Protein A

Protein A Chromatography relies on the specific and reversible binding of antibodies to an immobilized protein A ligand. Protein A is a 56 kDa surface protein native to the cell wall of the bacterium Staphylococcus aureus. It is composed of five immunoglobulin-binding domains, each of which are able to bind proteins from many mammalian species, most notably Immunoglobulin G (IgG) through the heavy chain within the Fc region. While the native form of Protein A was used as the ligand for first generation Protein A resins, the recombinant form (rProtein A) produced in E. coli is the most prevalent today. Modifications to the protein structure of the ligand, the advent of ligands composed of single domain multimers, and multipoint attachment have given rise to the caustic stable, high capacity and extremely robust Protein A resins in use today.

Applications
Protein A resins are the most frequently used affinity resins in biomanufacturing. Protein A chromatography is a very robust purification procedure and is used as a capture step due to its specificity. Today Protein A chromatography is the standard technique for capturing recombinant monoclonal antibodies. Depending on the intended use for the target molecule (antibodies for diagnostic testing) Protein A capturing might be the only chromatographic step required to achieve adequate product purity.​