| 1. |
- Bergman, Maxime J., et al.
(författare)
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Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:10, s. 2432-2438
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Tidskriftsartikel (refereegranskat)abstract
- Lysozyme is known to form equilibrium clusters at pH ≈ 7.8 and at low ionic strength as a result of a mixed potential. While this cluster formation and the related dynamic and static structure factors have been extensively investigated, its consequences on the macroscopic dynamic behavior expressed by the zero shear viscosity η 0 remain controversial. Here we present results from a systematic investigation of η 0 using two complementary passive microrheology techniques, dynamic light scattering based tracer microrheology, and multiple particle tracking using confocal microscopy. The combination of these techniques with a simple but effective evaporation approach allows for reaching concentrations close to and above the arrest transition in a controlled and gentle way. We find a strong increase of η 0 with increasing volume fraction φ with an apparent divergence at φ ≈ 0.35, and unambiguously demonstrate that this is due to the existence of an arrest transition where a cluster glass forms. These findings demonstrate the power of tracer microrheology to investigate complex fluids, where weak temporary bonds and limited sample volumes make measurements with classical rheology challenging.
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| 2. |
- Bucciarelli, Saskia, et al.
(författare)
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Dramatic influence of patchy attractions on short-time protein diffusion under crowded conditions
- 2016
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 2:12, s. 1601432-1601432
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Tidskriftsartikel (refereegranskat)abstract
- In the dense and crowded environment of the cell cytoplasm, an individual protein feels the presence of and interacts with all surrounding proteins. While we expect this to strongly influence the short-time diffusion coefficient Ds of proteins on length scales comparable to the nearest-neighbor distance, this quantity is difficult to assess experimentally. We demonstrate that quantitative information about Ds can be obtained from quasi-elastic neutron scattering experiments using the neutron spin echo technique. We choose two well-characterized and highly stable eye lens proteins, bovine α-crystallin and γB-crystallin, and measure their diffusion at concentrations comparable to those present in the eye lens. While diffusion slows down with increasing concentration for both proteins, we find marked variations that are directly linked to subtle differences in their interaction potentials. A comparison with computer simulations shows that anisotropic and patchy interactions play an essential role in determining the local short-time dynamics. Hence, our study clearly demonstrates the enormous effect that weak attractions can have on the short-time diffusion of proteins at concentrations comparable to those in the cellular cytosol.
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| 3. |
- BUCCIARELLI, SASKIA, et al.
(författare)
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Extended Law of Corresponding States Applied to Solvent Isotope Effect on a Globular Protein
- 2016
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 7:9, s. 1610-1615
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Tidskriftsartikel (refereegranskat)abstract
- Investigating proteins with techniques such as NMR or neutron scattering frequently requires the partial or complete substitution of D2O for H2O as a solvent, often tacitly assuming that such a solvent substitution does not significantly alter the properties of the protein. Here, we report a systematic investigation of the solvent isotope effect on the phase diagram of the lens protein gamma B-crystallin in aqueous solution as a model system exhibiting liquid-liquid phase separation. We demonstrate that the observed strong variation of the critical temperature T-c can be described by the extended law of corresponding states for all H2O/D2O ratios, where scaling of the temperature by T-c or the reduced second virial coefficient accurately reproduces the binodal, spinodal, and osmotic compressibility. These findings highlight the impact of H2O/D2O substitution on gamma B-crystallin properties and warrant further investigations into the universality of this phenomenon and its underlying mechanisms.
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| 4. |
- Bucciarelli, Saskia, et al.
(författare)
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Unusual dynamics of concentration fluctuations in solutions of weakly attractive globular proteins
- 2015
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1089-5639. ; 6:22, s. 4470-4474
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Tidskriftsartikel (refereegranskat)abstract
- The globular protein γB-crystallin exhibits a complex phase behavior, where liquid–liquid phase separation characterized by a critical volume fraction ϕc = 0.154 and a critical temperature Tc = 291.8 K coexists with dynamical arrest on all length scales at volume fractions around ϕ ≈ 0.3–0.35, and an arrest line that extends well into the unstable region below the spinodal. However, although the static properties such as the osmotic compressibility and the static correlation length are in quantitative agreement with predictions for binary liquid mixtures, this is not the case for the dynamics of concentration fluctuations described by the dynamic structure factor S(q,t). Using a combination of dynamic light scattering and neutron spin echo measurements, we demonstrate that the competition between critical slowing down and dynamical arrest results in a much more complex wave vector dependence of S(q,t) than previously anticipated.
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| 5. |
- Cardinaux, Frederic, et al.
(författare)
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Cluster-Driven Dynamical Arrest in Concentrated Lysozyme Solutions
- 2011
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:22, s. 7227-7237
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed experimental and numerical study of the structural and dynamical properties of salt-free lysozyme solutions. In particular, by combining small-angle X-ray scattering (SAXS) data with neutron spin echo (NSE) and rheology experiments, we are able to identify that an arrest transition takes place at intermediate densities, driven by the slowing down of the cluster motion. Using an effective pair potential among proteins, based on the combination of short-range attraction and long-range repulsion, we account remarkably well for the peculiar volume fraction dependence of the effective structure factor measured by SAXS. We show that a transition from a monomer to a cluster-dominated fluid happens at volume fractions larger than phi greater than or similar to 0.05 where the close agreement between NSE measurements and Brownian dynamics simulations confirms the transient nature of the clusters. Clusters even stay transient above the geometric percolation found in simulation at phi > 0.15, though NSE reveals a cluster lifetime that becomes increasingly large and indicates a divergence of the diffusivity at phi greater than or similar to 0.26. Macroscopic measurements of the viscosity confirm this transition where the long-lived-nature of the clusters is at the origin of the simultaneous dynamical arrest at all length scales.
