García-Bayona Leonor, Guo Monica S, Laub Michael T
Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.
Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States.
Elife. 2017 Mar 21;6:e24869. doi: 10.7554/eLife.24869.
Most bacteria are in fierce competition with other species for limited nutrients. Some bacteria can kill nearby cells by secreting bacteriocins, a diverse group of proteinaceous antimicrobials. However, bacteriocins are typically freely diffusible, and so of little value to planktonic cells in aqueous environments. Here, we identify an atypical two-protein bacteriocin in the α-proteobacterium that is retained on the surface of producer cells where it mediates cell contact-dependent killing. The bacteriocin-like proteins CdzC and CdzD harbor glycine-zipper motifs, often found in amyloids, and CdzC forms large, insoluble aggregates on the surface of producer cells. These aggregates can drive contact-dependent killing of other organisms, or cells not producing the CdzI immunity protein. The Cdz system uses a type I secretion system and is unrelated to previously described contact-dependent inhibition systems. However, Cdz-like systems are found in many bacteria, suggesting that this form of contact-dependent inhibition is common.
大多数细菌为了获取有限的营养物质，正与其他物种展开激烈竞争。一些细菌能够通过分泌细菌素（一类多样的蛋白质抗菌剂）来杀死附近的细胞。然而，细菌素通常可自由扩散，因此对于水环境中的浮游细胞几乎没有价值。在此，我们在α-变形杆菌中鉴定出一种非典型的双蛋白细菌素，它保留在产生菌细胞的表面，在那里介导细胞接触依赖性杀伤。类细菌素蛋白CdzC和CdzD含有通常在淀粉样蛋白中发现的甘氨酸拉链基序，并且CdzC在产生菌细胞表面形成大的不溶性聚集体。这些聚集体能够驱动对其他生物体或不产生CdzI免疫蛋白的细胞的接触依赖性杀伤。Cdz系统使用I型分泌系统，并且与先前描述的接触依赖性抑制系统无关。然而，在许多细菌中发现了类似Cdz的系统，这表明这种形式的接触依赖性抑制很常见。
