The effect of fatty acids, ionic strength, and electric fields on the microscopic dynamics of BSA aggregates

Abstract

This paper presents the microscopic dynamics of the concentrated suspensions of bovine serum albumin (BSA) proteins and their aggregates by dynamic light scattering (DLS) experiments. The effects of fatty acids binding to BSA, as well as the ionic strength and weak electric field, are discussed for affecting the stability of BSA suspensions against calcium-induced aggregation. By variation of the ionic strength, in the absence of an external electric field, DLS experiments show that monomer–BSA interactions (in the essentially fatty acid-free case) are overall repulsive but that, nevertheless, aggregation occurs to some extent. Also, the diffusive properties of different types of BSA are explored under an applied low-AC electric field by means of in situ electric small-angle depolarized DLS experiments, which reveal a significant decrease of the translational BSA–monomer diffusion coefficient with increasing frequency, while the aggregates indicate orientational motion via rotation on applying an electric field. These observations are interpreted in terms of (localized) orientation interactions obtained as oscillations in the intermediate scattering correlation function, as well as the anomalous slower relaxations as resulting in effective (collective) dynamics between monomeric BSA and their protein aggregates.