The interaction mechanism of papain and bromelain with apigenin and luteolin in binary and ternary systems

In this study, the interaction mechanism of papain and bromelain with apigenin and luteolin in binary and ternary systems was compared and analyzed by spectroscopic methods, molecular docking, and molecular dynamics simulation. Additionally, the effects of apigenin and/or luteolin on the conformational changes and enzymatic activity of papain and bromelain were investigated. The results show that apigenin and/or luteolin exhibit a moderate binding affinity with papain/bromelain, with the binding constants K_a in the range of 10⁴–10⁵ L mol⁻¹. The order of addition of apigenin and luteolin significantly influenced their binding affinities to the enzymes. The main non-covalent forces of the papain-luteolin (first)-apigenin ternary system are hydrogen bonds and Van der Waals forces. Hydrophobic interactions, electrostatic forces and hydrogen bonds are the main non-covalent forces of other binary and ternary systems. These systems differentially alter the microenvironment of Trp and Tyr residues, secondary and tertiary structures, and enzymatic activity. Molecular docking and dynamics simulations identified specific binding sites of apigenin and/or luteolin on papain/bromelain, corroborating experimental findings. Notably, the ternary system exhibits a stronger inhibitory effect on papain activity compared to binary systems.