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Human IgM molecules that bind staphylococcal protein A contain VHIII H chains
E H Sasso1, G J Silverman, M Mannik
1Department of Medicine, University of Washington, Seattle 98195.
Journal of Immunology (Baltimore, Md. : 1950)
|April 15, 1989
Summary
Staphylococcal protein A (SPA) binds to the Fab region of certain antibodies. This study shows SPA binding is a specific marker for VHIII heavy chains in human IgM molecules.
Area of Science:
- Immunology
- Bacteriology
- Structural Biology
Background:
- Staphylococcal protein A (SPA) is a bacterial membrane protein with binding sites for Fc gamma and the Fab region of various immunoglobulin (Ig) isotypes.
- Understanding the structure-function relationship of Ig-SPA interactions is crucial for immunological research.
Purpose of the Study:
- To establish a structure-function correlation for the binding of immunoglobulin (Ig) Fab regions to Staphylococcal protein A (SPA).
- To determine if SPA binding can serve as a marker for specific immunoglobulin heavy chain variable (VH) subgroups in human IgM.
Main Methods:
- Binding of 24 isolated human monoclonal IgM proteins to SPA was quantified using a solid-phase radioimmunoassay (RIA).
- VH and V kappa subgroups of each IgM were identified through SDS-PAGE, transfer blotting, and detection with specific antisera against framework region peptides.
Main Results:
- SPA binding was observed in 10 out of 11 VHIII IgM samples, but not in any of the VHI or VHII IgM samples.
- Fractionation of polyclonal IgM on SPA-Sepharose CL4B demonstrated that VHIII molecules predominantly bound to SPA, while VHI and VHII subgroups did not.
Conclusions:
- SPA binding is identified as a functional marker for VHIII heavy chains in human IgM molecules.
- This finding provides a specific method for identifying VHIII IgM, with implications for understanding antibody diversity and function.