抗生素的发现和应用是20世纪最伟大的成就。然而随着抗生素的使用，一些问题的出现限制了它们的应用。因此，人们急需开发新型的抗菌药物应用到临床和生产生活中。细菌素的许多优点表明他们是潜在的抗生素替代物，这包括它们的体内外活性高、毒性低和可利用益生菌产生等。细菌素是由细菌核糖体产生的一类短肽，对其它细菌有抑菌作用，但细菌素的产生菌株内有特定的免疫机制应对自身所产生的细菌素。单增李斯特菌是一类难以防治的食源性致病菌，而片球菌素样细菌素（PLBs）具有很强的杀伤单增李斯特菌的活性。目前由于人们对于细菌素的作用机制和免疫机制的不了解限制了它们的应用。有研究认为PLBs通过在靶细胞膜上形成孔洞来发挥杀伤作用，而且它们的活性发挥与靶细胞膜表面的甘露糖转运复合体（Man-PTS）密切相关。但关于Man-PTS在这个过程中发挥的作用一直不清楚。在本文的研究中，我们解析了单核细胞增生李斯特菌甘露糖转运复合体Man-PTS和及其与片球菌素结合的复合物的冷冻电子显微镜结构，分辨率分别为3.12?和2.45?。片球菌素PA-1是第一个也是最广泛研究的片球菌素样细菌素。结构显示，片球菌素PA-1的结合打开了Man-PTS的核心结构域，使其远离Vmotif结构域，在靶细胞的细胞质膜上形成孔。这是首次证明的可以通过诱导受体构象变化从而在受体内部形成通道的细菌素。在这一过程中，片球菌素PA-1的N-末端β-折叠区可以特异性地附着到Man-PTS核心结构域的细胞外表面，而C-末端的部分穿透膜并像楔子一样使Man-PTS裂开。细菌素产生菌内会产生一种免疫蛋白，保护自己不被自己的细菌素杀死。在本研究中，我们报道了来自清酒乳杆菌的细菌素受体-清酒乳杆菌素A-免疫蛋白的三元复合物的2.15 ?高分辨率冷冻电子显微镜结构。复合物结构显示，清酒乳杆菌素A与片球菌素PA-1结合在Man-PTS核心结构域的同一位置，而细菌素的C端螺旋尾部决定了核心结构域相对于Vmotif结构域的裂开程度，这种裂开直接导致了孔洞的形成。随着胞外侧细菌素的攻击，Man-PTS暴露其胞质侧结合面，以识别免疫蛋白的N端的四螺旋束。然后免疫蛋白的C末端环插入细菌素形成的孔洞中，阻止细菌素引起的渗漏。本文阐明了PLBs的作用机制和免疫机制，对于设计新型细菌素和对抗抗生素耐药的病原菌具有重要意义。本文解决了关于PLBs的若干问题，在该领域做出了重要贡献。
It is known that antibiotic therapy represents the most significant scientific achievement of the twentieth century. Unfortunately, several problems have arisen that limit these initial benefits. As a consequence, there is an urgent need for development of new antimicrobials that can be used in clinical settings and production.Bacteriocins have many properties which suggest that they are viable alternatives to antibiotics. These include their potency (as determined in vitro and in vivo), their low toxicity and the possibility of in situ production by probiotics.These are small, bacterially produced, ribosomally synthesized peptides that are active against other bacteria and against which the producer has a specific immunity mechanism to deal with the bacteriocin produced by itself. Listeria monocytogenes is a kind of foodborne pathogen that is difficult to control, and pediocin-like bacteriocins (PLBs) have strong activity against Listeria monocytogenes. But we have poor understanding of their action mechanism and immunity mechanism, which limits their application. Some studies have shown that pediocin-like bacteriocins kill bacteria by forming a pore in the target cell membrane, and their activity is closely related to the mannose phosphotransferase system (Man-PTS) on the surface of the target membrane. However, there has been controversy about the role of Man-PTS in this process.In this study, we report the cryo-electron microscopy structures of Man-PTS from Listeria monocytogenes alone and its complex with pediocin PA-1 at a resolution of 3.12 ? and 2.45 ?, respectively. Pediocin PA-1 is the first and most extensively studied representative pediocin-like bacteriocins. The complex structure revealed that the binding of pediocin PA-1 opens the Core domain of Man-PTS away from its Vmotif domain, creating a pore through the cytoplasmic membranes of target cells. This is the first bacteriocin proved to induce a conformational change in the receptor to lead to an irreversible opening of an intrinsic channel. During this process, the N-terminal β-sheet region of pediocin PA-1 can specifically attach to the extracellular surface of the Man-PTS Core domain, whereas the C-terminal half penetrates the membrane and cracks the Man-PTS like a wedge. The bacteriocin producers produce a cognate immunity protein that protects themselves from being killed by their own bacteriocin. In this study, we report the cryo-electron microscopy structure of the bacteriocin-receptor-immunity ternary complex from Lactobacillus sakei. The complex structure revealed that the PLBs bind to the same position on the Core domain of Man-PTS, while the C-terminal helical tail of bacteriocins determine the open range of the Core domain against the Vmotif domain for the transmembrane pore formation. With the attack of bacteriocins from the extracellular side, Man-PTS exposes its cytosolic binding surface for the recognition of the N-terminal four-helix bundle of the immunity protein. Then the C-terminal loop of the immunity protein inserts into the pore and blocks the leakage caused by bacteriocins. The elucidation of the toxicity and immunity mechanism of the PLBs bacteriocins was helpful to designing novel bacteriocins against the antibiotic-resistant pathogenic bacteria. This paper has solved several problems about PLBs and it has a significant influence in this field.
