title: Spectroscopic studies on the pH-dependent structural dynamics of γ-conglutin, the blood glucose-lowering protein of lupin seeds.
abstract: γ-Conglutin is a blood glucose-lowering protein purified from lupin (Lupinus albus, L.) seed. Despite various features of this protein have already been studied, no function in the seed nor any mechanism of action as a hypoglycemic nutraceutical compound have been identified so far. The lupin protein was shown to exist both in monomeric and multimeric forms as a function of pH. However, a detailed description of the pH-dependent structural dynamics of this protein, as the basis to investigate the reason/s of its functional behaviour, is not available yet. In this study, multiple and independent spectroscopic approaches, including light scattering associated to size exclusion chromatography of both untreated and covalently cross-linked protein, near and far UV circular dichroism, intrinsic and extrinsic fluorescence measurements, have been used to monitor oligomeric and conformational modifications caused by pH changes. Altogether, the results revealed a tetramer-dimer-monomer transition between neutral to slightly acidic pH and a dramatic and abrupt conformational change below pH 3.5. According to these findings, a model depicting γ-conglutin structural dynamics was drawn. This model highlights the primary role of amino acid side group electrostatic interactions in the oligomer association/dissociation equilibria and in the pH-driven collapse of the native conformation.
authors.affiliation: Department of AgriFood Molecular Sciences, Università degli Studi di Milano, Via G. Celoria 2, 20133 Milano, Italy.
authors.forename: Jessica
authors.initials: J
authors.lastname: Capraro
authors.forename: Paolo
authors.initials: P
authors.lastname: Spotti
authors.forename: Chiara
authors.initials: C
authors.lastname: Magni
authors.forename: Alessio
authors.initials: A
authors.lastname: Scarafoni
authors.forename: Marcello
authors.initials: M
authors.lastname: Duranti
mesh_terms: D001786:Blood Glucose / Q000187:drug effects*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D057927:Hydrophobic and Hydrophilic Interactions / Q000187:drug effects; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008027:Light; D010940:Plant Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D012639:Seeds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013499:Surface Properties / Q000187:drug effects; D014364:Tryptophan / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents; D010940:Plant Proteins; C079483:conglutin-gamma protein, Lupinus angustifolius; D014364:Tryptophan