High-throughput protein target mapping enables accelerated bioactivity discovery for ToxCast and PFAS compounds.

Chemical pollution is a global threat to human health, yet the toxicity mechanisms of most contaminants remains unknown. Here, we applied an ultrahigh-throughput affinity selection-mass spectrometry (AS-MS) platform to systematically identify protein targets of prioritized chemical contaminants. After benchmarking the platform, we screened 50 human proteins against 481 prioritized chemicals, including 446 ToxCast chemicals and 35 per- and polyfluoroalkyl substances (PFAS). Among 24,050 interactions assessed, we discovered 35 interactions involving 13 proteins, with fatty acid-binding proteins (FABPs) emerging as the most ligandable protein family. Given this, we selected FABPs for further validation, which revealed a distinct PFAS binding pattern: legacy PFAS selectively bound to FABP1, whereas replacement compounds, perfluoroether carboxylic acids, unexpectedly interacted with all FABPs. X-ray crystallography further revealed that the ether group enhances the molecular flexibility of alternative PFAS to accommodate the binding pockets of FABPs. Our findings demonstrate that AS-MS is a robust platform for the discovery of protein targets beyond the scope of ToxCast and highlight the broader protein-binding spectrum of alternative PFAS as potential regrettable substitutes.