Interactions of 1-hydroxypyrene with bovine serum albumin: insights from multi-spectroscopy, docking and molecular dynamics simulation methods

Abstract

The interaction between a typical PAH metabolite, 1-hydroxypyrene (1-OHP), and a transport protein, bovine serum albumin (BSA), has been investigated using fluorescence, UV-visible absorption (UV-vis), circular dichroism (CD) spectra, docking and molecular dynamics (MD) simulation methods under simulated physiological conditions (in Tris–HCl buffer, pH = 7.40). The experimental results suggested that the fluorescence quenching of BSA by 1-OHP occurred through a mixed static and dynamic quenching mechanism with a binding constant of 2.40 × 10⁶ L mol⁻¹ at 291 K. The thermodynamic parameters together with the docking and MD study revealed that van der Waals forces dominate the formation of the 1-OHP–BSA complex. Applying Förster's non-radiation energy transfer theory, the binding distance of 1-OHP to BSA was calculated to be 2.88 nm. In addition, as confirmed by time-resolved fluorescence, UV-vis, three-dimensional (3-D) fluorescence and CD spectra, high concentrations of 1-OHP induced conformational transitions of BSA, increasing the content of the α-helix of BSA and exposing its tryptophan residue to a more hydrophilic microenvironment. An inhibition test showed that 1-OHP strongly inhibits the binding constant of vitamin B₂ with BSA. A molecular docking study visualized the binding mode of 1-OHP with BSA. 1-OHP inserted into the binding pocket IB of BSA, leaving its hydroxyl group outside. Based on that, the MD study further unveiled the stability of 1-OHP–BSA complex and their dynamic binding modes, and clarified the contributions of each binding force component and the key residues to the binding process.