Protein G is a small globular cell surface protein that binds to the constant region of many species of immunoglobulin G. Protein G can be used to detect, quantify and purify IgG antibodies and antibody/antigen complexes. Recombinant Protein G contains only IgG binding domains. The albumin-binding domain as well as cell wall and cell membrane binding domains have been removed to ensure the maximum specific IgG binding capacity. The 6-His-tag on N-terminus can be used for affinity purification or protein G detection using anti-His-tag antibodies. Protein G binds to all IgG subclasses from human, mouse and rat species. It also binds to total IgG from guinea pig, rabbit, goat, cow, sheep, and horse.