New insight into the alcohol induced conformational change and aggregation of the alkaline unfolded state of bovine β-lactoglobulin

Abstract

Accumulation of ordered protein aggregates (or amyloids) is responsible for several neurodegenerative diseases. β-Lactoglobulin (β-lg) an important globular milk protein, self-assembles to form amyloid-like fibrils on heating at low pH. But here we report for first time the self-assembly of β-lg from its alkaline unfolded state. The present work describes the folding and self-assembly of β-lg from a reversible unfolded state at pH 10.5 in the presence of methanol, 2-propanol, t-butanol and 2,2,2-trifluoroethanol (TFE). The extent of secondary and tertiary structure formation is in the order methanol < 2-propanol < t-butanol < TFE. Exposure of the hydrophobic core of the protein molecules in an apolar environment of TFE seems to promote intermolecular cluster formation. Methanol and TFE induce aggregation through the α-helical structure whereas isopropanol and t-butanol favour the formation of the β-structure leading to aggregation at higher concentrations. In vitro aggregation generates various nanometer structures such as nanofibrils, nanovesicles and nanotubes depending on the nature and concentration of the alcohols.