Characterization of Interaction Between Low-Density Lipoprotein (LDL) and Alkaloid N-Methyl Cytisine: The Potential Protective Effect on Lipid Oxidation

Elevated levels of low-density lipoprotein (LDL) in the blood are one of the main risk factors for atherosclerosis and coronary heart disease. Oxidized LDL (ox-LDL) plays an important role in the pathogenesis of atherogenesis. The interaction of LDL with natural alkaloids may exert a protective effect on the oxidation of lipoproteins. In this study, the binding of N-methylcytisine (NMC) to LDL is examined at the molecular level, and its role in LDL oxidation is investigated. LDL was isolated by ultracentrifugation and quantitatively characterized, by the Bradford technique, using the SDS-PAGE technique with a resolution of 8% and size was measured by dynamic light scattering (DLS). The characteristic bands attributed to the functional groups of the lipoproteins in the isolated fraction, were analyzed by Fourier transform infrared spectroscopy (FTIR-ATR). Using UV–visible, Raman, FTIR and fluorescence spectroscopies, we found that LDL interacts with the alkaloid NMC and has a protective effect against LDL oxidation. Protein-protein and ligand-protein docking methods were used to construct a molecular model for the complex between the I domain of apoprotein B100 and NMC. Our results indicate that the binding of NMC to LDL lipoprotein occurs in the I-domain of apoB-100 and involves polar and hydrophobic residues.