Protein G, a cell surface protein of group G streptococci, is a Type III Fc receptor that binds to the Fc region of IgG by a non-immune mechanism similar to that of protein A from Staphylococcus aureus. This product contains three IgG binding domains, but its albumin-binding region has been removed. Additionally, His-tag and cysteine have been added to N- and C-termini, respectively, to facilitate purification and conjugation. This does not affect the protein's ability to bind to IgG.