SPECTROSCOPIC ANALYSIS AND MOLECULAR DOCKING STUDIES ON THE INTERACTION BETWEEN SILIBININ AND HUMAN SALIVARY α-AMYLASE

Abstract

The mechanism and detailed physico-chemical characterization of the interaction of Silibinin with Human Salivary α-amylase (HSAmy) is of great importance in understanding the pharmacokinetics and pharmacodynamic mechanism of Silibinin and HSAmy. Spectroscopic techniques and molecular docking were used to investigate the binding mode of Silibinin to HSAmy and results revealed that silibinin was able to quench the intrinsic fluorescence of HSAmy in a static manner of quenching mechanism. The number of binding sites, binding constants and thermodynamic parameters were calculated and results showed the non-spontaneous binding of Silibinin to only one active site on HSAmy with hydrophobic interactions playing a major role in the interaction and the binding constant was 8.0 × 10-2 at 298 K. HSAmy conformational and fluorophore microenvironment changes were studied using UV-Visible absorption and synchronous fluorescence measurements respectively and changes were observed to both the polypeptide chain and tryptophan microenvironment due to binding of Silibinin. There was nonradiative energy transfer between the donor (Silibinin- HSAmy complex) and acceptor (Silibinin) which were in close proximity. According to the molecular docking study, Silibinin is located at the active site of HSAmy and interacts mainly with hydrophobic amino acids (Trp 58. Trp 59, Tyr 62, Gln 63, Leu 162, Leu 165, Arg 192, Asp 197, Ala 198, His 209, Asp 300, Glu 233, Lys 352, Val 354 and Trp 257). This research showed a clear interaction between Silibinin and HSAmy elaborating the ligand properties of the enzyme which would be applicable in Silibinin or HSAmy based drug design.