Non-native States of Bovine Beta-Lactoglobulin Induced by Acetonitrile: pH-Dependent Unfolding of the Two Genetic Variants A and B

Acetonitrile (ACN)-induced unfolding of the beta-lactoglobulin variants A and B was investigated at pH 2.0, 7.0 and 9.0. ACN caused α-helix induction at low concentrations but lead to major conformational alterations when the concentration was raised. ACN also induced a concentration-dependent increase in the surface hydrophobicity of both the variants. Induction of α-helical structure and exposure of hydrophobic patches were, however, somewhat more pronounced in case of variant B, whereas the loss of tertiary structure was more marked for variant A. Both protein aggregation and helix induction necessitated higher ACN concentrations at pH 2.0 than at 7.0 and 9.0, suggesting the greater stability of the variants at acidic pH.