Reversibility of Structural Rearrangements in Bovine Serum Albumin during Homomolecular Exchange from AgI Particles

Abstract

The reversibility of the homomolecular exchange of bovine serum albumin (BSA) from AgI particles was studied by differential scanning calorimetry, the binding of 8-anilino-1-naphthaIene-sulfonic acid, and circular dichroism spectroscopy. The structure of BSA in solution before adsorption, in the adsorbed state, and in solution after exchange was analyzed. To investigate the influence of electrostatics and surface crowding effects, the experiments were performed at pH 4 and 7, two conditions of charge density at the AgI surface, and three degrees of surface coverage. BSA adsorbed on hydrophobic AgI particles adopts a perturbed state. After release from the surface, the protein aggregates through surface-induced hydrophobic patches as indicated by a decrease in hydrophobicity together with an increase in beta -sheet content. This surface-induced aggregation is more pronounced at low pH and when the ratio of adsorbed/dissolved BSA increases but is independent of the AgI surface charge: A lower BSA concentration allows more time for the adsorbed molecules to relax at the sorbent surface.: At pH 4, the native BSA is less stable than at pH 7. Both these conditions promote structural changes upon adsorption, which results in released BSA molecules having a different conformation than that of the protein before adsorption.