Structural characterization of an extracellular contractile injection system from Photorhabdus luminescens in extended and contracted states.

Contractile injection systems (CISs) are phage-tail-like nanosyringes that mediate bacterial interactions by puncturing target cell membranes. Within these systems, Photorhabdus Virulence Cassettes (PVCs) can translocate toxins across eukaryotic target cell membranes. The structure of a PVC has been described at atomic level and engineered to deliver diverse protein cargoes into non-natively-targeted organisms. Despite the structural insights into several CISs, information on PVCs from other species and details on the contraction mechanism remain limited. Here, we present the single-particle cryo-electron microscopy structure of PlPVC1, a PVC from the nematode symbiont and insect pathogen Photorhabdus luminescens DJC, in both extended and contracted states. Our structure displays distinct structural features that differ from other CISs, such as a cage surrounding the central spike, a larger sheath adaptor, and a plug exposed to the tube lumen. Moreover, we present the structures of the PlPVC1 fiber as well as the baseplate of the contracted particle, yielding insight into the contraction mechanism. This study provides structural details of the contracted state of the PlPVC1 particle and supports the model in which contraction is triggered. Furthermore, it facilitates the comparison of PlPVC1 with other contractile systems and expands the scope of engineering opportunities for future biomedical and biotechnological applications.