Understanding the interaction between α-1-acid glycoprotein (AGP) and potential Cu/Zn metallo-drugs of benzimidazole derived organic motifs: A multi-spectroscopic and molecular docking study

Drug-binding and interactions with plasma proteins strongly affect their efficiency of delivery, hence considered as a key factor in determining the overall pharmacological action. Alpha-1-acid glycoprotein (AGP), a second most abundant plasma protein in blood circulation, has unique drug binding ability and involved in the transportation of various compounds. Here, we have investigated the mechanism of interaction between AGP and potential Cu/Zn metallo-drugs of benzimidazole derived organic motifs (CuL₂ and ZnL₂, where L is Schiff base ligand) by applying integrated spectroscopic, biophysical techniques and computational molecular docking analyses. We found that both the metallo-drugs (CuL₂ and ZnL₂) were bound at the central cavity of AGP interacting with the residues of lobe I, lobe II as well as lobe III. The binding of metallo-drugs to AGP occurs in 1:1 M ratios. Hydrogen bonding, electrostatic and hydrophobic interactions played a significant role in stabilizing the AGP-metallo-drug complexes. Binding affinities of both the metallo-drugs towards AGP at 298 K were of the order of 10⁴-10⁵ M^-1, corresponding to Gibbs free energy of stabilization of approximately -5.50 to -6.62 kcal mol^-1. Furthermore, the spectroscopic investigation by circular dichroism and synchronous fluorescence analyses suggest conformational changes in AGP upon the binding of metallic compounds.