title: Ligand-binding specificity of an invertebrate (Manduca sexta) putative cellular retinoic acid binding protein.
abstract: Intracellular lipid-binding proteins (iLBPs) are small cytoplasmic proteins that specifically interact with hydrophobic ligands. Fatty acid-binding proteins (FABPs), cellular retinoic acid-binding proteins (CRABPs) and cellular retinol-binding proteins (CRBPs) belong to the iLBP family. A recently identified insect (Manduca sexta) iLBP has been reported to possibly represent an invertebrate CRABP mimicking the role of CRABPs in vertebrate organisms. The presence in this protein of the characteristic binding triad residues involved in the interaction with ligand carboxylate head groups, a feature pertaining to several FABPs and to CRABPs, and the close phylogenetic relationships with both groups of vertebrate heart-type FABPs and CRBPs/CRABPs, makes it difficult to assign it to either FABPs or CRABPs. However, its negligible interaction with retinoic acid and high affinity (K(d) values in the 10(-8) M range) for fatty acids have been established by means of direct and competitive binding assays. As shown by phylogenetic analysis, the M. sexta iLBP belongs to a wide group of invertebrate iLBPs, which, besides being closely related phylogenetically, share distinctive features, such as the conservation of chemically distinct residues in their amino acid sequences and the ability to bind fatty acids. Our results are in keeping with the lack of cellular retinoid-binding proteins in invertebrates and with their later appearance during the course of chordate evolution.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Parma, P.co Area delle Scienze 23/A, 43100 Parma, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Folli
authors.forename: Ileana
authors.initials: I
authors.lastname: Ramazzina
authors.forename: Riccardo
authors.initials: R
authors.lastname: Percudani
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Berni
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050556:Fatty Acid-Binding Proteins; D057927:Hydrophobic and Hydrophilic Interactions; D019476:Insect Proteins; D007536:Isomerism; D008024:Ligands; D018402:Manduca / Q000737:chemistry*; D008969:Molecular Sequence Data; D010802:Phylogeny; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D002352:Carrier Proteins; D050556:Fatty Acid-Binding Proteins; D019476:Insect Proteins; D008024:Ligands; D018168:Receptors, Retinoic Acid; C112910:mCRABP protein, Manduca sexta