Five Homologous Repeats of the Protein G-Related Protein MIG Cooperate in Binding to Goat Immunoglobulin G

Protein MIG, from Streptococcus dysgalactiae, binds α₂-macroglobulin and immunoglobulin G (IgG). MIG-derived fusion proteins with one to five IgG-binding repeats differed up to 72,000-fold in avidity for goat IgG, indicating a considerable cooperativity of the repeats. Significant sequence variation in the IgG-binding repeats was recognized. Protein MIG interacted with goat IgG1 via both the Fc and Fab parts.