Human IgM molecules that bind staphylococcal protein A contain VHIII H chains.
Staphylococcal protein A (SPA) is a bacterial membrane protein which has distinct binding sites for Fc gamma and for the Fab region of some IgM, IgG, IgA, and IgE molecules. This study establishes a structure-function correlation responsible for the binding of Ig Fab regions to SPA. Binding of 24 isolated human monoclonal IgM proteins to SPA was measured in a solid phase RIA. VH and V kappa subgroups of each IgM were determined by SDS-PAGE, transfer blotting, and detection with antisera prepared against specific first framework region peptides. Binding to SPA was seen with 10 of 11 VHIII IgM, but none of the 7 VHI or 6 VHII. Similarly, polyclonal IgM fractionated on a SPA-Sepharose CL4B column showed nearly complete partition of VHIII molecules into the SPA-binding fraction, and VHI and VHII subgroup proteins into the fall-through. We conclude that SPA binding is a functional marker for VHIII H chains in human IgM molecules.
Sasso
E H
EH
Department of Medicine, University of Washington, Seattle 98195.
Silverman
G J
GJ
Mannik
M
M
D001665:Binding Sites; D005803:Genes, Immunoglobulin; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000378:metabolism*; D007075:Immunoglobulin M / Q000378:metabolism*; D007135:Immunoglobulin Variable Region / Q000378:metabolism*; D013205:Staphylococcal Protein A / Q000378:metabolism*
D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region; D013205:Staphylococcal Protein A