Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA; Center for Phage Technology, Department of Biochemistry and Biophysics.
J Mol Biol. 2020 Jul 24;432(16):4623-4636. doi: 10.1016/j.jmb.2020.06.013. Epub 2020 Jun 17.
Optimal phage propagation depends on the regulation of the lysis of the infected host cell. In T4 phage infection, lysis occurs when the holin protein (T) forms lesions in the host membrane. However, the lethal function of T can be blocked by an antiholin (RI) during lysis inhibition (LIN). LIN sets if the infected cell undergoes superinfection, then the lysis is delayed until host/phage ratio becomes more favorable for the release of progeny. It has been thought that a signal derived from the superinfection is required to activate RI. Here we report structures that suggest a radically different model in which RI binds to T irrespective of superinfection, causing it to accumulate in a membrane as heterotetrameric 2RI-2T complex. Moreover, we show the complex binds non-specifically to DNA, suggesting that the gDNA from the superinfecting phage serves as the LIN signal and that stabilization of the complex by DNA binding is what defines LIN. Finally, we show that soluble domain of free RI crystallizes in a domain-swapped homotetramer, which likely works as a sink for RI molecules released from the RI-T complex to ensure efficient lysis. These results constitute the first structural basis and a new model not only for the historic LIN phenomenon but also for the temporal regulation of phage lysis in general.
噬菌体的最佳繁殖取决于受感染宿主细胞裂解的调控。在 T4 噬菌体感染中，当溶孔蛋白（T）在宿主膜上形成损伤时，就会发生裂解。然而，在裂解抑制（LIN）期间，抗溶孔蛋白（RI）可以阻断 T 的致死功能。如果感染的细胞发生超感染，那么裂解就会延迟，直到宿主/噬菌体的比例更有利于释放后代。人们一直认为，来自超感染的信号需要激活 RI。在这里，我们报告的结构表明了一个截然不同的模型，即 RI 与 T 结合，而不管是否发生超感染，导致其作为异四聚体 2RI-2T 复合物积累在膜中。此外，我们还表明该复合物可以非特异性地结合 DNA，这表明来自超感染噬菌体的 gDNA 是 LIN 信号，而 DNA 结合对复合物的稳定是定义 LIN 的原因。最后，我们表明游离 RI 的可溶性结构域在一个结构域交换的同源四聚体中结晶，这可能作为从 RI-T 复合物释放的 RI 分子的汇，以确保有效的裂解。这些结果不仅为历史悠久的 LIN 现象，而且为噬菌体裂解的时间调控提供了第一个结构基础和新模型。
