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PorV is an Outer Membrane Shuttle Protein for the Type IX Secretion System
Michelle D Glew1, Paul D Veith1, Dina Chen1
1Oral Health Cooperative Research Centre, Melbourne Dental School, Bio21 Institute, The University of Melbourne, Melbourne, Australia.
Scientific Reports
|August 20, 2017
Summary
Porphyromonas gingivalis uses the Type IX Secretion System (T9SS) to anchor virulence factors like gingipains to its outer membrane. The novel sortase PorU is crucial for this process, cleaving signals and attaching proteins to anionic lipopolysaccharide.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Protein Secretion
Background:
- Porphyromonas gingivalis is a key pathogen in chronic periodontitis.
- Gingipains are major virulence factors secreted via the Type IX Secretion System (T9SS).
- Secretion involves anchoring to the outer membrane via anionic lipopolysaccharide (A-LPS) modification by the PorU sortase.
Purpose of the Study:
- To elucidate the mechanism of T9SS substrate anchoring to the Porphyromonas gingivalis cell surface.
- To investigate the role of the PorU sortase and associated proteins in substrate modification and attachment.
Main Methods:
- Identification of protein complexes using techniques like size exclusion chromatography.
- Analysis of mutant strains (porU mutants, CTD cleavage mutants).
- Quantitative label-free proteomics to determine protein abundance ratios.
Main Results:
- A 440 kDa attachment complex (PorU:PorV:PorQ:PorZ) was identified in wild-type P. gingivalis.
- Sub-complexes (PorU:PorV, PorQ:PorZ) were observed in mutants, indicating PorV and PorQ mediate anchoring.
- Immature T9SS substrates accumulated in a PorV-bound form in porU and CTD cleavage mutants.
- Proteomics data suggest PorV acts as a shuttle protein for T9SS substrates.
Conclusions:
- PorU is essential for cleaving the C-terminal domain signal (CTD) and conjugating T9SS substrates to A-LPS.
- The PorV protein functions as a shuttle, delivering substrates to the PorU-mediated attachment complex.
- This mechanism is critical for the cell surface display of P. gingivalis virulence factors.
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