Birchfield, A. S. | bioRxiv Science

bioRxiv2025

Structural and Biophysical Basis for PFAS Binding by Human Sterol Carrier Protein-2

Per- and polyfluoroalkyl substances (PFAS) are harmful environmental contaminants that bioaccumulate in human tissues and are linked to adverse health outcomes. While PFAS are known to bind to a variety lipid binding proteins (LBPs), such as human serum albumin and fatty acid-binding proteins (FABPs), the broader molecular basis for their biological distribution and additional target proteins in humans remains unanswered. Motivated by its known promiscuity towards a range of hydrophobic ligands, we investigated the interaction between human sterol carrier protein 2 (SCP2) and various PFAS. SCP2 is a structurally distinct LBP with no previously reported affinity for PFAS. Using a combination of screening, fluorescence displacement assays, protein structure prediction of PFAS-SCP2 complexes, ITC, and NMR experiments, we demonstrate for the first time that SCP2 is a PFAS-binding protein. Our findings provide insight into the residues participating in these interactions and provide evidence for an additional LBP that may facilitate PFAS distribution and persistence in the human body.

biophysics↗

bioRxiv2025

Broad PFAS binding with fatty acid binding protein 4 is enabled by variable binding modes.

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous pollutants that bioaccumulate in wildlife and humans, yet the molecular basis of their protein interactions remains poorly understood. Here, we show that human adipocyte fatty acid-binding protein (FABP4) can bind a diverse array of PFAS, including next-generation replacements for legacy chemicals and longer-chain perfluorocarboxylic acids. Shorter-chain PFAS, although weaker binders, still displayed measurable affinities--surpassing those of their nonfluorinated analogs. We determined crystal structures of FABP4 bound to perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), and perfluorohexadecanoic acid (PFHxDA), revealing three distinct binding modes. Notably, PFOA binds in two separate sites, and two distinct conformations define single-ligand binding of PFDA and PFHxDA. These arrangements enhance hydrophobic interactions within the binding cavity and likely explain the low micromolar dissociation constants observed in fluorescence competition assays. Our findings underscore the critical roles of chain length, headgroup functionality, and protein conformation in PFAS-FABP4 interactions. Given the emerging implications of the role of FABP4 in endocrine function, even subtle PFAS-induced perturbations could affect metabolic regulation and disease risk. Overall, this work highlights the value of direct structural and biochemical insights into PFAS-FABP4 interactions and paves the way for future research on PFAS transport and toxicological outcomes.

biophysics↗