title: Structural and biochemical characterization of toad liver fatty acid-binding protein.
abstract: Two paralogous groups of fatty acid-binding proteins (FABPs) have been described in vertebrate liver: liver FABP (L-FABP) type, extensively characterized in mammals, and liver basic FABP (Lb-FABP) found in fish, amphibians, reptiles, and birds. We describe here the toad Lb-FABP complete amino acid sequence, its X-ray structure to 2.5 A resolution, ligand-binding properties, and mechanism of fatty acid transfer to phospholipid membranes. Alignment of the amino acid sequence of toad Lb-FABP with known L-FABPs and Lb-FABPs shows that it is more closely related to the other Lb-FABPs. Toad Lb-FABP conserves the 12 characteristic residues present in all Lb-FABPs and absent in L-FABPs and presents the canonical fold characteristic of all the members of this protein family. Eight out of the 12 conserved residues point to the lipid-binding cavity of the molecule. In contrast, most of the 25 L-FABP conserved residues are in clusters on the surface of the molecule. The helix-turn-helix motif shows both a negative and positive electrostatic potential surface as in rat L-FABP, and in contrast with the other FABP types. The mechanism of anthroyloxy-labeled fatty acids transfer from Lb-FABP to phospholipid membranes occurs by a diffusion-mediated process, as previously shown for L-FABP, but the rate of transfer is 1 order of magnitude faster. Toad Lb-FABP can bind two cis-parinaric acid molecules but only one trans-parinaric acid molecule while L-FABP binds two molecules of both parinaric acid isomers. Although toad Lb-FABP shares with L-FABP a broad ligand-binding specificity, the relative affinity is different.
authors.affiliation: Instituto de Química y Fisicoquímica Biológicas (IQUIFIB)-CONICET-UBA, Facultad de Farmacia y Bioquímica, UBA, Junín 956, Buenos Aires 1113, Argentina. sdipietro@mednet.ucla.edu
authors.forename: Santiago M
authors.initials: SM
authors.lastname: Di Pietro
authors.forename: Betina
authors.initials: B
authors.lastname: Córsico
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Perduca
authors.forename: Hugo L
authors.initials: HL
authors.lastname: Monaco
authors.forename: José A
authors.initials: JA
authors.lastname: Santomé
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002022:Bufo arenarum; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D002851:Chromatography, High Pressure Liquid; D019143:Evolution, Molecular; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D002352:Carrier Proteins; C493320:Fabp1 protein, mouse; C493321:Fabp1 protein, rat; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins