Recombinant Protein A

Protein A, similar to Protein G, is an immunoglobulin-binding protein expressed in group C and G Streptococcal bacteria but with different specificities. Protein A may be conjugated with various reporter molecules including fluorescent dyes (FITC), enzyme markers (peroxidase, alpha-galactosidase, alkaline phosphatase), biotin, and colloidal gold without affecting the antibody binding site on the molecule. Additionally, Protein A may be immobilized on a solid support such as agarose or acrylic beads for the purification of either polyclonal or monoclonal immunoglobulins. It is also routinely used for immunoprecipitation assays. Protein A is a cell wall component produced by several strains of Staphylococcus aureus that consists of a single polypeptide chain and contains little or no carbohydrate. The Protein A molecule contains four alpha igh-affinity (Ka =108/mole) binding sites capable of interacting with the Fc region from IgG of several species including human and rabbit. Optimal binding occurs at pH 8.2, although binding also exists between pH 7.0- 7.6.