Recombinant Protein A/G

Source : Escherichia coli. The recombinant Protein A/G consists of 7 IgG-binding domains EDABC-C2C3, which corresponds to the Protein A and G domains that are included in the recombinant sequence. The Protein A portion is from Staphylococcus aureus segments E, D, A, B and C. The Protein G portion is from Streptococcus segments C2 and C3. The fusion protein has a predicted molecular mass of 50.5 kDa. But it migrates with an apparent molecular mass of approximately 45kDa in SDS-PAGE. Recombinant Protein A/G fusion protein joins IgG binding domains of both Protein A and Protein G. Protein A/G includes four Fc binding domains from Protein A and two from Protein G, yielding a final mass of 50.4 kDa. The binding dependency to pH of Protein A/G lower than Protein A, but has the additive properties of Protein A and G together. Protein A/G binds to all subclasses of human IgG, making it helpful for purifying polyclonal or monoclonal IgG antibodies whose subclasses have not been identifieed. Protein A/G binds to IgA, IgE, IgM and IgD. Protein A/G binds to all subclasses of mouse IgG excluding mouse IgA, IgM or serum albumin. This permits Protein A/G to be used in purification and detection of mouse monoclonal IgG antibodies, with no interference from IgA, IgM and serum albumin. Mouse monoclonal antibodies normally have a stronger affinity to the chimeric Protein A/G than to either Protein A or Protein G. Protein A/G also has been used for purification of macaque IgG.