Identification of two type IIa IgG-binding proteins expressed by a single group A streptococcus.

Functional heterogeneity associated with Ig-binding proteins expressed by group A streptococci is well documented. In this study we have demonstrated that treatment of group A streptococcal isolate 64/14 with CNBr resulted in the solubilization of two different sized proteins that displayed identical functional reactivity with human IgG1, IgG2, and IgG4 (characteristics of a type IIa binding protein). Monospecific polyclonal antibodies to each form of type IIa molecule were prepared and no antigenic cross-reactivity between the two m.w. forms of type IIa binding protein could be detected. The smaller m.w. protein was shown to be identical or closely related to the recombinant type IIa protein cloned from strain CS110. These studies provide further evidence for the heterogeneity of type II Ig-binding proteins expressed by pathogenic group A streptococci.