Interaction Behavior Between Niclosamide and Pepsin Determined by Spectroscopic and Docking Methods

Abstract

The interaction between niclosamide (NIC) and pepsin was investigated using multispectroscopic and molecular docking methods. Binding constant, number of binding sites, and thermodynamic parameters at different temperatures were measured. Results of fluorescence quenching and synchronous fluorescence spectroscopy in combination with three-dimensional fluorescence spectroscopy showed that changes occurred in the microenvironment of tryptophan residues and the molecular conformation of pepsin. Molecular interaction distance and energy-transfer efficiency between pepsin and NIC were determined based on Förster nonradiative energy-transfer mechanism. Furthermore, the binding of NIC inhibited pepsin activity in vitro. All these results indicated that NIC bound to pepsin mainly through hydrophobic interactions and hydrogen bonds at a single binding site. In conclusion, this study provided substantial molecular-level evidence that NIC could induce changes in pepsin structure and conformation.

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“…If both $$$ \Delta {\mathbf{H}}_{\mathbf{0}} $$$ and $$$ \Delta {\boldsymbol{S}}_{\mathbf{0}} $$$ are more than zero, this means that hydrophobic interactions are dominant. When $$$ \Delta {\mathbf{H}}_{\mathbf{0}} $$$ is negative and $$$ \Delta {\boldsymbol{S}}_{\mathbf{0}} $$$ is positive, it is suggested that the main driving forces are electrostatic interactions [49]. As shown in Table 2 $$$ \Delta {\mathbf{H}}_{\mathbf{0}} $$$ <0 and $$$ \Delta {\boldsymbol{S}}_{\mathbf{0}} $$$ >0 indicate that the major forces contributing to the interaction of AMX with EB were electrostatic interactions (Figure 9).…”

“…If both ΔH 0 and ΔS 0 are more than zero, this means that hydrophobic interactions are dominant. When ΔH 0 is negative and ΔS 0 is positive, it is suggested that the main driving forces are electrostatic interactions[49].S C H E M E 2 Proposed mechanism of reaction for the formation of a non-fluorescence ion-pair complex between AMX and EB T A B L E 1 Stern-Volmer for the reaction of AMX and EB Drug Temperature (K) Stern-Volmer quenching constant. (K sv ) Â 10 3 (L/mol) Correlation coefficient (r) Bimolecular quenching constant (K q ) Â 10…”