EVIDENCE FOR INDEPENDENT BINDING DOMAINS WITHIN A GROUP-A STREPTOCOCCAL TYPE IIO IGG-BINDING PROTEIN

The gene for a type IIo IgG-binding protein has previously been cloned and sequenced. The similar to 60 000 M(r) recombinant gene product bi nds all four human IgG subclasses and fibrinogen. Treatment of this re combinant protein with CNBr results in generation of a series of fragm ents. One fragment, an similar to 32 000 M(r) polypeptide, binds IgG(1 ), IgG(2), and IgG(4) but neither IgG(3) nor fibrinogen. N-terminal am ino sequencing of this fragment indicated that this was an internal fr agment of the protein starting at amino acid 186 of the mature protein . These findings provide evidence for two distinct domains for binding IgG1, IgG(2), and IgG(4) and binding IgG(3) within a single bacterial IgG-binding protein.