title: Acid-induced denaturation of cellular retinol-binding proteins types I and II studied by electrospray mass spectrometry.
abstract: The acid-induced denaturation of cellular retinol-binding proteins types I and II (CRBP I and II), in the presence and in the absence of the ligand, was studied by electrospray ionization mass spectrometry (ESI-MS) in the pH range 6.9-2.4. To avoid artifacts generated by the ESI process, suitable interface parameters were selected. Different charge-state distributions were observed in the ESI-MS spectra, reflecting the pH-dependent equilibria among protein conformations in solution. In the absence of retinol, CRBP II appeared to be more resistant than CRBP I to acid denaturation. The bound ligand stabilized both carriers, with a markedly higher effect on CRBP I. Retinol release from the ligand-bound carriers and protein denaturation occurred concomitantly. This finding suggests that the lowering of pH, reported to occur in proximity to a biomembrane, might contribute to the conformational transitions required to promote dissociation of the otherwise very stable retinal-carrier complexes and thus permit targeted delivery of vitamin A to the enzymes involved in its metabolism.
authors.affiliation: Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Università degli Studi di Parma, Parco Area delle Scienze 17/A, I-43100 Parma, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Careri
authors.forename: Lisa
authors.initials: L
authors.lastname: Elviri
authors.forename: Ingrid
authors.initials: I
authors.lastname: Zagnoni
authors.forename: Davide
authors.initials: D
authors.lastname: Cavazzini
authors.forename: Gian Luigi
authors.initials: GL
authors.lastname: Rossi
mesh_terms: D006863:Hydrogen-Ion Concentration; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D012177:Retinol-Binding Proteins / Q000032:analysis / Q000737:chemistry* / Q000145:classification*; D054840:Retinol-Binding Proteins, Cellular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014801:Vitamin A / Q000032:analysis / Q000737:chemistry*
chemical_list: D012177:Retinol-Binding Proteins; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A