Structural basis of the activation of PPARγ by the plasticizer metabolites MEHP and MINCH

Di-2-ethylhexyl phthalate (DEHP) and its substitute 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) are widely used as plasticizers but may have adverse health effects. Via hydrolysis of one of the two ester bonds in the human body, DEHP and DINCH form the monoesters MEHP and MINCH, respectively. Previous studies demonstrated binding of these metabolites to PPAR gamma and the induction of adipogenesis via this pathway. Detailed structural understanding of how these metabolites interact with PPAR gamma and thereby affect human health is lacking until now. We therefore characterized the binding modes of MINCH and MEHP to the ligand binding domain of PPAR gamma by X-ray crystallography and molecular dynamics (MD) simulations. Both compounds bind to the activating function-2 (AF-2) binding site via an interaction of the free carboxylates with the histidines 323 and 449, tyrosine 473 and serine 289. The alkyl chains form hydrophobic interactions with the tunnel next to cysteine 285. These binding modes are generally stable as demonstrated by the MD simulations and they resemble the complexation of fatty acids and their metabolites to the AF-2 site of PPAR gamma. Similar to the situation for these natural PPAR gamma agonists, the interaction of the free carboxylate groups of MEHP and MINCH with tyrosine 473 and surrounding residues stabilizes the AF-2 helix in the upward conformation. This state promotes binding of coactivator proteins and thus formation of the active complex for transcription of the specific target genes. Moreover, a comparison of the residues involved in binding of the plasticizer metabolites in vertebrate PPAR gamma orthologs shows that these compounds likely have similar effects in other species.

Automated summary

Di-2-ethylhexyl phthalate (DEHP) and its substitute 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) are plasticizers that can hydrolyze in the human body to form metabolites that bind to PPARγ and induce adipogenesis. This study characterized the binding modes of these metabolites using X-ray crystallography and molecular dynamics simulations. The metabolites bind to the AF-2 binding site of PPARγ and stabilize the AF-2 helix in an upward conformation, promoting the formation of the active complex for transcription. Comparisons with other species suggest similar effects of these plasticizer metabolites.