title: Refined apoprotein structure of rat intestinal fatty acid binding protein produced in Escherichia coli.
abstract: Rat intestinal fatty acid binding protein (I-FABP) is a member of a family of cytoplasmic hydrophobic ligand-binding proteins. To gain insights about the contribution of bound fatty acid to I-FABP's conformation and mechanism of ligand binding, we have determined the structure of Escherichia coli-derived rat apo-I-FABP to 1.96-A resolution and compared it to the recently refined structure of I-FABP with bound palmitate. Both apo- and holo-I-FABP are composed primarily of anti-parallel beta-strands which form two nearly orthogonal beta-sheets ("beta-clam"). The overall structures of the apo- and holo-I-FABP are nearly identical, with a root mean square (rms) difference of 0.37 A between C alpha atoms, 0.38 A between all main-chain atoms, and 0.94 A between all side-chain atoms. However, rms differences of greater than 1.3 A were noted for the side chains of Ile-23, Lys-27, Arg-56, Leu-72, Ala-73, and Asp-74. The space occupied by bound ligand in the core of the holoprotein is occupied in the apo-protein by ordered solvent molecules. This results in an increase in the total number of internal ordered solvent molecules from 7 in the holoprotein to 13 in apo-I-FABP. This finding, together with observed differences in the side-chain orientations of two residues (Arg-56 and Lys-27) situated over a potential opening to the cores of the apo- and holoproteins, suggests that solvent molecules play a critical role in ligand binding. Moreover, the data indicate that the beta-clam structure is stable even in the absence of bound ligand.
authors.affiliation: Department of Biochemistry, Washington University School of Medicine, Saint Louis, MO 63110.
authors.forename: J C
authors.initials: JC
authors.lastname: Sacchettini
authors.forename: J I
authors.initials: JI
authors.lastname: Gordon
authors.forename: L J
authors.initials: LJ
authors.lastname: Banaszak
mesh_terms: D001059:Apoproteins / Q000235:genetics / Q000302:isolation & purification; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification; D003460:Crystallization; D004926:Escherichia coli / Q000235:genetics*; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids / Q000378:metabolism; D008958:Models, Molecular; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000302:isolation & purification; D014961:X-Ray Diffraction
chemical_list: D001059:Apoproteins; D002352:Carrier Proteins; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins