Studies on Molecular Interactions between Bovine β-Lactoglobulin and Silver Nanoparticles

Background: Silver Nanoparticles (AgNPs) were found to modulate the fibrillation of Bovine -Lactoglobulin (BLG). Objective: To gain an insight regarding the mechanism of BLG aggregation modulation by AgNPs at molecular level, studies on the interactions between BLG and AgNPs were carried out. Methods: Protein-ligand interactions were studied based on Trp fluorescence quenching (at four different temperatures), synchronous and three-dimensional fluorescence and circular dichroism spectroscopy (far-UV and near-UV). Results: Protein-nanoparticles association constant was in the range of 10⁶ -10¹⁰ M^-1 and the quenching constant was determined as ~10⁷ M^-1. Ground state complexation between the protein and nanoparticles was predicted. Change in polarity surrounding the Trp residue was not detected by synchronous and three-dimensional fluorescence spectroscopy. AgNPs caused a global change in the secondary and tertiary structure of the protein as revealed from far-UV and near-UV CD spectroscopy. Enthalpy driven complexation between the protein and nanoparticles indicates the involvement of hydrogen bonding and/or van der Waals interactions. Conclusion: Modulation of BLG aggregation by AgNPs is due to strong binding of the nanoparticles with BLG, which also causes structural perturbations of the protein.