Wang I N, Smith D L, Young R
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128, USA.
Annu Rev Microbiol. 2000;54:799-825. doi: 10.1146/annurev.micro.54.1.799.
Two proteins, an endolysin and a holin, are essential for host lysis by bacteriophage. Endolysin is the term for muralytic enzymes that degrade the cell wall; endolysins accumulate in the cytosol fully folded during the vegetative cycle. Holins are small membrane proteins that accumulate in the membrane until, at a specific time that is "programmed" into the holin gene, the membrane suddenly becomes permeabilized to the fully folded endolysin. Destruction of the murein and bursting of the cell are immediate sequelae. Holins control the length of the infective cycle for lytic phages and so are subject to intense evolutionary pressure to achieve lysis at an optimal time. Holins are regulated by protein inhibitors of several different kinds. Holins constitute one of the most diverse functional groups, with >100 known or putative holin sequences, which form >30 ortholog groups.
两种蛋白质，即内溶素和穿孔素，对于噬菌体裂解宿主至关重要。内溶素是指降解细胞壁的溶壁酶；内溶素在营养周期中以完全折叠的形式积累在细胞质中。穿孔素是积累在膜上的小膜蛋白，直到在穿孔素基因中“编程”的特定时间，膜突然对完全折叠的内溶素变得通透。胞壁质的破坏和细胞破裂是直接后果。穿孔素控制裂解性噬菌体的感染周期长度，因此面临强大的进化压力，以便在最佳时间实现裂解。穿孔素受几种不同类型的蛋白质抑制剂调控。穿孔素构成最多样化的功能组之一，有超过100个已知或推定的穿孔素序列，形成超过30个直系同源组。
