Study on the interactions between nicotine γ-rezocine formic acid salt and pepsin: Multispectroscopy, molecular docking, and molecular dynamics simulation

Abstract

Nicotine salt is a new form of nicotine introduced in tobacco products, and its interaction with biological macromolecules may be different from free nicotine, thereby affecting the absorption, metabolism, and physiological activity of nicotine in vivo. To explore the transport mechanism of nicotine salt into the gastrointestinal tract, this work firstly prepared a single crystal of nicotine γ-rezocine formic acid salt (named DBN) and then analyzed the interaction of DBN with pepsin (PEP) via multispectral methods and simulation technology. The results of single-crystal diffraction showed that the chemical formula of DBN was C17H20N2O4, and the crystal was closely bound by electrostatic interaction (ionic bond). DBN quenched the endogenous fluorescence of PEP by static quenching, and the binding strength between them was moderate (Ka = 8006 L·mol−1, 310 K). Thermodynamic parameters implied that the binding was a spontaneous process driven by hydrophobic forces. Investigations on the PEP conformation showed that DBN had a considerable effect on the amino acid microenvironment of PEP and reduced the hydrophobicity of PEP. Molecular docking and MD simulation results further supplemented and verified that DBN could stably combine in the hydrophobic cavity of PEP.