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Immunoglobulin binding by the regular surface array of Aeromonas salmonicida
1Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
The Journal of Biological Chemistry
|July 5, 1988
Summary
Aeromonas salmonicida's A-layer protein is crucial for virulence, specifically binding IgG and IgM. This binding requires the intact A-layer structure, not isolated A-protein, highlighting its role in bacterial defense mechanisms.
Area of Science:
- Microbiology
- Immunology
- Structural Biology
Background:
- Aeromonas salmonicida possesses a surface protein array, the A-layer, identified as a key virulence factor.
- The A-layer's specific function in host-pathogen interactions, particularly immune molecule binding, remains incompletely understood.
Purpose of the Study:
- To investigate the binding characteristics of the Aeromonas salmonicida A-layer to immunoglobulins.
- To determine the structural requirements for A-layer mediated immunoglobulin binding and its implications for virulence.
Main Methods:
- Utilized Aeromonas salmonicida strains with and without the A-layer for binding assays.
- Performed binding studies with purified immunoglobulins (IgG, IgM) and their fragments (Fab, Fc).
- Investigated the effect of pH, protein purification, reassembly, and chemical modification on A-layer binding activity.
Main Results:
- A-layer expressing cells exhibited specific high-affinity binding for rabbit IgG and human IgM.
- Binding was dependent on the intact A-layer structure, with isolated A-protein showing weak binding.
- IgG binding was abolished by A-protein removal at low pH and required structurally intact IgG molecules.
- The binding site involved a native arrangement of at least four A-protein monomers, distinct from Staphylococcus aureus protein A binding sites.
Conclusions:
- The A-layer of Aeromonas salmonicida functions as a specific receptor for host immunoglobulins, contributing to virulence.
- The structural integrity of the A-layer and the immunoglobulin molecule are essential for high-affinity binding.
- The A-layer's immunoglobulin-binding mechanism is unique and does not involve shared sites with other known bacterial immunoglobulin-binding proteins.