Probing the toxicity of long-chain fluorinated surfactants: Interaction mechanism between perfluorodecanoic acid and lysozyme

It is of great significance to study the potential toxicity and the mechanism of long-chain fluorinated surfactants. In this paper, the binding mechanism of perfluorodecanoic acid (PFDA) to an immunoactive substance, lysozyme (LYZ), was explored by spectroscopy, thermodynamics, enzyme activity assay and molecular simulation under simulated physiological conditions. Results suggested that the binding of PFDA and LYZ was mainly driven by Van der Waals' forces and hydrogen bond forces. This interaction resulted in the contraction of molecular framework, and greatly changed secondary structure of LYZ as well as microenvironment around aromatic amino acids. Molecular simulation suggested that PFDA preferred to bind to Ser-50 and Trp-62 in the enzyme activity center. The competitive effect between PFDA and substrate at the active site and the change of LYZ structure led to significant reduction of LYZ activity. Moreover, the fluorescence sensitization of LYZ arose from the surfactant property of PFDA and its binding to Trp-62. These results suggested that PFDA damages molecular structure and function of LYZ greatly. This study provides detailed basic data on the toxicity of PFDA at the molecular level and has implications for the immunotoxicity of long-chain fluorinated surfactants to humans. (C) 2019 Published by Elsevier B.V.