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Phase-variable outer membrane proteins in Escherichia coli

P Owen1, M Meehan, H de Loughry-Doherty

  • 1Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Ireland.

FEMS Immunology and Medical Microbiology
|December 1, 1996
PubMed
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Antigen 43 (Ag43) is a phase-variable outer membrane protein in Escherichia coli that influences colony form and autoaggregation. Its expression is regulated by DNA methylation and OxyR, suggesting a role in bacterial adhesion and variation.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Pathogenesis

Background:

  • Escherichia coli outer membrane proteins exhibit phase variation, influencing bacterial behavior.
  • Antigen 43 (Ag43) is a key protein involved in colony morphology and autoaggregation.
  • Ag43 is composed of alpha 43 and beta 43 subunits, with alpha 43 potentially acting as an adhesin.

Purpose of the Study:

  • To investigate the structure, function, and regulation of the phase-variable Antigen 43 (Ag43) protein in Escherichia coli.
  • To elucidate the molecular mechanisms underlying Ag43 phase variation.
  • To explore the potential role of Ag43 and related proteins as adhesins.

Main Methods:

  • Analysis of Ag43 protein subunits (alpha 43 and beta 43) and their properties.

Related Experiment Videos

  • Investigation of Ag43 phase variation rates and regulation by DNA methylation (dam) and OxyR.
  • Sequence homology analysis of alpha 43 with known adhesins.
  • Detection and characterization of a related 94 kDa outer membrane protein.

    • Main Results:

    • Ag43 is a bipartite complex of alpha 43 and beta 43, with alpha 43 expressed on the surface.
    • Ag43 expression undergoes reversible phase variation, regulated by DNA methylation and OxyR.
    • Alpha 43 shares homology with enterobacterial adhesins and contains an RGD motif.
    • A related 94 kDa protein, potentially a precursor, exists in some E. coli strains.

    Conclusions:

    • Ag43 plays a significant role in E. coli colony variation and autoaggregation.
    • Phase variation of Ag43 is controlled by DNA methylation and OxyR, likely through transcriptional regulation.
    • Ag43 represents a potential adhesin and may belong to a family of related outer membrane proteins.
    • The findings suggest Ag43 and similar proteins are important for E. coli adaptation and pathogenesis.