title: Ligand Binding Induces Conformational Changes in Human Cellular Retinol-binding Protein 1 (CRBP1) Revealed by Atomic Resolution Crystal Structures.
abstract: Important in regulating the uptake, storage, and metabolism of retinoids, cellular retinol-binding protein 1 (CRBP1) is essential for trafficking vitamin A through the cytoplasm. However, the molecular details of ligand uptake and targeted release by CRBP1 remain unclear. Here we report the first structure of CRBP1 in a ligand-free form as well as ultra-high resolution structures of this protein bound to either all-trans-retinol or retinylamine, the latter a therapeutic retinoid that prevents light-induced retinal degeneration. Superpositioning of human apo- and holo-CRBP1 revealed major differences within segments surrounding the entrance to the retinoid-binding site. These included α-helix II and hairpin turns between β-strands βC-βD and βE-βF as well as several side chains, such as Phe-57, Tyr-60, and Ile-77, that change their orientations to accommodate the ligand. Additionally, we mapped hydrogen bond networks inside the retinoid-binding cavity and demonstrated their significance for the ligand affinity. Analyses of the crystallographic B-factors indicated several regions with higher backbone mobility in the apoprotein that became more rigid upon retinoid binding. This conformational flexibility of human apo-CRBP1 facilitates interaction with the ligands, whereas the more rigid holoprotein structure protects the labile retinoid moiety during vitamin A transport. These findings suggest a mechanism of induced fit upon ligand binding by mammalian cellular retinol-binding proteins.
authors.affiliation: From the Department of Pharmacology and.
authors.forename: Josie A
authors.initials: JA
authors.lastname: Silvaroli
authors.affiliation: From the Department of Pharmacology and.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Arne
authors.affiliation: From the Department of Pharmacology and the Laboratory of Hematology and Flow Cytometry, Department of Hematology, Military Institute of Medicine, Warsaw 04-141, Poland.
authors.forename: Sylwia
authors.initials: S
authors.lastname: Chelstowska
authors.affiliation: From the Department of Pharmacology and the Research Service, Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, Ohio 44106.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Kiser
authors.affiliation: the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, and the Northeastern Collaborative Access Team, Argonne National Laboratory, Argonne, Illinois 60439.
authors.forename: Surajit
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: From the Department of Pharmacology and the Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, mxg149@case.edu.
authors.forename: Marcin
authors.initials: M
authors.lastname: Golczak
mesh_terms: D018360:Crystallography, X-Ray; D006801:Humans; D006860:Hydrogen Bonding; D008024:Ligands; D017433:Protein Structure, Secondary; D054840:Retinol-Binding Proteins, Cellular / Q000737:chemistry*; D014801:Vitamin A / Q000737:chemistry*
chemical_list: D008024:Ligands; C518456:RBP1 protein, human; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A
keywords: lipid transport; retinal metabolism; retinoid-binding protein; retinol; vitamin A