title: Epicatechin-induced conformational changes in β-lactoglobulin B monitored by FT-IR spectroscopy.
abstract: The interaction between whey carrier protein β-lactoglobulin B and (-)-epicatechin, a major dietary flavonoid with a wide range of health-promoting biological activities, was investigated by Fourier transform infrared spectroscopy in physiological conditions. Amide I spectra of epicatechin - β-lactoglobulin complexes, in D2O buffer solutions, pD= 6.8, at molar ratios from 0.5:1 to 15:1, were measured by using a cell device specifically created. Changes in secondary structure elements at increasing epicatechin concentrations were quantified. Two different trends were observed for the intensities of β-sheet, random coil, and side chain contributions. At molar ratios ≤2 the β-exposed strand contributions (1625 cm(-1)) increased at the expence of the β-antiparallel sheet band (1637 cm(-1)). At molar ratios >2 the intensities of both β structures slightly decreased. The same behaviour was observed for the side chain contributions (band around 1610 ÷ 1620 cm(-1)). In addition, a conformational transition to a slightly opened structure, followed by aggregate formation at the highest molar ratios, were revealed. The results suggest that binding of epicatechin to β-lactoglobulin in physiological conditions occurs at the surface of the protein molecule, resulting in protein dissociation at molar ratios ≤2 with minor changes in secondary structure. This finding provides further evidence for the possibility of successful use of the protein as a carrier of flavonoids, epicatechin included.
authors.affiliation: Consiglio per la Ricerca e la sperimentazione in Agricoltura - Centro di Ricerca per gli Alimenti e la Nutrizione, Via Ardeatina 546, 00178 Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Nucara
authors.affiliation: Consiglio per la Ricerca e la sperimentazione in Agricoltura - Centro di Ricerca per gli Alimenti e la Nutrizione, Via Ardeatina 546, 00178 Rome, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Maselli
authors.affiliation: CNR-Istituto di Fotonica e Nanotecnologie, Via Cineto Romano 42, 00156 Rome, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Giliberti
authors.affiliation: Consiglio per la Ricerca e la sperimentazione in Agricoltura - Centro di Ricerca per gli Alimenti e la Nutrizione, Via Ardeatina 546, 00178 Rome, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Carbonaro
keywords: Epicatechin; FT-IR spectroscopy; Protein structure; β-lactoglobulin