Ions in water: Characterizing the forces that control chemical processes and biological structure

Collins, Kim D.; Neilson, G. W.; Enderby, J. E.

doi:10.1016/j.bpc.2007.03.009

Cited by 589 publications

(697 citation statements)

References 65 publications

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“…Recent MD simulations suggest that ions may either bind specifically and locally to oppositely charged protein surface residues (67,68) or accumulate at nonpolar surface patches (66) as a function of type (i.e., anions/cations) and size, an observation supported by SANS experiments with varying salt concentrations and type (5,33). Moreover, both MD simulations and neutron liquid diffraction show that different ions in solution affect the local structure of water molecules (e.g., coordination numbers and orientations) specifically (69,70) so that the overall effect near protein surfaces is most probably a combination of variable local charge concentrations and, concomitantly, density variations of the water molecules with respect to the bulk solvent as a function of ion type and size (71,72). The combined SAXS/SANS data presented here quantify, in a model-free way, the local variations in electronic and neutron SLDs as a function of the character and number of amino acid residues on a protein surface.…”

Section: Protein Hs Density and Ionic Composition Depend On The Surfamentioning

confidence: 97%

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Kim

Martel

Girard

et al. 2016

Biophysical Journal

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Water molecules in the immediate vicinity of biomacromolecules, including proteins, constitute a hydration layer characterized by physicochemical properties different from those of bulk water and play a vital role in the activity and stability of these structures, as well as in intermolecular interactions. Previous studies using solution scattering, crystallography, and molecular dynamics simulations have provided valuable information about the properties of these hydration shells, including modifications in density and ionic concentration. Small-angle scattering of x-rays (SAXS) and neutrons (SANS) are particularly useful and complementary techniques to study biomacromolecular hydration shells due to their sensitivity to electronic and nuclear scattering-length density fluctuations, respectively. Although several sophisticated SAXS/SANS programs have been developed recently, the impact of physicochemical surface properties on the hydration layer remains controversial, and systematic experimental data from individual biomacromolecular systems are scarce. Here, we address the impact of physicochemical surface properties on the hydration shell by a systematic SAXS/SANS study using three mutants of a single protein, green fluorescent protein (GFP), with highly variable net charge (þ36, À6, and À29). The combined analysis of our data shows that the hydration shell is locally denser in the vicinity of acidic surface residues, whereas basic and hydrophilic/hydrophobic residues only mildly modify its density. Moreover, the data demonstrate that the density modifications result from the combined effect of residue-specific recruitment of ions from the bulk in combination with water structural rearrangements in their vicinity. Finally, we find that the specific surface-charge distributions of the different GFP mutants modulate the conformational space of flexible parts of the protein.

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Section: Protein Hs Density and Ionic Composition Depend On The Surfamentioning

confidence: 97%

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Kim

Martel

Girard

et al. 2016

Biophysical Journal

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“…[17][18][19][20][21]39 The responsiveness of PbA self-association to halogen anion identity and its relative unresponsiveness to alkali cation identity [ Fig. 4(A)] supported anion binding as being critical for selfassociation.…”

Section: Anion Binding Is Essential and Self-association Is Mediated mentioning

confidence: 99%

“…The classical view holds that such interactions are mediated indirectly through the alteration of bulk water structure, 15 although there is increasing recognition that ions interact directly with proteins. 16 Significantly, Collins has proposed [17][18][19][20][21] that ionic interactions in aqueous solution are governed by the relative affinities of ions for the molecular dipole of water. This qualitative description known as the ''Law of Matching Water Affinities'' provides a good basis for discussing interactions of dissolved salt-ions with charged protein side chains.…”

