Gründling A, Manson M D, Young R
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA.
Proc Natl Acad Sci U S A. 2001 Jul 31;98(16):9348-52. doi: 10.1073/pnas.151247598. Epub 2001 Jul 17.
Holins comprise the most diverse functional group of proteins known. They are small bacteriophage-encoded proteins that accumulate during the period of late-protein synthesis after infection and cause lysis of the host cell at a precise genetically programmed time. It is unknown how holins achieve temporal precision, but a conserved feature of their function is that energy poisons subvert the normal scheduling mechanism and instantly trigger membrane disruption. On this basis, timing has been proposed to involve a progressive decrease in the energized state of the membrane until a critical triggering level is reached. Here, we report that membrane integrity is not compromised after the induction of holin synthesis until seconds before lysis. The proton motive force was monitored by the rotation of individual cells tethered by a single flagellum. The results suggest an alternative explanation for the lysis "clock," in which holin concentrations build to a critical level that leads to formation of an oligomeric complex that disrupts the membrane.
穿孔素是已知功能最为多样的蛋白质组。它们是由噬菌体编码的小蛋白，在感染后的晚期蛋白质合成阶段积累，并在精确的基因编程时间导致宿主细胞裂解。目前尚不清楚穿孔素如何实现时间上的精确性，但它们功能的一个保守特征是能量毒物会破坏正常的调度机制并立即引发膜破裂。在此基础上，有人提出时间控制涉及膜的能量化状态逐渐降低，直到达到临界触发水平。在这里，我们报告在穿孔素合成诱导后直到裂解前几秒，膜完整性并未受到损害。通过单个鞭毛固定的单个细胞的旋转来监测质子动力势。结果为裂解“时钟”提出了另一种解释，即穿孔素浓度积累到临界水平，导致形成破坏膜的寡聚复合物。
