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Regulation of type III secretion hierarchy of translocators and effectors in attaching and effacing bacterial

Wanyin Deng1, Yuling Li, Philip R Hardwidge

  • 1Michael Smith Laboratories, University of British Columbia, 301-2185, East Mall, Vancouver, British Columbia V6T 1Z4, Canada.

Infection and Immunity
|March 24, 2005
PubMed

Insights

SepL and SepD proteins in attaching and effacing (A/E) pathogens like EHEC and EPEC control the secretion of bacterial translocators and effectors. These proteins act as a molecular switch, responding to environmental signals like low calcium.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Pathogenesis

Background:

  • Attaching and effacing (A/E) bacterial pathogens, including enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and Citrobacter rodentium (CR), utilize a type III secretion system encoded by the locus of enterocyte effacement (LEE) pathogenicity island.
  • This system is crucial for translocating effector proteins into host cells, a key mechanism for pathogenesis.

Purpose of the Study:

  • To investigate the role of LEE-encoded proteins SepL and SepD in regulating type III secretion in A/E pathogens.
  • To determine if SepL and SepD function as a molecular switch controlling the secretion of translocators and effectors.
  • To explore the influence of environmental conditions, specifically calcium concentration, on this regulatory mechanism.

Main Methods:

  • Construction and analysis of sepL and sepD mutants in EHEC and EPEC.
  • Assessment of type III secretion profiles (translocators and effectors) in wild-type and mutant strains under various culture conditions.
  • Co-immunoprecipitation assays to confirm SepL and SepD interaction.
  • Cellular localization studies to determine the membrane association of SepL and SepD.

Main Results:

  • Mutations in sepL and sepD abolished translocator secretion while enhancing effector secretion in EHEC and EPEC.
  • SepL and SepD were shown to interact with each other and localize to bacterial membranes.
  • Low calcium concentrations in culture media mimicked the secretion profile of sepL/sepD mutants, inhibiting translocator secretion and promoting effector secretion.
  • The secretion profiles of sepL and sepD mutants were unaffected by changes in calcium concentration, indicating their central role in this environmental response.

Conclusions:

  • SepL and SepD are essential for efficient translocator secretion in A/E pathogens.
  • These proteins act as a critical molecular switch, mediating the transition from translocator to effector secretion.
  • SepL and SepD likely sense environmental cues, such as low calcium levels, to modulate type III secretion and bacterial virulence.

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