title: Unfolding of beta-lactoglobulin on the surface of polystyrene nanoparticles: experimental and computational approaches.
abstract: Structural changes ensuing from the non-covalent absorption of bovine beta-lactoglobulin (BLG) on the surface of polystyrene nanoparticles were investigated by using spectroscopic approaches, by assessing the reactivity of specific residues, and by limited proteolysis/mass spectrometry. Also, the immunoreactivity of absorbed and free BLG was compared. All these approaches indicated substantial rearrangements of the protein structure in the absorbed state, in spite of the reported structural rigidity of BLG. Changes made evident by experimental measurements were confirmed by computational approaches. These indicate that adsorption-related changes are most marked in the area between the main C-terminal alpha helix and the beta-barrel, and lead to full exposure of the thiol on Cys121 , consistent with experimental measurements. In the computational model of bound BLG, both Trp61 and Trp19 also move away from their neighboring quenchers and become solvent-exposed, as indicated by fluorescence measurement. Upon binding, the beta-barrel also loosens, with a substantial increase in immunoreactivity and with noticeable changes in the trypsinolytic pattern. The possible general significance of the structural changes reported here for non-covalently adsorbed BLG is discussed with respect to recognition events involving surface-bound proteins, as are aspects related to the carrier function(s) of BLG, and to its use as a common ingredient in many food systems.
authors: Section of Chemistry and Biomolecular Sciences, DeFENS, University of Milan, Via Celoria 2, 20133, Milan, Italy.
authors: Matteo
authors: M
authors: Miriani
authors: Ivano
authors: I
authors: Eberini
authors: Stefania
authors: S
authors: Iametti
authors: Pasquale
authors: P
authors: Ferranti
authors: Cristina
authors: C
authors: Sensi
authors: Francesco
authors: F
authors: Bonomi
mesh_terms: D000818:Animals; D002417:Cattle; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D058767:Protein Unfolding; D013050:Spectrometry, Fluorescence
chemical_list: D007782:Lactoglobulins; D011137:Polystyrenes
keywords: beta-lactoglobulin; molecular dynamics; polystyrene nanoparticles; protein unfolding; solid-liquid interfaces