Cryo-EM Structure and Assembly of an Extracellular Contractile Injection System

• Published in: Cell Vol. 177; no. 2; pp. 370 - 383.e15
• Main Authors: Jiang, Feng, Li, Ningning, Wang, Xia, Cheng, Jiaxuan, Huang, Yaoguang, Yang, Yun, Yang, Jianguo, Cai, Bin, Wang, Yi-Ping, Jin, Qi, Gao, Ning
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 04.04.2019
• Subjects: assembly; Bacteriophage T4 - chemistry; bacteriophage-like; Cell Membrane - chemistry; contractile injection system; cryo-electron microscopy; Cryoelectron Microscopy - methods; Models, Molecular; Photorhabdus - chemistry; Photorhabdus - metabolism; Photorhabdus - ultrastructure; Photorhabdus asymbiotica; Protein Conformation; PVC; Type VI Secretion Systems - metabolism; assembly; Photorhabdus asymbiotica; bacteriophage-like; PVC; cryo-electron microscopy; contractile injection system
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2019.02.020

Contractile injection systems (CISs) are cell-puncturing nanodevices that share ancestry with contractile tail bacteriophages. Photorhabdus virulence cassette (PVC) represents one group of extracellular CISs that are present in both bacteria and archaea. Here, we report the cryo-EM structure of an intact PVC from P. asymbiotica. This over 10-MDa device resembles a simplified T4 phage tail, containing a hexagonal baseplate complex with six fibers and a capped 117-nanometer sheath-tube trunk. One distinct feature of the PVC is the presence of three variants for both tube and sheath proteins, indicating a functional specialization of them during evolution. The terminal hexameric cap docks onto the topmost layer of the inner tube and locks the outer sheath in pre-contraction state with six stretching arms. Our results on the PVC provide a framework for understanding the general mechanism of widespread CISs and pave the way for using them as delivery tools in biological or therapeutic applications. [Display omitted] •Cryo-EM structure of an intact extracellular contractile injection system (eCIS)•Six heterodimers of wedge proteins constitute the hexagonal baseplate•A hexameric cap terminates and stabilizes the eCIS with six stretching arms•An assembly model for the biogenesis of the eCIS is proposed Structures of a bacterial extracellular contractile injection system, the Photorhabdus virulence cassette (PVC), reveal its assembly pathway and unique features compared to other phage tail-like complexes