Stabilization of apo α-lactalbumin by binding of epigallocatechin-3-gallate: Experimental and molecular dynamics study

Abstract

α-Lactalbumin (ALA) is a Ca²⁺-binding protein which constitutes up to 20% of whey protein. At acidic pH, and in the apo-state at elevated temperatures, ALA is the classic 'molten globule' (MG). This study examined epigallocatechin-3-gallate (EGCG) binding to ALA in its apo form (apoALA) and stabilizing effect on protein structure thereof. EGCG binds to apoALA in both native and MG state. The complex of EGCG and ALA is more stable to thermal denaturation. The docking analysis and molecular dynamic simulation (MDS) showed that Ca²⁺ removal decreased conformational stability of ALA, because of the local destabilization of Ca²⁺-binding region. EGCG binding to apoALA increases its stability by reverting of conformation and stability of Ca²⁺-binding region. Therefore, EGCG-induced thermal stability of apoALA is based on increased apoALA conformational rigidity. This study implies that during gastric digestion of tea with milk EGCG would remain bound to ALA, albeit in the Ca²⁺-free form.

Keywords: Apo α-lactalbumin; Epigallocatechin-3-gallate; Fluorescence quenching; Molecular dynamics simulation; Noncovalent interactions; Protein stability.