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The major outer sheath protein forms distinct conformers and multimeric complexes in the outer membrane and periplasm

Robbins Puthenveetil1, Sanjiv Kumar2, Melissa J Caimano2,3,4

  • 1Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, CT, USA.

Scientific Reports
|October 18, 2017
PubMed

Insights

The major outer sheath protein (MOSP) in Treponema denticola forms distinct outer membrane and periplasmic trimers. These conformers interact with different partners, suggesting unique folding pathways for outer membrane targeting.

Area of Science:

  • Microbiology
  • Protein Biochemistry
  • Cell Biology

Background:

  • The major outer sheath protein (MOSP) is a key virulence factor in Treponema denticola (TDE), a bacterium with a complex cell envelope.
  • MOSP is predicted to have N-terminal (MOSP ) and C-terminal (MOSP ) domains, with MOSP exhibiting porin activity.

Purpose of the Study:

  • To investigate the structural conformations and cellular localization of MOSP in TDE.
  • To identify MOSP's interaction partners and elucidate its folding and transport pathways.
  • To compare MOSP processing in TDE with its processing in E. coli.

Main Methods:

  • Bioinformatics analysis of MOSP structure.
  • In vitro biophysical analysis of MOSP domains.
  • Immunofluorescence assays, surface proteolysis, and cell fractionation.
  • Mass spectrometry (MS) for protein interaction analysis.

Main Results:

  • MOSP forms amphiphilic trimers, while MOSP forms hydrophilic monomers.
  • In TDE, MOSP exists as both outer membrane (OM) and periplasmic trimers; in E. coli (PelB-MOSP), only OM trimers are formed.
  • OM-MOSP associates with dentilisin, oligopeptide-binding proteins (OBPs), and BamA, while periplasmic MOSP interacts with TDE1658.

Conclusions:

  • MOSP targeting to the TDE outer membrane likely utilizes the canonical BAM pathway.
  • The formation of a stable periplasmic MOSP conformer involves a unique export-related folding pathway not found in E. coli.
  • Differential protein interactions highlight distinct functional roles for MOSP conformers in TDE pathogenesis.

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