Spectroscopy and molecular docking studies on the binding of propyl gallate to human serum albumin

The interaction of propyl gallate (PG) with human serum albumin (HSA) was investigated by fluorescence, far-UV CD and FT-IR spectroscopic methods as well as molecular docking. Fluorescence emission spectra demonstrated that the HSA fluorescence was quenched by PG through static quenching and energy transfer with the binding constants in the order of 105 L mol−1. The thermodynamic parameters (ΔH=−29.64 KJ mol−1, ΔS=2.7 J mol−1 K−1) indicated that both hydrophobic force and hydrogen bond interactions played a leading role in the formation of PG-HSA complex. The results also showed the existence of a single binding site, which was located in subdomain IIA (site I) as revealed by molecular docking and competitive binding experiments. Molecular docking studies further showed the participation of several amino acids in PG-HSA complexation, which stabilized by H-bonding systems. The synchronous fluorescence spectra showed that the binding of drug caused the environment of tryptophan residues became more polar. FT-IR and CD spectroscopic further showed that drug complexation altered protein conformation by a major reduction of α-helix inducing a partial protein destabilization.