title: Carboxylate Ion Pairing with Alkali-Metal Ions for β-Lactoglobulin and Its Role on Aggregation and Interfacial Adsorption.
abstract: We report a combined experimental and computational study of the whey protein β-lactoglobulin (BLG) in different electrolyte solutions. Vibrational sum-frequency generation (SFG) and ellipsometry were used to investigate the molecular structure of BLG modified air-water interfaces as a function of LiCl, NaCl, and KCl concentrations. Molecular dynamics (MD) simulations and thermodynamic integration provided details of the ion pairing of protein surface residues with alkali-metal cations. Our results at pH 6.2 indicate that BLG at the air-water interface forms mono- and bilayers preferably at low and high ionic strength, respectively. Results from SFG spectroscopy and ellipsometry are consistent with intimate ion pairing of alkali-metal cations with aspartate and glutamate carboxylates, which is shown to be more effective for smaller cations (Li(+) and Na(+)). MD simulations show not only carboxylate-alkali-metal ion pairs but also ion multiplets with the alkali-metal ion in a bridging position between two or more carboxylates. Consequently, alkali-metal cations can bridge carboxylates not only within a monomer but also between monomers, thus providing an important dimerization mechanism between hydrophilic surface patches.
authors.affiliation: †Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 25, 91052 Erlangen, Germany.|‡Cluster of Excellence Engineering of Advanced Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen, Germany.
authors.forename: Frank R
authors.initials: FR
authors.lastname: Beierlein
authors.affiliation: †Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 25, 91052 Erlangen, Germany.|‡Cluster of Excellence Engineering of Advanced Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen, Germany.|∥Centre for Molecular Design, University of Portsmouth, King Henry Building, King Henry I Street, Portsmouth PO1 2DY, United Kingdom.
authors.forename: Timothy
authors.initials: T
authors.lastname: Clark
authors.affiliation: ‡Cluster of Excellence Engineering of Advanced Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen, Germany.|§Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstraße 4, 91058 Erlangen, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Braunschweig
authors.affiliation: §Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstraße 4, 91058 Erlangen, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Engelhardt
authors.affiliation: §Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstraße 4, 91058 Erlangen, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Glas
authors.affiliation: ‡Cluster of Excellence Engineering of Advanced Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen, Germany.|§Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstraße 4, 91058 Erlangen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Peukert
mesh_terms: D000327:Adsorption; D002264:Carboxylic Acids / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry*; D008672:Metals, Alkali / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D009942:Organometallic Compounds / Q000737:chemistry* / Q000494:pharmacology*; D055503:Protein Multimerization / Q000187:drug effects*; D020836:Protein Structure, Quaternary; D013816:Thermodynamics
chemical_list: D002264:Carboxylic Acids; D007782:Lactoglobulins; D008672:Metals, Alkali; D009942:Organometallic Compounds