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A Visual Assay to Monitor T6SS-mediated Bacterial Competition
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Published on: March 20, 2013

Molecular basis of type VI secretion system effector loading.

Patricia Paracuellos1,2, Ambre Bexter1,2, Jonasz B Patkowski1,2

  • 1Centre for Bacterial Resistance Biology, Imperial College, London, UK.

Nature Microbiology
|May 27, 2026
PubMed
Summary

Researchers uncovered how bacterial Type VI secretion systems (T6SSs) load effector proteins using cryo-electron microscopy. This reveals a stepwise mechanism for delivering diverse payloads into target cells.

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Area of Science:

  • Microbiology
  • Structural Biology
  • Molecular Biology

Background:

  • Type VI secretion systems (T6SSs) are complex bacterial nanomachines.
  • The mechanism of effector cargo loading into T6SS Hcp ring assemblies is not well understood.
  • Pseudomonas aeruginosa utilizes four distinct T6SSs, each with a unique Hcp protein.

Purpose of the Study:

  • To elucidate the structural basis of effector recruitment and loading into T6SS Hcp rings.
  • To investigate the interaction between the Tce1 effector and the Hcp3 ring from the P. aeruginosa H3-T6SS.
  • To propose a general mechanism for T6SS effector loading.

Main Methods:

  • Cryo-electron microscopy was employed to determine the structure of Tce1 cargo within Hcp3 rings.
  • Structural modeling was used to infer interactions for other effectors like Tce2.
  • Biochemical and biophysical techniques were utilized to analyze protein interactions.

Main Results:

  • The structure reveals a single Tce1 monomer interacting asymmetrically with, and enclosed by, two hexameric Hcp3 rings.
  • Key residues on the inner surface of the Hcp3 disc mediate effector binding.
  • A stepwise loading mechanism involving an initial Hcp-cargo complex followed by ring encapsulation was identified.
  • Structural modeling suggests conserved interactions for other effectors, including the antifungal Tce2.

Conclusions:

  • The study reveals a novel mechanism for effector loading into T6SS Hcp rings, involving asymmetric interactions and stepwise assembly.
  • This mechanism facilitates the coordinated delivery of a diverse range of effector payloads by T6SSs.
  • The findings provide insights into the molecular mechanisms underlying bacterial protein secretion and inter-bacterial interactions.