Protein instability during HIC: Evidence of unfolding reversibility,and apparent adsorption strength of disulfide bond‐reduced α‐lactalbumin variants

A two‐conformation, four‐state model has been proposed to describe protein adsorption and unfolding behavior on hydrophobic interaction chromatography (HIC) resins. In this work, we build upon previous study and application of a four‐state model to the effect of salt concentration on the adsorption and unfolding of the model protein α‐lactalbumin in HIC. Contributions to the apparent adsorption strength of the wild‐type protein from native and unfolded conformations, obtained using a deuterium labeling technique, reveal the free energy change and kinetics of unfolding on the resin, and demonstrate that surface unfolding is reversible. Additionally, variants of α‐lactalbumin in which one of the disulfide bonds is reduced were synthesized to examine the effects of conformational stability on apparent retention. Below the melting temperatures of the wild‐type protein and variants, reduction of a single disulfide bond significantly increases the apparent adsorption strength (～6–8 kJ/mol) due to increased instability of the protein. Finally, the four‐state model is used to accurately predict the apparent adsorption strength of a disulfide bond‐reduced variant. Biotechnol. Bioeng. 2009;102: 1416–1427. © 2008 Wiley Periodicals, Inc.