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Purifying monoclonal antibodies with protein G
Before being applied in therapy, monoclonal antibodies need to be purified to a very high degree. Affinity chromatography is a separation technique commonly used by pharmaceutical companies to purify monoclonal antibodies, using proteins to bind specifically to the antibody of interest. One of these is protein G. Normally it is found attached to the cell wall of certain strains of Streptococci, which makes industrial production cumbersome and expensive. However, the company Amersham Pharmacia Biotech developed a recombinant protein G produced in the bacterium Escherichia coli. This recombinant protein lacks the region binding to albumin, thereby avoiding undesirable adsorption of albumin from the cell culture broth and resulting in a purer fraction of antibodies after affinity chromatography.