Immunoglobulin binding by the regular surface array of Aeromonas salmonicida.
The cell surface of Aeromonas salmonicida is covered by a regular surface array composed of a single species of protein, the A-protein (Phipps, B. M., Trust, T. J., Ishiguro, E. E., and Kay, W. W. (1983) Biochemistry 22, 2934-2939). The array, known as the A-layer, is the key virulence factor for this organism. Cells containing the A-layer specifically bound rabbit IgG and human IgM with high affinity (KD = 1.0 X 10(-6) M and 3.3 X 10(-6) M, respectively), but neither isogenic A-protein-deficient strains nor an Aeromonas hydrophila strain also possessing a regular surface array had binding activity. Selective removal of A-protein at pH 2.2 inactivated IgG binding. Structurally intact IgG was requisite for binding since both Fab and Fc fragments were inactive. Aeromonas A-protein did not share the same IgG binding sites as Staphylococcus aureus protein A. Purified A-protein bound IgG only weakly, but reassembled A-layer regained binding activity. Protein modification and perturbation of the A-layer indicated that no single amino acid residue was critical for binding, and that the binding site consisted of a native arrangement of at least four A-protein monomers in the layer.
Phipps
B M
BM
Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
Kay
W W
WW
D000333:Aeromonas / Q000276:immunology*; D001667:Binding, Competitive; D002462:Cell Membrane / Q000276:immunology; D007141:Immunoglobulin Fc Fragments / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism*; D007700:Kinetics; D011961:Receptors, Fc / Q000378:metabolism*; D017452:Receptors, IgG
D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D011961:Receptors, Fc; D017452:Receptors, IgG