摘要

模块化细菌素是一类重要的分泌蛋白毒素，其活性范围窄，参与革兰氏阴性菌之间的干扰竞争。这些抗菌蛋白包括与靶细胞结合的结构域和羧基末端的毒素模块。生产者的自我抑制是通过共表达连接的免疫基因提供的，该基因通过形成细菌素-免疫复合物或通过插入内膜瞬时抑制毒素的活性，这取决于毒素模块的类型。我们证明了对PmnH的菌株特异性抑制活性，PmnH是一种具有前所未有的双毒素结构的假单胞菌细菌素，既含有大肠杆菌素M结构域，潜在地干扰肽聚糖的合成，又含有新的大肠杆菌素N型结构域，这是铜绿假单胞菌脓菌素S5中不同于大肠杆菌素Ia型结构域的成孔模块。下游连接的基因产物赋予易感菌株PmnH免疫力。蛋白ImnH，具有类似于假单胞菌大肠杆菌素M样和成孔免疫蛋白的跨膜拓扑结构，尽管与这两种蛋白基本上没有同源性。PmnH在铁限制生长条件下增强的杀伤活性反映了铁铬型转运蛋白进入靶细胞的寄生作用，此处显示的策略也可用于假单胞菌的单域大肠杆菌素M样细菌素。在细菌素基因中整合第二种毒素模块可以提供对抗细菌的竞争优势，所述细菌对两种毒素活性中的仅一种显示免疫。

Modular bacteriocins represent a major group of secreted protein toxins with a narrow spectrum of activity, involved in interference competition between Gram-negative bacteria. These antibacterial proteins include a domain for binding to the target cell and a toxin module at the carboxy terminus. Self-inhibition of producers is provided by coexpression of linked immunity genes that transiently inhibit the toxin’s activity through formation of bacteriocin-immunity complexes or by insertion in the inner membrane, depending on the type of toxin module. We demonstrate strain-specific inhibitory activity for PmnH, a Pseudomonasbacteriocin with an unprecedented dual-toxin architecture, hosting both a colicin M domain, potentially interfering with peptidoglycan synthesis, and a novel colicin N-type domain, a pore-forming module distinct from the colicin Ia-type domain inPseudomonas aeruginosa pyocin S5. A downstream-linked gene product confers PmnH immunity upon susceptible strains. This protein, ImnH, has a transmembrane topology similar to that of Pseudomonas colicin M-like and pore-forming immunity proteins, although homology with either of these is essentially absent. The enhanced killing activity of PmnH under iron-limited growth conditions reflects parasitism of the ferrichrome-type transporter for entry into target cells, a strategy shown here to be used as well by monodomain colicin M-like bacteriocins from pseudomonads. The integration of a second type of toxin module in a bacteriocin gene could offer a competitive advantage against bacteria displaying immunity against only one of both toxic activities.

http://mbio.asm.org/content/8/1/e01961-16.short