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| 6. |
- Chushkin, Yuriy, et al.
(författare)
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Probing Cage Relaxation in Concentrated Protein Solutions by X-Ray Photon Correlation Spectroscopy
- 2022
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of proteins on length scales of their size is crucial for understanding the machinery of living cells. X-ray photon correlation spectroscopy (XPCS) is currently the only way to access long-time collective diffusion on these length scales, but radiation damage so far limits the use in biological systems. We apply a new approach to use XPCS to measure cage relaxation in crowded α-crystallin solutions. This allows us to correct for radiation effects, obtain missing information on long time diffusion, and support the fundamental analogy between protein and colloid dynamical arrest.
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| 7. |
- Chushkin, Yuriy, et al.
(författare)
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Probing Cage Relaxation in Concentrated Protein Solutions by X-Ray Photon Correlation Spectroscopy
- 2022
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Ingår i: Physical Review Letters. - 0031-9007. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of proteins on length scales of their size is crucial for understanding the machinery of living cells. X-ray photon correlation spectroscopy (XPCS) is currently the only way to access long-time collective diffusion on these length scales, but radiation damage so far limits the use in biological systems. We apply a new approach to use XPCS to measure cage relaxation in crowded α-crystallin solutions. This allows us to correct for radiation effects, obtain missing information on long time diffusion, and support the fundamental analogy between protein and colloid dynamical arrest.
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| 8. |
- Dorsaz, Nicolas, et al.
(författare)
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Phase separation in binary eye lens protein mixtures
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:5, s. 1763-1776
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Tidskriftsartikel (refereegranskat)abstract
- Liquid-liquid phase separation occurs in young mammalian eye lenses and in concentrated solutions of isolated eye lens proteins, and has been linked to some forms of cataract. Here we study theoretically the protein compositions and cloud temperatures of two separated equilibrium phases that form out of concentrated mixtures of model proteins, chosen to have properties similar to those which reproduce experimental data on mixtures of two of the prevalent mammalian eye lens proteins, gamma- and alpha-crystallin. We use a thermodynamic perturbation theory that has previously been shown to provide a quantitative model for key features of the experimentally observed neutron scattering, phase boundary and tie line data, and that is also consistent with corresponding model, coarse-grained molecular dynamics simulations. In so doing we find an extremely sensitive dependence of protein partitioning on mutual attraction that is likely to have implications for many other protein, colloid, and other soft condensed matter systems. Previously, we found that a model square well attraction between the proteins of well depth u(alpha gamma) approximate to 0.5 k(B)T protects concentrated gamma-alpha mixtures against thermodynamic instability and is thus essential for their transparency. Furthermore, the dependence of the mixture phase separation on u(alpha gamma) was found to be highly non-monotonic, in that either weakening or increasing u(alpha gamma) by 0.5 k(B)T can lead to considerably enhanced phase separation that occurs at much higher temperatures. In the present work we show that the compositions of the separated protein phases are even more dramatically sensitive to the magnitude of u(alpha gamma). Specifically, increasing u(alpha gamma) by just 0.2 k(B)T can change the phase separation of alpha-gamma mixtures from one that is primarily compositional in nature to one of protein density separation, in which the two phases in equilibrium differ principally in overall protein concentration. Further, for the square-well widths investigated, we find that the phase separation properties change relatively rapidly in response to changes in square well depth, in comparison with their response to changes in the diameter ratio of the model proteins. We discuss potential ways in which sensitive connections between changes in molecular attraction and their macroscopic consequences, a hallmark of concentrated liquid mixtures, can lead to potential molecular mechanisms for hereditary and other forms of cataract, and can be applied to other colloidal and physiological systems.
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| 9. |
- Foffi, Giuseppe, et al.
(författare)
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Hard sphere-like glass transition in eye lens α-crystallin solutions.
- 2014
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 111:47, s. 16748-16753
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Tidskriftsartikel (refereegranskat)abstract
- We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus-Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis.
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| 10. |
- Garting, Tommy, et al.
(författare)
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Optical Microrheology of Protein Solutions Using Tailored Nanoparticles
- 2018
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Ingår i: Small. - : Wiley. - 1613-6810.
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Tidskriftsartikel (refereegranskat)abstract
- This work represents a critical re-examination of the application of dynamic light scattering (DLS)–based tracer particle microrheology to measure the zero shear viscosity of aqueous solutions of different proteins up to very high concentrations. It is demonstrated that a combination of surface-functionalized tracer particles, the use of the so-called 3D-DLS technique, and carefully chosen parameters for the scattering experiments is essential for a reliable and artifact-free determination of the viscosity of highly diverse protein solutions, while keeping the amount of protein to a minimum. The major challenges that arise in such microrheology experiments with protein solutions are discussed and used as guiding principles for the synthesis of all-purpose tracer particles with optimal size and an efficient surface functionalization, and the choice of the appropriate amount of tracers in the sample. Potential problems arising from depletion attractions between the tracer particles induced by the proteins are addressed, and compelling evidences for the absence of such effects are presented. The validity of the approach is corroborated by the perfect agreement between the zero shear viscosity obtained from 3D-DLS-based microrheology and literature data from classical rheological measurements for two vastly different protein–solvent systems up to concentrations close to the arrest transition.
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