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Related Experiment Videos

Structure-function analysis of the Shigella virulence factor IpaB.

A Guichon1, D Hersh, M R Smith

  • 1The Skirball Institute and Department of Microbiology, New York University Medical Center, New York, New York 10016, USA.

Journal of Bacteriology
|February 7, 2001
PubMed
Summary

Shigella flexneri invasion plasmid antigen B (IpaB) is crucial for bacterial pathogenesis. Specific residues in IpaB mediate macrophage apoptosis by interacting with caspase-1 (Casp-1), but this binding alone is insufficient for cytotoxicity.

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Area of Science:

  • Microbiology
  • Cell Biology
  • Immunology

Background:

  • Shigella flexneri causes dysentery, an acute inflammatory colon disease.
  • Key pathogenic events include bacterial invasion, phagosomal escape, and macrophage apoptosis.
  • The Shigella virulence factor invasion plasmid antigen B (IpaB) is essential for these processes.

Purpose of the Study:

  • To correlate functional domains of IpaB with its role in Shigella pathogenesis.
  • To investigate the specific role of IpaB in the induction of macrophage apoptosis via caspase-1 (Casp-1) activation.

Main Methods:

  • Generation and analysis of various IpaB mutants.
  • Assessment of IpaB stability, structure, and function in bacterial invasion, phagosomal escape, and cytotoxicity assays.

Related Experiment Videos

  • Investigation of IpaB binding to Casp-1 and its effect on apoptosis induction.

    • Main Results:

    • The N-terminus of IpaB is required for stable expression.
    • A putative amphipathic alpha-helical domain is important for IpaB structure.
    • Ten residues in the amino terminus hydrophobic region are critical for invasion, phagosomal escape, and cytotoxicity.
    • A mutant with altered residues binds Casp-1 but is not cytotoxic, indicating binding is insufficient for apoptosis.

    Conclusions:

    • The N-terminal hydrophobic region of IpaB contains critical residues for virulence.
    • IpaB interaction with Casp-1 is necessary but not sufficient for triggering macrophage apoptosis.
    • Further steps beyond IpaB-Casp-1 association are involved in activating macrophage apoptosis during Shigella infection.