CHARACTERIZATION OF PROTEIN-G EXPRESSED BY HUMAN GROUP-C AND GROUP-G STREPTOCOCCI

Treatment of human group C and G streptococci with cyanogen bromide results in solubilization of surface protein G molecules. Strain to strain variation in the quantity, molecular weight, and functional activity of protein G extracted from representative group C and G isolates led to the identification of five structurally and functionally distinct forms of the protein. These forms included molecules containing: (i) 3 albumin and 3 IgG binding domains; (ii) 3 albumin and 2 IgG binding domains; (iii) 2 albumin and 2 IgG binding domains; (iv) 0 albumin and 3 IgG binding domains; and (v) 0 albumin and 2 IgG binding domains. Only a single form of protein G was expressed by each streptococcal isolate and this was found to be a stable characteristic for that strain.