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Protein G: a powerful tool for binding and detection of monoclonal and polyclonal antibodies.
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1985
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ImmunologyGlycobiologyAntigen ProcessingPolyclonal AntibodiesProtein GImmunoassaysImmunochemistryAntibody EngineeringProteomicsG Protein-coupled ReceptorPowerful ToolAntibody ScreeningCell BiologyClinical MicrobiologyRat Monoclonal AntibodyAntibody BiologyPathogenesisImmunoglobulin EMicrobiologyRadioactivity BoundMedicine
Protein G is a bacterial IgG‑binding protein isolated from group G streptococci. The study examined protein G’s avidity for various IgG subclasses and compared it to protein A. The authors quantified binding by mixing radiolabeled Ig with Sepharose‑coupled protein G or A and measured bound radioactivity, then applied iodine‑labeled protein G in Western blots to detect IgG antibodies. Protein G exhibited higher avidity than protein A for all tested IgG, binding all monoclonal IgG subclasses from mouse and rat, as well as polyclonal IgG from several mammals but not chicken, and proved effective for detecting IgG in Western blot assays.
Protein G is an immunoglobulin (IgG)-binding bacterial cell wall protein recently isolated from group G streptococci. We have investigated the avidity of protein G for various monoclonal and polyclonal Ig of the IgG class, and compared it with the binding properties of protein A, the staphylococcal Fc-binding protein. Radiolabeled Ig were mixed with Sepharose-coupled protein G or protein A, and the amounts of radioactivity bound to the matrix-coupled bacterial proteins were determined. The avidity was found to be greater for protein G than for protein A for all examined Ig. Protein G bound all tested monoclonal IgG from mouse IgG1, IgG2a, and IgG3, and rat IgG2a, IgG2b, and IgG2c. In addition, polyclonal IgG from man, cow, rabbit, goat, rat, and mouse bound to protein G, whereas chicken IgG did not. The binding property of protein G was additionally exploited in the Western blot assay, in which iodine-labeled protein G was used successfully for the detection of a rat monoclonal antibody against ovalbumin, and for the detection of rabbit and goat polyclonal whole antisera against human urinary proteins. In these experimental situations, protein G was found to be a powerful reagent for the detection of IgG, and consequently the antigen against which these antibodies are directed.