Molecular insights into the interaction of 5-fluorouracil and Fe3O4 nanoparticles with beta-casein: An experimental and theoretical study

Abstract

We investigated the potential carrier of milk beta-casein (β-CN) and its interactions with 5-fluorouracil (5-FU) and iron oxide nanoparticles (Fe3O4 NPs). We used different spectroscopic methods of fluorescence, UV–Visble, circular dichroism (CD), synchronous fluorescence, zeta potential assay, and computational studies to clarify the protein interaction with 5-FU and Fe3O4 NPs. The fluorescence data indicated both Fe3O4 NPs and 5-FU could quench the intrinsic fluorescence of β-CN. Fluorescence measurements showed that the single interaction of β-CN with 5-FU or Fe3O4 NPs was static, while reacted β-CN with both 5-FU and Fe3O4 NPs simultaneously showed a dynamic quenching. Synchronous fluorescence data in both tests revealed that the tryptophan (Trp) residue of β-CN had a dominant role in quenching and the polarity of its microenvironment more than tyrosine (Tyr) increased in interaction with 5-FU. All the binding sites and thermodynamic parameters were obtained at 25, 37, and 42 °C. The analysis of thermodynamic parameters and Job’s plot techniques pointed to that both of these complexes with the 1:1 M ratio were exothermic (ΔH°<0) driven with the van der Waals and H-bonding interactions (in agreement with the docking results). The CD spectra in the region of far-UV and thermal denaturation study indicated minor changes in the secondary structure of β-CN in the presence of various concentrations of Fe3O4 NPs and 5-FU. Also, from the molecular dynamics (MD) analysis, as a result, the protein structure was stable during 100 ns. The outcomes highlighted that β-CN protein could form a great bind with 5-FU and Fe3O4 NPs ligands (supporting the zeta potential assay results) by independent binding sites. These results would be helpful insight to construct a potential magnetic nanocarrier β-CN base for 5-FU drug delivery.