Submitted on March 12, 2003
Revised on October 22, 2003
Accepted on October 29, 2003
Specificity determinants for lipids bound to
-barrel proteins
Amy J. Reese and Leonard J. Banaszak
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455
Corresponding Author: banas001{at}umn.edu
The family of proteins accountable for the intracellular movement of lipids is characterized by a 10-stranded
-barrel that forms an internalized cavity varying in size and binding preferences. The loop connecting
-strands E and F (fifth and sixth strands) is the most striking conformational difference between adipocyte lipid binding protein (ALBP) and cellular retinoic acid binding protein type I (CRABP I). The former has a preference for fatty acids while the latter binds retinoic acid. A three-residue mutation was made in wildtype ALBP (EF-ALBP) to mimic CRABP I. Crystal structures of ligand-free and EF-ALBP with bound oleic acid were solved to resolutions of 1.5 Å and 1.7 Å respectively. The structural results are compared with previous studies of WT-ALBP. The changes in three residues of one loop of the protein appear to have altered the positioning of the C18 fatty acid as observed in the electron density of crystalline EF-ALBP. However, there appears to be duplicity and disorder in the fatty acid positions. The crystallographic studies made it possible to compare the protein conformation and ligand positioning with that found in the wildtype protein. Although the cavity binding site in both the retinoid and fatty acid binding proteins is irregular, the superimposed coordinate data suggest only a relatively planar region of the cavity is used to accommodate the hydrophobic ligands. Preliminary chemical characterization of the mutant protein indicated changes in some binding properties and overall protein stability.