Phase separation in binary eye lens protein mixtures

Dorsaz, Nicolas; Thurston, George M.; Stradner, Anna; Schurtenberger, Peter; Foffi, Giuseppe

doi:10.1039/c0sm00156b

Cited by 40 publications

(59 citation statements)

References 89 publications

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“…Interspecies interactions were shown to play a fundamental role in binary protein mixtures. Eye-lens protein systems, for example, can pass from condensation to demixing by a single point mutation, which is believed to alter the interspecies attraction (12,46). Although this selective interaction is a result of the complex structure of the proteins, research on functionalized colloids unveils unprecedented possibilities of synthesizing particles with tunable interactions.…”

Section: Resultsmentioning

confidence: 99%

“…We calculate the onset of demixing in the framework of TPT (12,24,25), a formalism well suited when fluctuations in both ϕ and c take place at the same time. We use a first-order perturbative Helmholtz free energy per particle f. To determine whether the instability is mainly driven by density or composition fluctuations, one can diagonalize the stability matrix [f] of its partial derivatives (25,26).…”

Section: Resultsmentioning

confidence: 99%

“…We choose this route because it represents an efficient way to enhance composition fluctuations and, consequently, demixing. In fact, when the interspecies attraction is reduced, the system has a strong tendency to demix (12).…”

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confidence: 99%

“…The latter have great technological importance. Colloidal gels find applications in synthetic colloid porous materials (1,2), functionalization of surfaces and films production (3,4), ceramics processing (5,6), protein assemblies (7,8), food science (9,10), and soft matter (11,12). Although they have been known for some time (13,14), it has only recently been understood that the colloidal gels arise as a result of arrested phase separation (15)(16)(17)(18).…”

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Arrested demixing opens route to bigels

Varrato

Michele

Belushkin

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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107

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Understanding and, ultimately, controlling the properties of amorphous materials is one of the key goals of material science. Among the different amorphous structures, a very important role is played by colloidal gels. It has been only recently understood that colloidal gels are the result of the interplay between phase separation and arrest. When short-ranged attractive colloids are quenched into the phase-separating region, density fluctuations are arrested and this results in ramified amorphous space-spanning structures that are capable of sustaining mechanical stress. We present a mechanism of aggregation through arrested demixing in binary colloidal mixtures, which leads to the formation of a yet unexplored class of materials--bigels. This material is obtained by tuning interspecies interactions. Using a computer model, we investigate the phase behavior and the structural properties of these bigels. We show the topological similarities and the geometrical differences between these binary, interpenetrating, arrested structures and their well-known monodisperse counterparts, colloidal gels. Our findings are supported by confocal microscopy experiments performed on mixtures of DNA-coated colloids. The mechanism of bigel formation is a generalization of arrested phase separation and is therefore universal.spinodal decomposition | DNA-coated colloids | programmable interactions | amorphous self-assembly T he properties of a self-assembled material are ultimately controlled by the interactions among its building blocks and by the conditions in which they are prepared. It is by tuning these two properties that different structures can be obtained. Shortranged attractive colloidal systems, for example, can form crystals, two glasses of different origin, or gels. The latter have great technological importance. Colloidal gels find applications in synthetic colloid porous materials (1, 2), functionalization of surfaces and films production (3, 4), ceramics processing (5, 6), protein assemblies (7, 8), food science (9, 10), and soft matter (11, 12). Although they have been known for some time (13,14), it has only recently been understood that the colloidal gels arise as a result of arrested phase separation (15-18).The gels are characterized by a ramified amorphous spacespanning structure that is capable of sustaining mechanical stress. The colloidal density plays a crucial role in the aggregation and therefore in the resulting structure. At low densities, irreversible aggregation leads to fractal gels. At intermediate densities more compact porous structures are observed, whereas a homogeneous glass emerges when the solute occupies more than 50% of the volume (11,10,14,19).It has been proven that when colloidal particles are quenched into the gas-liquid phase separation region, gelation occurs as a consequence of dynamic arrest that interferes with phase separation (15, 18). After the quench, the system is thermodynamically unstable and strong density fluctuations set in, favoring the separation of the fluid into two ...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Arrested demixing opens route to bigels

Varrato

Michele

Belushkin

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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107

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“…At the high protein concentrations of lens cytoplasm, 25-60% by weight in mammals, small changes in interprotein interactions can disrupt transparency. For human lens proteins with cataractogenic point mutations, and for high-concentration lens protein mixtures, protein interaction changes as small as a fraction of thermal energy, k B T, can induce phase separation and thus lead to opacification (3)(4)(5)(6)(7).…”

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Hard sphere-like glass transition in eye lens α-crystallin solutions

Foffi

Савин

Bucciarelli

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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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.alpha crystallin | scattering | mode-coupling theory | molecular dynamics | glass transition T he cytoplasm of the tightly packed fiber cells of the eye lens contains concentrated aqueous protein mixtures that have high refractive indexes, while normally remaining clear enough for vision. Lens clarity depends on short-range order between lens proteins (1, 2) and can be disrupted by both protein aggregation and liquid-liquid phase separation in cataract, a leading cause of blindness. At the high protein concentrations of lens cytoplasm, 25-60% by weight in mammals, small changes in interprotein interactions can disrupt transparency. For human lens proteins with cataractogenic point mutations, and for high-concentration lens protein mixtures, protein interaction changes as small as a fraction of thermal energy, k B T, can induce phase separation and thus lead to opacification (3-7).In addition to equilibrium phase transitions, dynamical transitions including glass formation and gelation can also occur at high protein concentrations like those of the eye lens (8, 9). Relatively abrupt viscoelastic changes associated with glass formation or gelation could harden the lens and contribute to presbyopia and could alter cataract formation rates by affecting aggregation and phase separation kinetics.Here we study the equilibrium liquid structure and dynamics of concentrated solutions of eye-lens α-crystallin protein solutions, using small-angle X-ray scattering (SAXS), static light scattering (SLS)...

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Multivalent ions and biomolecules: Attempting a comprehensive perspective

2020

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Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self‐organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+, to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the “atomistic/molecular” local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico‐chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.

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Phase separation in binary eye lens protein mixtures

Cited by 40 publications

References 89 publications

Arrested demixing opens route to bigels

Arrested demixing opens route to bigels

Hard sphere-like glass transition in eye lens α-crystallin solutions

Multivalent ions and biomolecules: Attempting a comprehensive perspective

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