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Acta Crystallogr D Biol Crystallogr. 2014 Aug;70(Pt 8):2217-31. doi: 10.1107/S1399004714011304. Epub 2014 Jul 25.

Weak protein-cationic co-ion interactions addressed by X-ray crystallography and mass spectrometry.

Author information

1
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.
2
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.
3
Institut des NanoSciences de Paris (INSP), UMR 7588 CNRS/UPMC (Université Paris 6), 4 Place Jussieu, 75252 Paris CEDEX 05, France.

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.

KEYWORDS:

ESI mass spectrometry; Hofmeister series; hen egg-white lysozyme; protein–cation interactions

PMID:
25084340
DOI:
10.1107/S1399004714011304
[Indexed for MEDLINE]

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