Solution structure and backbone dynamics of human epidermal-type fatty acid-binding protein (E-FABP)

Human epidermal-type fatty acid-binding protein (E-FABP) belongs to a family of intracellular 14–15kDa lipid-binding proteins, whose functions have been associated with fatty acid signalling, cell growth, regulation and differentiation. As a contribution to understanding the structure—function relationship, we report in the present study features of its solution structure and backbone dynamics determined by NMR spectroscopy. Applying multi-dimensional high-resolution NMR techniques on unlabelled and ¹⁵N-enriched recombinant human E-FABP, the ¹H and ¹⁵N resonance assignments were completed. On the basis of 2008 distance restraints, the three-dimensional solution structure of human E-FABP was subsequently obtained (backbone atom root-mean-square deviation of 0.92±0.11Å; where 1Å = 0.1nm), consisting mainly of 10 anti-parallel β-strands that form a β-barrel structure. ¹⁵N relaxation experiments (T₁, T₂ and heteronuclear nuclear Overhauser effects) at 500, 600 and 800MHz provided information on the internal dynamics of the protein backbone. Nearly all non-terminal backbone amide groups showed order parameters S²>0.8, with an average value of 0.88±0.04, suggesting a uniformly low backbone mobility in the nanosecond-to-picosecond time range. Moreover, hydrogen/deuterium exchange experiments indicated a direct correlation between the stability of the hydrogen-bonding network in the β-sheet structure and the conformational exchange in the millisecond-to-microsecond time range. The features of E-FABP backbone dynamics elaborated in the present study differ markedly from those of the phylogenetically closely related heart-type FABP and the more distantly related ileal lipid-binding protein, implying a strong interdependence with the overall protein stability and possibly also with the ligand-binding affinity for members of the lipid-binding protein family.