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A Visual Assay to Monitor T6SS-mediated Bacterial Competition
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A unique bacterial secretion machinery with multiple secretion centers.

Liqiang Song1, John D Perpich2, Chenggang Wu1

  • 1Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, TX 77030.

Proceedings of the National Academy of Sciences of the United States of America
|April 26, 2022
PubMed
Summary
This summary is machine-generated.

The Porphyromonas gingivalis type IX secretion system (T9SS), crucial for periodontal disease, forms a unique molecular machine. This system utilizes proton motive force to translocate virulence factors across the bacterial outer membrane.

Keywords:
cryoelectron tomographyporphyromonasprotein transportproton motive forcetype IX secretion

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Area of Science:

  • Microbiology
  • Structural Biology
  • Bacterial Pathogenesis

Background:

  • The type IX secretion system (T9SS) in Porphyromonas gingivalis is essential for secreting virulence factors like gingipains, contributing to periodontal disease.
  • Understanding the T9SS structure and mechanism is key to developing therapeutic strategies against this pathogen.

Purpose of the Study:

  • To elucidate the high-resolution structure and assembly of the Porphyromonas gingivalis type IX secretion system (T9SS).
  • To understand the functional mechanism of substrate translocation across the outer membrane.

Main Methods:

  • In situ cryoelectron tomography was employed to visualize the T9SS structure within P. gingivalis.
  • Analysis of protein-protein interactions and conformational changes of T9SS components.

Main Results:

  • The P. gingivalis T9SS comprises 18 PorM dimers forming a periplasmic ring, interacting with a PorKN ring complex near the outer membrane.
  • Proton motive force energizes PorMKN translocation complexes, indicating distinct activation states.
  • A 12-fold symmetric cytoplasmic complex involving PorM and PorL is required for assembly at the inner membrane.
  • Substrates are translocated across the outer membrane via eight Sov translocons arranged in a ring.

Conclusions:

  • The T9SS assembles as a unique supramolecular machine with distinct motor and export pore components.
  • This structural and mechanistic insight provides a foundation for targeting the T9SS in P. gingivalis infections.