title: Structure and backbone dynamics of Apo- and holo-cellular retinol-binding protein in solution.
abstract: Retinoid-binding proteins play an important role in regulating transport, storage, and metabolism of vitamin A and its derivatives. The solution structure and backbone dynamics of rat cellular retinol-binding protein type I (CRBP) in the apo- and holo-form have been determined and compared using multidimensional high resolution NMR spectroscopy. The global fold of the protein is consistent with the common motif described for members of the intracellular lipid-binding protein family. The most relevant difference between the NMR structure ensembles of apo- and holoCRBP is the higher backbone disorder, in the ligand-free form, of some segments that frame the putative entrance to the ligand-binding site. These comprise alpha-helix II, the subsequent linker to beta-strand B, the hairpin turn between beta-strands C and D, and the betaE-betaF turn. The internal backbone dynamics, obtained from 15N relaxation data (T1, T2, and heteronuclear nuclear Overhauser effect) at two different fields, indicate several regions with significantly higher backbone mobility in the apoprotein, including the betaC-betaD and betaE-betaF turns. Although apoCRBP contains a binding cavity more shielded than that of any other retinoid carrier, conformational flexibility in the portal region may assist retinol uptake. The stiffening of the backbone in the holoprotein guarantees the stability of the complex during retinol transport and suggests that targeted retinol release requires a transiently open state that is likely to be promoted by the acceptor or the local environment.
authors.affiliation: Department of Experimental Medicine, Section of Chemistry and Structural Biochemistry, University of Parma, 43100 Parma, Italy.
authors.forename: Lorella
authors.initials: L
authors.lastname: Franzoni
authors.forename: Christian
authors.initials: C
authors.lastname: Lücke
authors.forename: Carlos
authors.initials: C
authors.lastname: Pérez
authors.forename: Davide
authors.initials: D
authors.lastname: Cavazzini
authors.forename: Martin
authors.initials: M
authors.lastname: Rademacher
authors.forename: Christian
authors.initials: C
authors.lastname: Ludwig
authors.forename: Alberto
authors.initials: A
authors.lastname: Spisni
authors.forename: Gian Luigi
authors.initials: GL
authors.lastname: Rossi
authors.forename: Heinz
authors.initials: H
authors.lastname: Rüterjans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D018076:DNA, Complementary / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D012177:Retinol-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A / Q000737:chemistry / Q000493:pharmacokinetics
chemical_list: D018076:DNA, Complementary; D008024:Ligands; D008055:Lipids; C518458:Rbp1 protein, rat; D012177:Retinol-Binding Proteins; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A