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.
Abbreviations used: FABP, fatty acid-binding protein; A-FABP, adipocyte-type FABP; E-FABP, epidermal-type FABP; H-FABP, heart-type FABP; M-FABP, myelin-type FABP; I-FABP, intestinal-type FABP; ILBP, ileal lipid-binding protein; LBP, lipid-binding protein; NOE, nuclear Overhauser effect; HSQC, heteronuclear single-quantum coherence; RMSD, root-mean-square deviation; 2D, two-dimensional; 3D, three-dimensional.
Present address: Department of Immunology and Biochemistry, St. George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, U.K.
Present address: Institut für Rechtsmedizin, Universitätsklinikum Münster, Röntgenstrasse 23, D-48149 Münster, Germany.
The 1H and 15N resonance assignments for recombinant human E-FABP have been deposited at the BioMagResBank (http://www.bmrb.wisc.edu) under the accession number BMRB-5083. The atom co-ordinates of the 20 conformers representing the solution structure of human E-FABP have been deposited at the Research Collaboratory for Structural Bioinformatics (‘RCSB’) Protein Data Bank (http://www.rcsb.org) under the accession number 1JJJ.