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

Effects of negative and positive cooperative adsorption of proteins on hydrophobic interaction chromatography media

The adsorption behavior of the model proteins: alpha-Lactalbumin, Bovine Serum Albumin, Lysozyme, and a monoclonal antibody, in single component and in binary mixtures, was investigated on two different hydrophobic interaction chromatography resins using both static and dynamic methods. A kinetic model of the adsorption process was developed, which accounted for protein unfolding and intermolecular interactions in the adsorbed phase. The latter incorporated positive cooperative interactions, resulting from preferred and multilayer adsorption on the adsorbent surface, as well as negative cooperative interactions attributed to exclusion effects due to size exclusion and repulsion. Cooperative adsorption resulted in negative or positive deviations from the Langmuir model for both single and multicomponent isotherms. The model was used to assess possible contributions of different adsorption mechanisms of proteins and their structurally different forms to the overall adsorption pattern, as well as to simulate chromatographic band profiles under different loading conditions. For proteins with unstable structure, the overall adsorption isotherm was dominated by binding of unfolded species at low surface coverage and by positive cooperative adsorption at high surface coverage. Furthermore, regardless of structural stability, exclusion effects influenced strongly adsorption equilibrium, particularly at low surface coverages. In case of chromatographic elution, i.e. under dynamic conditions, unfolding, negative cooperative adsorption, and kinetic effects governed the retention behavior and determined peak shapes, whereas the effect of positive cooperative adsorption was negligible.

Downstream Processing Technologies/Capturing and Final Purification : Opportunities for Innovation, Change, and Improvement. A Review of Downstream Processing Developments in Protein Purification

Increased pressure on upstream processes to maximize productivity has been crowned with great success, although at the cost of shifting the bottleneck to purification. As drivers were economical, focus is on now on debottlenecking downstream processes as the main drivers of high manufacturing cost. Devising a holistically efficient and economical process remains a key challenge. Traditional and emerging protein purification strategies with particular emphasis on methodologies implemented for the production of recombinant proteins of biopharmaceutical importance are reviewed. The breadth of innovation is addressed, as well as the challenges the industry faces today, with an eye to remaining impartial, fair, and balanced. In addition, the scope encompasses both chromatographic and non-chromatographic separations directed at the purification of proteins, with a strong emphasis on antibodies. Complete solutions such as integrated USP/DSP strategies (i.e., continuous processing) are discussed as well as gains in data quantity and quality arising from automation and high-throughput screening (HTS). Best practices and advantages through design of experiments (DOE) to access a complex design space such as multi-modal chromatography are reviewed with an outlook on potential future trends. A discussion of single-use technology, its impact and opportunities for further growth, and the exciting developments in modeling and simulation of DSP rounds out the overview. Lastly, emerging trends such as 3D printing and nanotechnology are covered. Graphical Abstract Workflow of high-throughput screening, design of experiments, and high-throughput analytics to understand design space and design space boundaries quickly. (Reproduced with permission from Gregory Barker, Process Development, Bristol-Myers Squibb).

Retention Behavior of Polyethylene Glycol and Its Influence on Protein Elution on Hydrophobic Interaction Chromatography Media

The retention behavior of polyethylene glycol (PEG) on different types of hydrophobic interaction chromatography (HIC) resins containing butyl, octyl, and phenyl ligands was analyzed. An incomplete elution or splitting of the polymer peak into two parts was observed, where the first one was eluted at the dead time of the column, whereas the second one was strongly retained. The phenomenon was attributed to conformation changes of the polymer upon its adsorption on hydrophobic surface. The effect enhanced with increasing molecular weight of the polymer and hydrophobicity of the HIC media. Addition of PEG to the mobile phase reduced binding of proteins to HIC resins, which was demonstrated with two model systems: lysozyme (LYZ) and immunoglobulin G (IgG), and their mixtures. In case of LYZ, the presence of PEG caused reduction in the protein retention, whereas for IgG—a decrease in efficiency of the protein capture. The effect depended on the adsorption pattern of PEG; it was pronounced in the systems in which conformational changes of the polymer were suggested to occur.

Changes in solvent exposure reveal the kinetics and equilibria of adsorbed protein unfolding in hydrophobic interaction chromatography

Hydrogen exchange has been a useful technique for studying the conformational state of proteins, both in bulk solution and at interfaces, for several decades. Here, we propose a physically based model of simultaneous protein adsorption, unfolding and hydrogen exchange in HIC. An accompanying experimental protocol, utilizing mass spectrometry to quantify deuterium labeling, enables the determination of both the equilibrium partitioning between conformational states and pseudo-first order rate constants for folding and unfolding of adsorbed protein. Unlike chromatographic techniques, which rely on the interpretation of bulk phase behavior, this methodology utilizes the measurement of a molecular property (solvent exposure) and provides insight into the nature of the unfolded conformation in the adsorbed phase. Three model proteins of varying conformational stability, alpha-chymotrypsinogen A, beta-lactoglobulin B, and holo alpha-lactalbumin, are studied on Sepharose HIC resins possessing assorted ligand chemistries and densities. alpha-Chymotrypsinogen, conformationally the most stable protein in the set, exhibits no change in solvent exposure at all the conditions studied, even when isocratic pulse-response chromatography suggests nearly irreversible adsorption. Apparent unfolding energies of adsorbed beta-lactoglobulin B and holo alpha-lactalbumin range from -4 to 3 kJ/mol and are dependent on resin properties and salt concentration. Characteristic pseudo-first order rate constants for surface-induced unfolding are 0.2-0.9 min(-1). While poor protein recovery in HIC is often associated with irreversible unfolding, this study documents that non-eluting behavior can occur when surface unfolding is reversible or does not occur at all. Further, this hydrogen exchange technique can be used to assess the conformation of adsorbed protein under conditions where the protein is non-eluting and chromatographic methods are not applicable.

A new thermodynamic model describes the effects of ligand density and type, salt concentration and protein species in hydrophobic interaction chromatography

A new thermodynamic model is derived that describes both loading and pulse-response behavior of proteins in hydrophobic interaction chromatography (HIC). The model describes adsorption in terms of protein and solvent activities, and water displacement from hydrophobic interfaces, and distinguishes contributions from ligand density, ligand type and protein species. Experimental isocratic response and loading data for a set of globular proteins on Sepharose resins of various ligand types and densities are described by the model with a limited number of parameters. The model is explicit in ligand density and may provide insight into the sensitivity of protein retention to ligand density in HIC as well as the limited reproducibility of HIC data.