title: Weak protein-cationic co-ion interactions addressed by X-ray crystallography and mass spectrometry.
abstract: The adsorption of Rb(+), Cs(+), Mn(2+), Co(2+) and Yb(3+) onto the positively charged hen egg-white lysozyme (HEWL) has been investigated by solving 13 X-ray structures of HEWL crystallized with their chlorides and by applying electrospray ionization mass spectrometry (ESI-MS) first to dissolved protein crystals and then to the protein in buffered salt solutions. The number of bound cations follows the order Cs(+) < Mn(2+) ≃ Co(2+) < Yb(3+) at 293 K. HEWL binds less Rb(+) (qtot = 0.7) than Cs(+) (qtot = 3.9) at 100 K. Crystal flash-cooling drastically increases the binding of Cs(+), but poorly affects that of Yb(3+), suggesting different interactions. The addition of glycerol increases the number of bound Yb(3+) cations, but only slightly increases that of Rb(+). HEWL titrations with the same chlorides, followed by ESI-MS analysis, show that only about 10% of HEWL binds Cs(+) and about 40% binds 1-2 Yb(3+) cations, while the highest binding reaches 60-70% for protein binding 1-3 Mn(2+) or Co(2+) cations. The binding sites identified by X-ray crystallography show that the monovalent Rb(+) and Cs(+) preferentially bind to carbonyl groups, whereas the multivalent Mn(2+), Co(2+) and Yb(3+) interact with carboxylic groups. This work elucidates the basis of the effect of the Hofmeister cation series on protein solubility.
authors.affiliation: Laboratoire de Cristallographie et RMN Biologiques, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris Descartes, UMR 8015 CNRS, 4 Avenue de l'Observatoire, 75270 Paris CEDEX 06, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Bénas
authors.affiliation: Laboratoire de Chimie-Toxicologie Analytique et Cellulaire EA 4463, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris Descartes, 4 Avenue de l'Observatoire, 75270 Paris CEDEX 06, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Auzeil
authors.affiliation: Institut des NanoSciences de Paris (INSP), UMR 7588 CNRS/UPMC (Université Paris 6), 4 Place Jussieu, 75252 Paris CEDEX 05, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Legrand
authors.affiliation: Laboratoire de Cristallographie et RMN Biologiques, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris Descartes, UMR 8015 CNRS, 4 Avenue de l'Observatoire, 75270 Paris CEDEX 06, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Brachet
authors.affiliation: Laboratoire de Chimie-Toxicologie Analytique et Cellulaire EA 4463, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris Descartes, 4 Avenue de l'Observatoire, 75270 Paris CEDEX 06, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Regazzetti
authors.affiliation: Laboratoire de Cristallographie et RMN Biologiques, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris Descartes, UMR 8015 CNRS, 4 Avenue de l'Observatoire, 75270 Paris CEDEX 06, France.
authors.forename: Madeleine
authors.initials: M
authors.lastname: Riès-Kautt
mesh_terms: D000327:Adsorption; D002412:Cations; D018360:Crystallography, X-Ray / Q000379:methods*; D011506:Proteins / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D002412:Cations; D011506:Proteins
keywords: ESI mass spectrometry; Hofmeister series; hen egg-white lysozyme; protein–cation interactions