Stability and gelation behavior of bovine serum albumin pre-aggregates in the presence of calcium chloride

Abstract

We study, using wide-angle and small-angle light scattering techniques, the stability and aggregation/gelation behaviors of denatured filamentous bovine serum albumin pre-aggregates (BSA-PAs), induced by CaCl₂. It is observed that transparent filamentous gels can be formed not only at low CaCl₂ concentrations but also at high CaCl₂ concentrations, while turbid gels are obtained at intermediate CaCl₂ concentrations. Although the filamentous gels at low CaCl₂ concentrations and the turbid gels at intermediate CaCl₂ concentrations are consistent with the literature observations, the filamentous gels at high CaCl₂ concentrations have to be explained by different mechanisms. The latter is attributed to the repulsive hydration interactions originating from increased surface dipoles generated by counterion binding. Since such surface dipole-induced hydration is very short-range and occurs mainly on charged or polar patches of proteins (thus protected from aggregation), the aggregation of the filamentous BSA-PAs at hydrophobic patches at the two ends is still possible, leading to formation of the filamentous gels.