Influence of Binding of Sodium Dodecyl Sulfate, All-trans-retinol, Palmitate, and 8-Anilino-1-naphthalenesulfonate on the Heat-Induced Unfolding and Aggregation of β-Lactoglobulin B

Heat treatment of bovine β-lactoglobulin B (β-LG) causes it to partially unfold and aggregate via hydrophobic association and intra- and interprotein disulfide bonds. The first stage, which involves a “loosening” of the native structure, is influenced by the environmental conditions, such as pressure, pH, and added solutes. In the present study, four potential β-LG ligands [palmitate, sodium dodecyl sulfate (SDS), 8-anilino-1-naphthalenesulfonate (ANS), and all-trans-retinol (retinol)] were added to β-LG solutions prior to heat treatment for 12 min at temperatures between 40 and 93 °C. The extent of the changes in secondary and tertiary structures, unfolding, and aggregation at 20 °C were determined by circular dichroism, fluorescence, and alkaline- and SDS−polyacrylamide gel electrophoresis (PAGE). Both palmitate and SDS stabilized the native structure of β-LG against heat-induced structural flexibility, subsequent unfolding, and denaturation. Retinol was less effective, probably because of its lower affinity for the calyx-binding site, and ANS did not stabilize β-LG, suggesting that ANS did not bind strongly in the calyx. It was also noted that holding a β-LG solution with added SDS or ANS promoted the formation of a hydrophobically associated non-native dimer. Keywords: SDS; ANS; retinol; palmitate; β-lactoglobulin B; heat-induced aggregation; binding site