释放 (SAR) 内溶素系统的前噬菌体的诱导 λ 溶源菌裂解所涉及的形态变化。在前一种情况下，杆状形态一直持续到瞬间爆发性极破裂，立即将细胞内容物排空。相比之下，在穿孔素-SAR 内溶素裂解中，细胞开始均匀缩短和变厚，最终形成圆形细胞破裂。在这两种情况下，在携带 spanin 基因缺失突变的同基因前噬菌体的诱导中，裂解都没有发生。在这两种系统中，诱导细胞没有发生包膜破裂，而是从杆状形状转变为球形。尽管缺乏内溶素功能，但功能性 GFPΦRz 嵌合体与 Rz1 共表达时显示出点状分布。提出了一种模型，其中 spanin 执行破坏外膜的基本步骤，其方式受肽聚糖层状态的调节。
