Biozentrum, University of Basel, CH 4056 Basel, Switzerland; email:
Annu Rev Microbiol. 2019 Sep 8;73:621-638. doi: 10.1146/annurev-micro-020518-115420. Epub 2019 Jun 21.
Bacteria need to deliver large molecules out of the cytosol to the extracellular space or even across membranes of neighboring cells to influence their environment, prevent predation, defeat competitors, or communicate. A variety of protein-secretion systems have evolved to make this process highly regulated and efficient. The type VI secretion system (T6SS) is one of the largest dynamic assemblies in gram-negative bacteria and allows for delivery of toxins into both bacterial and eukaryotic cells. The recent progress in structural biology and live-cell imaging shows the T6SS as a long contractile sheath assembled around a rigid tube with associated toxins anchored to a cell envelope by a baseplate and membrane complex. Rapid sheath contraction releases a large amount of energy used to push the tube and toxins through the membranes of neighboring target cells. Because reach of the T6SS is limited, some bacteria dynamically regulate its subcellular localization to precisely aim at their targets and thus increase efficiency of toxin translocation.
细菌需要将大分子从细胞质输送到细胞外空间，甚至输送到相邻细胞的膜上，以影响其环境、防止捕食、击败竞争对手或进行交流。为了使这一过程高度调控和高效，多种蛋白质分泌系统已经进化出来。VI 型分泌系统（T6SS）是革兰氏阴性菌中最大的动态组装体之一，允许将毒素输送到细菌和真核细胞中。结构生物学和活细胞成像的最新进展表明，T6SS 是一个围绕刚性管组装的长收缩鞘，相关毒素通过基部和膜复合物锚定在细胞包膜上。鞘的快速收缩释放出大量能量，用于推动管和毒素穿过相邻靶细胞的膜。由于 T6SS 的作用范围有限，一些细菌会动态调节其亚细胞定位，以精确瞄准目标，从而提高毒素转位的效率。
