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. It contains 3 IgG binding domains and is engineered to delete albumin-binding region. HRP has been covalently coupled to Protein G to produce the HRP-Protein G, which can be used in detection systems such as immunoblotting, ELISA, immunoperoxidase electron microscopy and immunohistochemistry.