Apolipoprotein A-IMilano anion exchange chromatography: Mass transfer and adsorption kinetics

Purification of Therapeutic Antibodies by Protein A Affinity Chromatography

Protein A affinity chromatography is widely used for capturing therapeutic antibodies. It offers high binding capacity, selectivity, and resin reusability while delivering high yield and product purity. The Protein A step is ubiquitous in its presence in purification platforms for production of antibody products due to the effective clearance it offers of impurities, high and low molecular weight species (HMW and LMW), host cell proteins (HCP), and DNA. In this chapter, we describe a highly selective Protein A affinity chromatography protocol for purification of monoclonal antibodies.

Apolipoprotein A-I(Milano) anion exchange chromatography: Self association and adsorption equilibrium

The self-associative properties of apolipoprotein A-I(Milano) (apoA-I(M)) were investigated in relationship to its anion exchange behavior on Q-Sepharose-HP with and without the addition of urea as a denaturant. Self-association was dependent on protein and urea concentration and both influenced interactions of the protein with the chromatographic surface. In the absence of urea, apoA-I(M) was highly associated and existed primarily as a mixture of homodimer, tetramer and hexamer forms. Under these conditions, since the binding strength was greater for the oligomer forms, broad, asymmetrical peaks were obtained in both isocratic and gradient elution. Adding urea depressed self-association and caused unfolding. This resulted in sharper peaks but also decreased the binding strength. Thus, under these conditions chromatographic elution occurred at lower salt concentrations. The adsorption isotherms obtained at high protein loadings were also influenced by self-association and by the varying binding strength of the differently associated and unfolded forms. The isotherms were thus dependent on protein, urea, and salt concentration. Maximum binding capacity was obtained in the absence of urea, where adsorption of oligomers was shown to be dominant. Adding urea reduced the apparent binding capacity and weakened the apparent binding strength. A steric mass action model accounting for competitive binding of the multiple associated forms was used to successfully describe the equilibrium binding behavior using parameters determined from isocratic elution and isotherm experiments.