Characterization of the interaction between acotiamide hydrochloride and human serum albumin: 1H STD NMR spectroscopy, electrochemical measurement, and docking investigations

The interaction between acotiamide hydrochloride (Z-338) and human serum albumin (HSA) was investigated by multiple spectroscopic analyses, electrochemical approaches, and computer-aided molecular docking studies. H-1 nuclear magnetic resonance (NMR) spectroscopy and saturation transfer difference (STD) data indicated that Z-338 weakly interacted with HSA. STD signals showed that the benzene and five-membered rings of Z-338 were responsible for the binding efficiency. Fluorescence lifetime measurements implied that Z-338 quenched the intrinsic fluorescence of HSA with a new complex formation via static mode. Key parameters regarding this interaction were calculated from differential pulse voltammetry and fluorescence spectroscopy. Results obtained from the two methods above ascertained the static mechanism and revealed that hydrogen bonding combined with van der Waals forces played a major role in HSA-Z-338 binding. Although the displacement of probes from both sites I and II was observed from competitive STD-NMR experiments, molecular docking results suggested that Z-338 was preferentially bound to site II of HSA. This finding was supported by the esterase-like activity result. A decrease in the esterase-like activity of HSA after Z-338 binding showed that the Arg-410 and Tyr-411 of subdomain IIIA were directly involved in the binding process, which corroborated the accuracy of docking studies. Furthermore, circular dichroism spectra, Fourier transform infrared spectroscopy, and 3D fluorescence demonstrated that Z-338 slightly disturbed the microenvironment of amino residues and affected the secondary structure of HSA. Overall, this study provides valuable information to further understand the use of Z-338.