Recombinant Protein A is an immunoglobulin-binding protein derived from the cell wall of the bacterium Staphylococcus aureus. It is composed of five homologous Ig-binding domains that fold into a three-helix bundle. Each domain is able to bind proteins from many of mammalian species, most notably IgGs. Protein A binds with high affinity to human IgG1 and IgG2 as well as mouse IgG2a and IgG2b. Protein A binds with moderate affinity to human IgM, IgA and IgE as well as to mouse IgG3 and IgG1. It does not react with human IgG3 or IgD, nor will it react to mouse IgM, IgA or IgE.
