Diffusivities of Lysozyme in Aqueous MgCl<sub>2</sub> Solutions from Dynamic Light-Scattering Data:  Effect of Protein and Salt Concentrations

Grigsby, J.J.; Blanch, Harvey W.; Prausnitz, John M.

doi:10.1021/jp993177s

Cited by 52 publications

(52 citation statements)

References 41 publications

(92 reference statements)

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“…Upon a further increase in the ionic strength, the attraction reaches an extremum and then gradually decreases. The minimum in the interprotein potential of mean force as a function of ionic strength is consistent with the nonmonotonic salt effects observed in measurements of cloud temperatures in lysozyme solutions, 35-37 diffusion coefficients of lysozyme and concanavalin, 37,38 activity of lactoglobulin, 39 and association equilibria in insulin solutions. 40 Clearly, other important phenomena, such as van der Waals and hydrophobic interactions 1,19 and isotropic Coulombic effects [41][42][43] observed in multivalent salts, can contribute to interprotein attraction, shifting the observed 35-40 extrema toward higher salt concentrations.…”

Section: Resultssupporting

confidence: 79%

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Bratko

Striolo

et al. 2002

J. Phys. Chem. B

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Potentials of mean force between nonuniformly charged colloids or globular proteins are often estimated as a pairwise sum of distinct orientation averages for charge-dipole and dipole-dipole interactions. In systems with dipole-related interactions comparable to or exceeding the thermal energy, however, correlations between charge-dipole and dipole-dipole terms can render the additivity assumption highly inaccurate. On the basis of the third-order cumulant expansion of intercolloidal interactions, we derive an asymptotically exact relation for the potential of mean force that includes the correlation between distinct contributions. Using a simple discrete-orientation model, we obtain an approximate expression for the nonadditivity correction that reproduces correct behavior in weak and strong coupling limits and is sufficiently accurate for practical calculations over a wide range of interaction strengths including those characteristic of aqueous protein solutions.

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Section: Resultssupporting

confidence: 79%

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Bratko

Striolo

et al. 2002

J. Phys. Chem. B

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“…Another contribution to the value of ∆Z at high ionic strengths may be variations in hydrodynamic radius with ionic strength. Grigsby et al 33 estimated the hydrodynamic radius of lysozyme using dynamic light scattering while changing the ionic strength of the buffer and found no clear trend. The observed changes in the value of the radius were attributed to the changes in hydration layer and to the binding of ions at the surface of the protein.…”

Section: Influence Of the Hydrodynamic Radiusmentioning

confidence: 99%

Significance of Charge Regulation in the Analysis of Protein Charge Ladders

2003

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Analysis of protein charge ladders using capillary electrophoresis (CE) provides a method of determining charges of proteins. This method has disregarded the effect of charge compensationsa response of the protein and its environment to a change in electrostatic potential on the surface of the protein. This work examines the difference in charge, ∆Z, between the first two rungs of the ladder of bovine carbonic anhydrase II (BCAII) as a function of pH and ionic strength using CE. These data were analyzed in three ways: using models based on Hückel theory and on charge regulation, and using linear regression. These analyses were in only qualitative agreement, and the differences between them suggest that simple theoretical models for the behavior of colloidal particles cannot establish the value of ∆Z accurately in proteins. Linear regression of mobilities of the rungs of charge ladderssa method proposed in earlier workscontinues to be a computationally convenient method of estimating the charge Z 0 of native proteins, but the accuracy of this method depends on the value of ∆Z. The absolute value of ∆Z cannot presently be established accurately. In the case of BCAII, we suggest ∆Z ) -0.93 for the difference in charge between the first two rungs of the charge ladder at pH ) 8.4 and 10 mM ionic strength. An estimate of the uncertainty in this value for BCAII due to uncertainties in the values of pK a of amino acids and of the hydrodynamic radius is (0.02. Other uncertainties not considered in this analysis will make this value larger. IntroductionA protein charge ladder is a collection of derivatives of a protein generated by converting its charged groups (most commonly lysine -NH 3 + but also aspartate or glutamate -CO 2 -) into electrically neutral ones ( -NHCOCH 3 or -CO 2 CH 3 ). 1 In free solution capillary electrophoresis (CE), these modified proteins separate into distinct peaks or "rungs"; each rung contains regioisomers with approximately the same charge: that is, at least nominally, the same number of modified groups. Charge ladders provide a self-calibrating tool for estimating certain basic physical parameters of proteins such as charge, 2,3 hydrodynamic radius, 4 and electrostatic contributions to the free energy of binding of ligands 5,6 and of protein folding. 7 The simplest analysis of charge ladders assumes that the charge difference (∆Z) between the consecutive rungs of a charge ladder generated by acetylation of lysine -NH 3 + groups is a full unit of charge (∆Z ) -1). Menon and Zydney have made the point that ∆Z may have a value different from -1 if the change in charge of the -amino group on acetylation (which is, in fact, -1, provided that this group is completely protonated before acetylation) is offset by a compensating change in charge elsewhere in the protein. 8 This conceptscharge compensations is well-developed and extensively modeled in colloid chemistry. 9,10 Menon and Zydney suggested that it also applies to proteins and proposed a model to analyze the adjustment of charge of the macro...

