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

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-1H-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 Kd 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.