Insight into binding behavior, structure, and foam properties of α-lactalbumin/glycyrrhizic acid complex in an acidic environment

Abstract

Environmental changes such as pH can affect the binding interaction of protein and ligand. α-Lactalbumin (α-La) is viewed as a pervasive dietary protein and has the potential to act as a carrier for bioactive compounds. In this work, the binding behavior between α-La and glycyrrhizic acid (GA) in acidic (4.5 and 2.5) and neutral (7.0) conditions were explored by multi-spectroscopic, molecular docking, and molecular dynamics (MD) simulation methods. Initially, GA statically quenched the intrinsic fluorescence intensity of α-La under all conditions. Moreover, the secondary structure of α-La was disarranged in the presence of GA in acidic solution, as evidenced by the change in α-helix and β-sheet content of α-La from the circular dichroism (CD) and MD trajectory analyses. Importantly, there were inconspicuous effects of pH on the docking sites for the binding of α-La and GA, and these sites were mainly located in sheet S1, S2, or S3 and helix H4 or h1 in α-La. The foaming characteristics of the complex were analyzed according to foaming overrun. Relative to the neutral state, the foaming ability of α-La/GA and α-La was significantly increased by 33.24% at pH 7.0, while it was enhanced by 66.79% at pH 2.5. This study advances our understanding of the acid-induced α-La/GA complex and provides a theoretical basis for producing a protein-based foaming agent with excellent properties that could be widely used in the food, biomedical, and non-food industries.