Human FABP7 selectively captures docosahexaenoic acid over eicosapentaenoic acid: A potential protein-based platform for affinity purification of ω-3 lipids

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are principal omega-3 polyunsaturated fatty acids (PUFAs) nutritional and pharmaceutical interest. However, their near-isomeric structures render large-scale separation technically demanding and costly. Here we evaluate human fatty-acid-binding protein 7 (FABP7) as a biorecognition element capable of discriminating between these two lipids. Recombinant FABP7, expressed and purified from Escherichia coli , was analyzed for its binding affinity toward DHA and EPA by bio-layer interferometry (BLI). FABP7 bound DHA with an equilibrium dissociation constant K d  = 80.18 ± 3.71 mmol/m 3 , whereas binding to EPA was 7.5-fold weaker (K d  = 600.2 ± 30.2 mmol/m 3 ). Competitive BLI experiments confirmed that DHA efficiently displaced pre-bound EPA, while EPA was largely unable to remove DHA even at millimolar excess. These findings demonstrate that FABP7 possesses intrinsic molecular selectivity for DHA over EPA and could therefore serve as the affinity component of bio-based fractionation platforms. This work establishes a quantitative framework for engineering FABP-derived resins or sensors aimed at sustainable, low-energy purification of high-value ω-3 lipids.