Structural insights into PFAS-β-lactoglobulin binding mechanism mediating PFAS toxicity.

Area of Science:

• Biochemistry
• Toxicology
• Structural Biology

Background:

• Per- and polyfluoroalkyl substances (PFAS) are persistent, toxic environmental contaminants due to strong carbon-fluorine bonds.
• Beta-lactoglobulin (BLG), a milk protein, is known to transport hydrophobic compounds essential for biological functions.
• Understanding BLG's interaction with PFAS is crucial due to potential health implications.

Purpose of the Study:

• To investigate the binding mechanism of PFAS with beta-lactoglobulin.
• To determine the structural basis for PFAS interaction with BLG.
• To assess the stability and affinity of PFAS-BLG complexes.

Main Methods:

• X-ray crystallography was used to determine the structures of BLG complexed with PFOA, PFOS, and PFDA.
• Molecular dynamics (MD) simulations were employed to analyze binding stability and energetics.
• Comparative structural analysis was performed between apo-BLG and PFAS-bound BLG.

Main Results:

• Crystal structures revealed high-affinity binding of PFOA, PFOS, and PFDA within the central calyx of BLG, the known site for retinol and fatty acid binding.
• Hydrophobic interactions stabilize the binding of PFAS "tails," while polar interactions occur with BLG residues Lys60 and Lys69.
• MD simulations confirmed the stability of PFAS binding, with PFDA exhibiting the highest binding energy (-25 kcal/mol) due to favorable van der Waals interactions with its longer hydrophobic chain.

Conclusions:

• Beta-lactoglobulin effectively binds PFAS, utilizing its canonical hydrophobic binding pocket.
• The protein's structure undergoes conformational changes, including an open EF loop, upon PFAS complexation.
• BLG may act as a transporter for PFAS, potentially influencing their distribution and mediating neurotoxic effects.