| 1. |
- 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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| 2. |
- 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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