Institute of Molecular Biology & Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093, Zürich, Switzerland.
Nat Commun. 2019 Apr 5;10(1):1565. doi: 10.1038/s41467-019-09603-1.
Contractile injection systems (CISs) mediate cell-cell interactions by a phage tail-like apparatus. Their conserved mechanism relies on the anchoring of the proximal end of a sheath-tube module to a membrane, followed by contraction of the sheath towards the attachment site and ejection of the inner tube. Here we reveal a major variation of the CIS mechanism in the type six secretion system (T6SS) of enteroaggregative Escherichia coli (EAEC). We show that both ends of the sheath-tube module are attached to opposite sides of the cell, enabling the structure to contract in two opposite directions. The protein TssA1 mediates the interaction of the distal end with the cell envelope, the termination of tail elongation, and non-canonical contraction towards the distal end. We provide a framework for the molecular processes at the T6SS distal end. Further research will address whether bidirectional contraction allows for bidirectional effector secretion. The unrecognized concept of non-canonical contractions could be relevant to biofilms of the human intestine.
收缩注射系统 (CISs) 通过噬菌体尾状装置介导细胞间相互作用。它们保守的机制依赖于鞘管模块的近端锚定在膜上，然后鞘向附着位点收缩并喷射出内管。在这里，我们揭示了肠聚集性大肠杆菌 (EAEC) 中 6 型分泌系统 (T6SS) 中 CIS 机制的一个主要变化。我们表明，鞘管模块的两端都附着在细胞的相对侧，从而使结构能够向两个相反的方向收缩。蛋白 TssA1 介导了末端与细胞包膜的相互作用、尾部延伸的终止以及向末端的非规范收缩。我们为 T6SS 末端的分子过程提供了一个框架。进一步的研究将解决双向收缩是否允许双向效应物分泌。非规范收缩的未被识别的概念可能与人类肠道生物膜有关。
