Mounting, structure and autocleavage of a type VI secretion-associated Rhs polymorphic toxin

Nat Commun. 2021 Dec 1;12(1):6998. doi: 10.1038/s41467-021-27388-0.


Bacteria have evolved toxins to outcompete other bacteria or to hijack host cell pathways. One broad family of bacterial polymorphic toxins gathers multidomain proteins with a modular organization, comprising a C-terminal toxin domain fused to a N-terminal domain that adapts to the delivery apparatus. Polymorphic toxins include bacteriocins, contact-dependent growth inhibition systems, and specialized Hcp, VgrG, PAAR or Rhs Type VI secretion (T6SS) components. We recently described and characterized Tre23, a toxin domain fused to a T6SS-associated Rhs protein in Photorhabdus laumondii, Rhs1. Here, we show that Rhs1 forms a complex with the T6SS spike protein VgrG and the EagR chaperone. Using truncation derivatives and cross-linking mass spectrometry, we demonstrate that VgrG-EagR-Rhs1 complex formation requires the VgrG C-terminal β-helix and the Rhs1 N-terminal region. We then report the cryo-electron-microscopy structure of the Rhs1-EagR complex, demonstrating that the Rhs1 central region forms a β-barrel cage-like structure that encapsulates the C-terminal toxin domain, and provide evidence for processing of the Rhs1 protein through aspartyl autoproteolysis. We propose a model for Rhs1 loading on the T6SS, transport and delivery into the target cell.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological
  • Bacterial Proteins / chemistry
  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / classification
  • Bacterial Toxins / genetics
  • Bacterial Toxins / metabolism*
  • Bacteriocins / chemistry
  • Contact Inhibition
  • Cryoelectron Microscopy
  • Mass Spectrometry
  • Models, Molecular
  • Photorhabdus / genetics
  • Photorhabdus / metabolism*
  • Type VI Secretion Systems / chemistry*
  • Type VI Secretion Systems / genetics
  • Type VI Secretion Systems / metabolism


  • Bacterial Proteins
  • Bacterial Toxins
  • Bacteriocins
  • Type VI Secretion Systems

Supplementary concepts

  • Photorhabdus laumondii