To understand the binding mechanism of a mixture of chiral phenothrin with human serum albumin (HSA), we used multi-spectroscopy, including steady-state fluorescence spectroscopic titration, three-dimensional fluorescence spectroscopy, circular dichroism, and FTIR spectra to explore the precise interactions between the complex. Based on the modified Stern-Volmer equation, the binding constant (Ka) was calculated under three temperatures, which revealed that phenothrin interacts with HSA through a static quenching mechanism. The thermodynamic parameters including enthalpy change (ΔH) and entropy change (ΔS) were determined by fitting the experimental data with van't Hoff equation, which indicates that electrostatic force and hydrogen bonds dominate the interplay in the phenothrin-HSA complex. Circular dichroism and FTIR showed the addition of phenothrin changed the secondary structure of proteins, in which the α-helicity decreased from 52.37% in free HSA to 50.02%. The esterase-like activity was reduced with the increase of phenothrin concentration, which may be attributed to the perturbated senior structure of HSA. Competitive displacement experiments confirmed that phenothrin inserted into the subdomain IIA (site I) of HSA. Several computational approaches such as molecular docking, frontier molecular orbital analysis, and electrostatic potential analysis were utilized to probe into the binding mode of the phenothrin-HSA complex. The binding behaviors of the chiral phenothrin mixture differed during the complexation. In conclusion, both the experimental and theoretical investigations provide useful information for better understanding and reducing the potential deleterious effects of the chiral phenothrin mixture on human long-term physio-pathological status.
Keywords: Esterase-like activity; Human serum albumin; Molecular docking; Multi-spectroscopy; Phenothrin.
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