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Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones.

Shehryar Ahmad1,2, Kara K Tsang1,2, Kartik Sachar3

  • 1Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada.

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|December 15, 2020
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Summary

This study identifies the prePAAR motif in over 6000 bacterial Type VI secretion system (T6SS) effectors. Eag chaperones stabilize these effectors via transmembrane helical packing, enabling bacterial warfare.

Keywords:
Gram-negative bacteriainfectious diseaseinterbacterial competitionmicrobiologymolecular chaperonesprotein transporttype VI secretion systemx-ray crystallography

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Area of Science:

  • Microbiology
  • Bacterial cell biology
  • Protein secretion

Background:

  • Type VI secretion systems (T6SSs) are crucial for interbacterial antagonism.
  • Many T6SS effectors possess N-terminal transmembrane domains (TMDs) for target cell membrane translocation.
  • The prevalence and secretion mechanisms of TMD-containing T6SS effectors are largely unknown.

Purpose of the Study:

  • To investigate the distribution and secretion mechanisms of TMD-containing T6SS effectors.
  • To characterize the role of chaperones in the export of these effectors.
  • To elucidate the structural basis of effector-chaperone interactions.

Main Methods:

  • Bioinformatic analysis to identify conserved motifs and effector classes.
  • Structural biology (co-crystal structures) to determine complex formations.
  • Biochemical assays to investigate protein-protein interactions.

Main Results:

  • Discovery of the conserved prePAAR motif in over 6000 TMD-containing T6SS effectors, primarily in Proteobacteria.
  • Classification of effectors into two distinct classes based on TMD number.
  • Structural elucidation of Eag chaperone complexes with Class I and Class II effectors, revealing stabilization via mimicry of transmembrane helical packing.
  • Identification of prePAAR residues mediating interactions with VgrG spikes.

Conclusions:

  • Eag chaperones are essential for the export of two distinct families of T6SS membrane protein effectors.
  • Chaperone-TMD interactions stabilize effectors through mimicking transmembrane helical packing.
  • The prePAAR motif plays a dual role in effector stabilization and interaction with the T6SS apparatus.