Interaction kinetics of liposome-incorporated unsaturated fatty acids with fatty acid-binding protein 3 by surface plasmon resonance.

Abstract The role of heart-type fatty acid-binding protein (FABP3) in human physiology as an intracellular carrier of fatty acids (FAs) has been well-documented. In this study, we aimed to develop an analytical method to study real-time interaction kinetics between FABP3 immobilized on the sensor surface and unsaturated C18 FAs using surface plasmon resonance (SPR). To establish the conditions for SPR experiments, we used an FABP3-selective inhibitor 4-(2-(1-(4-bromophenyl)-5-phenyl-1 H -pyrazol-3-yl)-phenoxy)-butyric acid. The affinity index thus obtained was comparable to that reported previously, further supporting the usefulness of the SPR-based approach for evaluating interactions between FABPs and hydrophobic ligands. A pseudo-first-order affinity of FABP3 to K + petroselinate (C18:1 Δ6 cis ), K + elaidate (C18:1 Δ9 trans ), and K + oleate (C18:1 Δ9 cis ) was characterized by the dissociation constant ( K d ) near micromolar ranges, whereas K + linoleate (C18:2 Δ9,12 cis / cis ) and K + α-linolenate (C18:3 Δ9,12,15 cis / cis / cis ) showed a higher affinity to FABP3 with K d around 1 × 10 −6  M. Interactions between FAPB3 and C18 FAs incorporated in large unilamellar vesicles consisting of 1,2-dimyristoyl- sn -glycero-3-phosphocholine and FAs (5:1 molar ratio) were also analysed. Control DMPC liposomes without FA showed only marginal binding to FABP3 immobilized on a sensor chip while liposome-incorporated FA revealed significant responses in sensorgrams, demonstrating that the affinity of FAs to FABP3 could be evaluated by using the liposome-incorporated analytes. Significant affinity to FABP3 was observed for monounsaturated fatty acids ( K d in the range of 1 × 10 −7  M). These experiments demonstrated that highly hydrophobic compounds in a liposome-incorporated form could be subjected to SPR experiments for kinetic analysis.