Shear-induced structural changes and denaturation of bovine immunoglobulin G and serum albumin at different temperatures

Abstract

Shearing can modify native properties of proteins alone or in combination with heating. Effects of shearing on secondary structure, extent of denaturation and interactions of immunoglobulin G (IgG) and bovine serum albumin (BSA) were studied at temperatures where these changes start to take place. Pure IgG (0.8 mL mL−1) or BSA (0.4 mg mL−1) and their binary mixture were subjected to selected temperature and time combinations (70, 72, 75 or 85 °C for 0–2 min or 20 °C for 20 min) without or with a constant shear at 1000 s−1. Shearing of pure IgG or BSA for 20 min at 20 °C resulted in protein denaturation (≥4%) and loss of secondary structure, mainly β-sheets in IgG and α-helices and β-turns in BSA. The shearing appeared to preserve native proteins to a varying degree when pure IgG and BSA were sheared at 72 °C and 75 °C for 0–2 min, respectively, in comparison to their non-sheared counterparts, possibly through a countereffect generated by shear against thermal effect. The shearing mostly induced denaturation of IgG and BSA under other conditions tested. The changes in the secondary structure largely coincided with protein denaturation or preservation results. The shearing had no apparent impact on aggregation of protein molecules due to covalent interactions in both, pure and binary, dispersions at 75 or 85 °C for 0–2 min. Heating at 85 °C for 2 min resulted in formation of covalently bound intra- and intermolecular aggregates in the pure and binary mixture, respectively, regardless of shearing.