title: Nuclear magnetic resonance study of the conformation and dynamics of beta-casein at the oil/water interface in emulsions.
abstract: A (13)C and (31)P nuclear magnetic resonance (NMR) study has been carried out on beta-casein adsorbed at the interface of a tetradecane/water emulsion. (13)C NMR spectra show signals from the carbonyl, carboxyl, aromatic, and C alpha carbons in beta-casein, well resolved from solvent resonances. Only a small fraction of all carbon atoms in beta-casein contribute to detectable signals; intensity measurements show that the observable spectrum is derived from about 30 to 40 amino acid residues.(31)P NMR spectra show signals from the five phosphoserines on the hydrophilic N-terminal part of the protein. Analysis of T(1) relaxation times of these nuclei, using the model free approach for the spectral density function and the line shape of the alpha-carbon region, indicates that a large part of the protein is in a random coil conformation with restricted motion and a relatively long internal correlation time. The NMR results show that the conformation and dynamics of the N-terminal part of beta-casein are not strongly altered at the oil/water interface, as compared to beta-casein in micelle-like aggregates in aqueous solution.
authors.affiliation: Department of Molecular Physics, Wageningen Agricultural University, The Netherlands.
authors.forename: L C
authors.initials: LC
authors.lastname: ter Beek
authors.forename: M
authors.initials: M
authors.lastname: Ketelaars
authors.forename: D C
authors.initials: DC
authors.lastname: McCain
authors.forename: P E
authors.initials: PE
authors.lastname: Smulders
authors.forename: P
authors.initials: P
authors.lastname: Walstra
authors.forename: M A
authors.initials: MA
authors.lastname: Hemminga
mesh_terms: D000327:Adsorption; D000473:Alkanes; D000818:Animals; D002247:Carbon Isotopes; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D004655:Emulsions; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009821:Oils; D010758:Phosphorus; D010768:Phosphoserine / Q000032:analysis; D011487:Protein Conformation; D014867:Water
chemical_list: D000473:Alkanes; D002247:Carbon Isotopes; D002364:Caseins; D004655:Emulsions; D009821:Oils; C024713:n-tetradecane; D014867:Water; D010768:Phosphoserine; D010758:Phosphorus