Section: Introductionmentioning

confidence: 99%

Ion‐specific modulation of protein interactions: Anion‐induced, reversible oligomerization of a fusion protein

et al. 2008

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Ions can significantly modulate the solution interactions of proteins. We aim to demonstrate that the salt-dependent reversible heptamerization of a fusion protein called peptibody A or PbA is governed by anion-specific interactions with key arginyl and lysyl residues on its peptide arms. Peptibody A, an E. coli expressed, basic (pI 5 8.8), homodimer (65.2 kDa), consisted of an IgG1-Fc with two, C-terminal peptide arms linked via penta-glycine linkers. Each peptide arm was composed of two, tandem, active sequences (SEYQGL PPQGWK) separated by a spacer (GSGSATGGSGGGASSGSGSATG). PbA was monomeric in 10 mM acetate, pH 5.0 but exhibited reversible self-association upon salt addition. The sedimentation coefficient (s w ) and hydrodynamic diameter (D H ) versus PbA concentration isotherms in the presence of 140 mM NaCl (A5N) displayed sharp increases in s w and D H , reaching plateau values of 9 s and 16 nm by 10 mg/mL PbA. The D H and sedimentation equilibrium data in the plateau region (>12 mg/mL) indicated the oligomeric ensemble to be monodisperse (PdI 5 0.05) with a z-average molecular weight (M z ) of 433 kDa (stoichiometry 5 7). There was no evidence of reversible selfassociation for an IgG1-Fc molecule in A5N by itself or in a mixture containing fluorescently labeled IgG1-Fc and PbA, indicative of PbA self-assembly being mediated through its peptide arms. Self-association increased with pH, NaCl concentration, and anion size (I 2 > Br 2 > Cl 2 > F 2 ) but could be inhibited using soluble Trp-, Phe-, and Leu-amide salts (Trp > Phe > Leu). We propose that in the presence of salt (i) anion binding renders PbA self-association competent by neutralizing the peptidyl arginyl and lysyl amines, (ii) self-association occurs via aromatic and hydrophobic interactions between the ..xx ..xxx.. xx.. motifs, and (iii) at >10 mg/mL, PbA predominantly exists as heptameric clusters.Keywords: Hofmeister series; electroselectivity series; self-association; ion-protein interactions; anion binding; dynamic light scattering; analytical ultracentrifugation Abbreviations: A5, 10 mM acetate buffer at pH 5.0; A5N, 10 mM acetate buffer at pH 5.0 containing 140 mM sodium chloride;

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“…To disclose the mechanism of electrolyte impact on biological functions it is necessary to study their interaction with water, proteins and with each other in liquid media. This problem has been intensively studied and discussed for more than 120 years [2][3][4][5][6][7][8][9][10][11][12]. At the beginning of this paper, I would like to consider in breath some basic achievements, which are helpful for understanding water-ion-interface interactions during drying of sessile drops.…”

Section: Introductionmentioning

confidence: 99%

“…It is worthy of notice that, according to the data of neutron and X-ray scattering [6], as well as of gel-chromatography [8], univalent ions attract only one layer of hydrated water molecules, and bivalent ions two layers. Thus, existence of multilayer hydrated shells due to electrostatic attraction forces is doubted by some authors [10]. Of particular importance are studies of ion distribution in aqueous phase and their interaction with different surfaces, specifically with the surface at the water-air interface.…”

Section: Introductionmentioning

confidence: 99%

Surface Properties of Vitally Important Ions: Sessile Desiccated Drop Studies

Yakhno¹

2012

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Surface properties of ions in a liquid media are the most important and interesting topic of physical-chemical research. Complex approaches with using a lot of modern equipment are used for study this problem. Here we demonstrate a distinctive method, which is based on self-organizing processes in sessile desiccative drops of water salt solutions. The features of crystallization of aqueous solutions of KCl, NaCl, CaCl 2 and MgCl 2 , as well as of their mixtures drying in the form of drops (3 ul) on glass have been studied by optical microscopy and acoustic impedancemetry. "Dynamic portraits" of crystallization kinetics (KCl, NaCl and their mixture) or of saline condensation (CaCl 2 and MgCl 2 ) in the course of drop drying have been obtained for each sample. The phenomenon of drop fragmentation of a mixture of potassium-containing solutions of various chlorides and formation of individual 3D structures on the glass has been revealed. The mechanisms of formation of such structures associated with different surface activity of the studied ions are considered. It is demonstrated that the used approaches are promising for obtaining additional information about complex behavior of ions in aqueous media.

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Ions in water: Characterizing the forces that control chemical processes and biological structure

Cited by 589 publications

References 65 publications

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Ion‐specific modulation of protein interactions: Anion‐induced, reversible oligomerization of a fusion protein

Surface Properties of Vitally Important Ions: Sessile Desiccated Drop Studies

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