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High Resolution Electron Microscopy of the Helicobacter pylori Cag Type IV Secretion System Pili Produced in Varying Conditions of Iron Availability
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High Resolution Electron Microscopy of the Helicobacter pylori Cag Type IV Secretion System Pili Produced in Varying Conditions of Iron Availability

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Structural characterization of CFA/III and Longus type IVb pili from enterotoxigenic Escherichia coli

Subramaniapillai Kolappan1, Justin Roos, Alex S W Yuen

  • 1Molecular Biology and Biochemistry Department, Simon Fraser University, Burnaby, BC, Canada.

Journal of Bacteriology
|March 27, 2012
PubMed

Insights

Type IVb pili, CFA/III, mediate enterotoxigenic Escherichia coli aggregation. Structural analysis of the CFA/III pilin CofA reveals unique features and suggests high specificity in type IVb pilus assembly systems.

Area of Science:

  • Microbiology
  • Structural Biology
  • Bacterial Pathogenesis

Background:

  • Type IV pili are crucial virulence factors in Gram-negative bacteria, facilitating adhesion, motility, and microcolony formation.
  • Enterotoxigenic Escherichia coli (ETEC) utilizes type IVb pili, such as CFA/III and Longus, for pathogenesis.

Purpose of the Study:

  • To investigate the role of CFA/III pili in ETEC aggregation.
  • To determine the structure of CofA, the major pilin subunit of CFA/III.
  • To explore the specificity of the type IVb pilus assembly machinery.

Main Methods:

  • Crystallography to determine the 1.26-Å resolution structure of CofA.
  • Homology modeling for the Longus LngA pilin.
  • Computational modeling of the CFA/III pilus filament.
  • Heterologous expression of CofA in Vibrio cholerae.

Main Results:

  • A direct correlation was observed between CFA/III expression and ETEC aggregation.
  • CofA structure is similar to TcpA but features a unique 10-amino-acid insertion forming a 3(10)-helix.
  • The CFA/III pilus model reveals the insert fits into inter-subunit gaps, creating a smoother, more negatively charged filament than TCP.
  • Heterologous expression of CofA in V. cholerae did not result in CFA/III filament formation.

Conclusions:

  • CFA/III pili contribute to ETEC aggregation and microcolony formation.
  • The unique structural insert in CofA influences pilus filament properties.
  • Type IVb pilus assembly systems exhibit high specificity for their cognate pilin subunits.

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