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“…37 Examination of D 12 . Values of (D 12 ) V for the lysozymeCaCl 2 and lysozyme-MgCl 2 systems are shown in Figure 1b.…”

Section: Discussionmentioning

confidence: 99%

Multicomponent Diffusion of Lysozyme in Aqueous Calcium Chloride. The Role of Common-Ion Effects and Protein−Salt Preferential Interactions

2007

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To investigate the effect of calcium salts on the thermodynamic and transport properties of aqueous solutions of proteins, we report ternary diffusion coefficients for the lysozyme-CaCl 2 -water ternary system at 25°C and pH 4.5. We have used our ternary diffusion coefficients to calculate preferential-interaction coefficients as a function of salt concentration. This has allowed us to characterize protein-salt thermodynamic interactions. We have observed the presence of large common-ion effects by examining the dependence of the diffusion coefficients on salt concentration. Our results are compared to those previously reported for the lysozymeMgCl 2 -water ternary system. We have found that the common-ion effect is essentially the same for both salt cases. On the other hand, by examining the dependence of the preferential-interaction coefficient on salt concentration, we have found that salt preferentially interacts with the protein in the lysozyme-CaCl 2 -water system, whereas water preferentially interacts with the protein in lysozyme-MgCl 2 -water system. This is consistent with the known generally larger affinity of Mg 2+ for water, as compared to Ca 2+, and the different roles that these two divalent metal ions play in biochemical processes. We remark that neglecting the common-ion contribution of the preferential-interaction coefficient can lead to qualitatively inaccurate descriptions of protein-salt aqueous systems, even at high salt concentrations. Indeed, for the lysozymeCaCl 2 system, this approximation would lead to interpretations inconsistent with the known destabilizing effect of calcium ions on proteins.

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Diffusivities of Lysozyme in Aqueous MgCl₂ Solutions from Dynamic Light-Scattering Data: Effect of Protein and Salt Concentrations

Cited by 52 publications

References 41 publications

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Significance of Charge Regulation in the Analysis of Protein Charge Ladders

Multicomponent Diffusion of Lysozyme in Aqueous Calcium Chloride. The Role of Common-Ion Effects and Protein−Salt Preferential Interactions

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Diffusivities of Lysozyme in Aqueous MgCl2 Solutions from Dynamic Light-Scattering Data: Effect of Protein and Salt Concentrations

Cited by 52 publications

References 41 publications

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Orientation-Averaged Pair Potentials between Dipolar Proteins or Colloids

Significance of Charge Regulation in the Analysis of Protein Charge Ladders

Multicomponent Diffusion of Lysozyme in Aqueous Calcium Chloride. The Role of Common-Ion Effects and Protein−Salt Preferential Interactions

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Product

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Diffusivities of Lysozyme in Aqueous MgCl₂ Solutions from Dynamic Light-Scattering Data: Effect of Protein and Salt Concentrations