Protein adsorption and separation with monomodal and multimodal anion exchange chromatography resins. Part II. Mechanisms of protein aggregation on the chromatographic surface

Abstract

BACKGROUND: Proteins on chromatographic surfaces can undergo conformational changes, leading to aggregate formation. Such effects have been reported previously for hydrophobic interaction and cation exchange chromatography. In Part I of this work, we examined protein adsorption behavior on monomodal (Nuvia HP-Q) and multimodal anion exchangers (Nuvia aPrime and Capto Adhere), observing that aggregates are also formed on these multimodal resins. In this work we examine the underlying mechanisms and the conditions that affect aggregate formation. RESULTS: Incubating the multimodal anion exchangers with pure bovine serum albumin monomer at low ionic strength results in the formation of dimer and higher-order oligomers (up to hexamers) to an extent that depends on the incubation time. The percentage of total protein initially bound that is desorbed decreased from >85% with a 5 min incubation to <40% with 24 h incubation at pH 7.0, indicating that additional irreversibly bound species are formed on the resin surface. Load buffers leading to stronger binding (higher pH and/or lower salt) and higher temperatures (32 °C) result in more extensive aggregation. Minimal aggregation occurs, instead, for Nuvia HP-Q. CONCLUSION: BSA oligomers are formed directly on the surface of the multimodal resins studied and are eluted as discrete species at increasing salt concentrations. Aggregate formation is promoted by the ligand hydrophobicity and affects the separation of monomer–dimer mixtures by frontal chromatography, as the ability of the dimer in the feed to displace the adsorbed protein is impaired by gradual conversion of the monomer to stronger bound species. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).