IDENTIFICATION OF 2 FUNCTIONAL FORMS OF IMMUNOGLOBULIN G3-BINDING PROTEIN EXPRESSED BY GROUP-A STREPTOCOCCI

Analysis of group A streptococcal immunoglobulin G (IgG)-binding prote in reactivity with different human IgG3-myeloma proteins provided evid ence for at least two functional forms of these molecules. Representat ive IgG3-binding molecules were isolated, bitinylated, and used as tra cers in competitive binding assays. Cross-inhibition studies demonstra ted the existence of two distinct patterns of IgG3-binding activity. P roteins of one form could be inhibited from binding to an IgG3-myeloma protein by streptococcal protein G while binding of the second form w as not inhibited. These studies further underscore the extent of heter ogeneity among immunoglobulin-binding proteins expressed by group A st reptococci.