In Vitro and In Silico Evaluations of Binding Affinities of Perfluoroalkyl Substances to Baikal Seal and Human Peroxisome Proliferator-Activated Receptor α

In this study, we assessed the binding affinities of perfluoroalkyl substances (PFASs), including perfluoroalkyl carboxylates (PFCAs) and perfluoroalkyl sulfonates (PFSAs), to the ligand-binding domains (LBDs) of Baikal seal (Pusa sibirica; bs) and human (h) peroxisome proliferator-activated receptor alpha (PPAR alpha). An in vitro competitive binding assay showed that six PFCAs and two PFSAs could bind to recombinant bs and hPPAR alpha LBD proteins in a dose dependent manner. The relative binding affinities (RBAs) of PFASs to bsPPAR alpha were as follows: PFOS > PFDA > PFNA > PFUnDA > PFOA > PFHxS > PFHpA > PFHxA. The RBAs to bsPPAR alpha showed a significant positive correlation with those to hPPAR alpha. In silico PPAR alpha homology modeling predicted that there were two ligand-binding pockets (LBPs) in the bsPPAR alpha and hPPAR alpha LBDs. Structure-activity relationship analyses suggested that the binding potencies of PFASs to PPAR alpha might depend on LBP binding cavity volume, hydrogen bond interactions, the number of perfluorinated carbons, and the hydrophobicity of PFASs. Interspecies comparison of the in vitro binding affinities revealed that bsPPAR alpha had higher preference for PFASs with long carbon chains than hPPAR alpha. The in silico docking simulations suggested that the first LBP of bsPPAR alpha had higher affinities than that of hPPAR alpha; however, the second LBP of bsPPAR alpha had lower affinities than that of hPPAR alpha. To our knowledge, this is the first evidence showing interspecies differences in the binding of PFASs to PPAR alpha s and their structure activity relationships.