Static and Dynamic Scattering of β-Lactoglobulin Aggregates Formed after Heat-Induced Denaturation at pH 2

Abstract

The structure and internal dynamics of β-lactoglobulin aggregates formed after heat-induced denaturation at pH 2 and different ionic strengths were investigated using light, neutron, and X-ray scattering. Polydisperse aggregates are formed with a rigid rodlike local structure with mass per unit length close to that of a string of β-lactoglobulin monomers but with a somewhat larger diameter. The persistence length decreases with increasing ionic strength from more than 600 nm at 0.013 M to 38 nm at 0.1 M. At ionic strengths of 0.1 and 0.2 M, a self-similar structure with fractal dimensions of 1.8 and 2.0 is seen by using light scattering. The concentration dependence of the static structure factor and the internal dynamics are close to those of flexible linear chains. In contrast, a rigid behavior is observed at lower ionic strength (0.03 and 0.013 M). The persistence length of aggregates formed at 0.013 M is reduced after dilution in 0.1 and 0.2 M ionic strength solvents but remains larger than that of aggregates formed and diluted in 0.1 and 0.2 M. The ionic strength of formation is thus a determining factor for the structure. At pH 2, there is no evidence for a two-step aggregation process as was observed at pH 7.