Chemical proteomics reveals human liver fatty acid binding protein as a predominant and selective target of triphenyl phosphate

Abstract

Triphenyl phosphate (TPHP) is a commonly used flame retardant and plasticizer with well-documented toxicity at environmentally relevant concentrations. We tested the hypothesis of covalent protein binding as a mechanism of TPHP toxicity by using chemical proteomics to identify adducted targets from human and rat hepatic proteomes. Results via in-gel fluorescent imaging showed that the TPHP-probe covalently bound many proteins with substantial interspecies variation. Using shotgun proteomics, we confirmed liver carboxylesterases as major targets in rat liver but identified liver fatty acid binding protein (L-FABP) as a novel and predominant target in human liver cells. The binding of TPHP to L-FABP was also confirmed by using recombinant L-FABP protein. We confirmed that TPHP binding to L-FABP is structurally selective, demonstrating that aryl side chains and the phosphate ester center are both essential for binding. Thus, we conclude that L-FABP is a predominant and selective target of TPHP in human hepatic proteome and that covalent protein adduction is an understudied toxicity mechanism for TPHP, presenting concerns regarding its widespread usage.