The association of the adipocyte lipid-binding protein (ALBP) with arachidonic acid (all cis, 20:4 Δ5,8,11,14) and oleic acid (cis, 18:1 Δ9) has been examined by titration calorimetry. In addition, the crystal structure of ALBP with bound arachidonic acid has also been obtained. Crystallographic analysis of the arachidonic acid-ALBP complex along with the previously reported oleic acid-ALBP structure (Xu, Z., Bernlohr, D. A., and Banaszak, L. J. (1993) J. Biol. Chem. 268, 7874-7884) provides a framework for the molecular examination of protein-lipid association. Isothermal titration calorimetry revealed high affinity association of both unsaturated fatty acids with the protein. The calorimetric data yielded the following thermodynamic parameters for arachidonic acid: K(d) = 4.4 μM, n = 0.8, ΔG = -7370 cal/mol, ΔH = -6770 cal/mol, and TΔS = +600 cal/mol. For oleic acid, the thermodynamic parameters were K(d) = 2.4 μM, n = 0.9, ΔG = -7770 cal/mol, ΔH = -6050 cal/mol, and TΔS = +1720 cal/mol. The identification of thermodynamically dominating enthalpic factors for both fatty acids are consistent with the crystallographic studies demonstrating the interaction of the fatty acid carboxylate with a combination of Arg106, Arg126, and Tyr128. The crystallographic refinement of the protein-arachidonate complex was carried out to 1.6 Å with the resultant R factor of 0.19. Within the cavity of the crystalline binding protein, the arachidonate was found in a hairpin conformation. The conformation of the bound ligand is consistent with acceptable torsional angles and the four cis double bonds in arachidonate. These results demonstrate that arachidonate is a ligand for ALBP. They provide thermodynamic and structural data concerning the physical basis for protein-lipid interaction and suggest that intracellular lipid- binding proteins may mediate the biological effects of polyunsaturated fatty acids in vivo.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|State||Published - 1994|