| 11. |
- Garting, Tommy, et al.
(författare)
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Synthesis and application of PEGylated tracer particles for measuring protein solution viscosities using Dynamic Light Scattering-based microrheology
- 2019
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 181, s. 516-523
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of flow properties, such as the zero shear viscosity, of protein solutions is of paramount importance for many applications such as pharmaceutical formulations, where the syringeability of physiologically effective doses is a key property. However, the determination of these properties with classical rheological methods is often challenging due to e.g. detrimental surface effects or simply the lack of sufficient material. A possible alternative is Dynamic Light Scattering-based microrheology, where the Brownian motion of tracer particles embedded in the protein solution is monitored to access the zero shear viscosity of the sample. The prime advantages of this method compared to classical rheology are the absence of disturbing surface effects and the up to two orders of magnitude smaller protein quantities needed for an entire concentration series. This Protocol provides a detailed description of the synthesis of sterically stabilized tracer particles with surface and overall particle properties specifically designed to investigate the viscosity of protein solutions up to concentrations close to the arrest transition. These particles are tailored to avoid protein-particle as well as particle-particle aggregation at various sample conditions and thus allow for an artifact-free application of Dynamic Light Scattering-based tracer microrheology to determine the flow behaviour of biological samples. The Protocol concludes with step by step instructions for the characterization of protein solutions using a combination of the tracer particles and an advanced dynamic light scattering technique yielding the concentration-dependent zero shear viscosity.
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| 12. |
- Gaspar, Ricardo, et al.
(författare)
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Eye lens crystallin proteins inhibit the autocatalytic amyloid amplification nature of mature α-synuclein fibrils
- 2020
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- Parkinson´s disease is characterized by the accumulation of proteinaceous aggregates in Lewy bodies and Lewy Neurites. The main component found in such aggregates is α-synuclein. Here, we investigate how bovine eye lens crystallin proteins influence the aggregation kinetics of α-synuclein at mildly acidic pH (5.5) where the underlying aggregation mechanism of this protein is dominated by secondary nucleation of monomers on fibril surface providing an autocatalytic amyloid amplification process. Bovine α-, βH- and γB-crystallins were found to display chaperone-like activity inhibiting α-synuclein aggregation. This effect was shown to be time-dependent, with early additions of α-crystallin capable of retarding and even inhibiting aggregation during the time frame of the experiment. The inhibitory nature of crystallins was further investigated using trap and seed kinetic experiments. We propose crystallins interact with mature α-synuclein fibrils, possibly binding along the surfaces and at fibril free ends, inhibiting both elongation and monomer-dependent secondary nucleation processes in a mechanism that may be generic to some chaperones that prevent the onset of protein misfolding related pathologies.
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| 13. |
- Gibaud, Thomas, et al.
(författare)
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New routes to food gels and glasses
- 2012
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498 .- 1359-6640. ; 158, s. 267-284
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Tidskriftsartikel (refereegranskat)abstract
- We describe the possibility to create solid-like protein samples whose structural and mechanical properties can be varied and tailored over an extremely large range in a very controlled way through an arrested spinodal decomposition process. We use aqueous lysozyme solutions as a model globular protein system. A combination of video microscopy, small-angle neutron and X-ray scattering and reverse Monte Carlo modeling is used to characterize the structure of the bicontinuous network with two coexisting phases of a dilute protein solution and a glassy or arrested dense protein backbone at all relevant length scales. Rheological measurements are then used to determine the complex mechanical response of these protein gels as a function of protein concentration and quench temperature. While in particular the origin of the dependence of the mechanical properties on quench depth and concentration is not well understood currently, it seems ultimately connected to the particular bicontinuous structure of the arrested spinodal network created by the interplay between the early stage of a spinodal decomposition and the position of the glass line. We then generalize this behavior and discuss how this could open up new routes to prepare gel-like food systems with adjustable structural and mechanical properties. We present results from a first feasibility study where we use a depletion interaction caused by the addition of small non-adsorbing polymers to suspensions of casein micelles in order to create food gels with tunable structural and mechanical properties through an arrested spinodal decomposition process.
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| 14. |
- Gibaud, Thomas, et al.
(författare)
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Phase separation and dynamical arrest for particles interacting with mixed potentials—the case of globular proteins revisited
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 7:2, s. 857-860
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Tidskriftsartikel (refereegranskat)abstract
- We examine the applicability of the extended law of corresponding states (ELCS) to equilibrium and non equilibrium features of the state diagram of the globular protein lysozyme. We provide compelling evidence that the ELCS correctly reproduces the location of the binodal for different ionic strengths, but fails in describing the location of the arrest line. We subsequently use Mode Coupling Theory (MCT) to gain additional insight into the origin of these observations. We demonstrate that while the critical point and the connected binodal and spinodal are governed by the integral features of the interaction potential described by the normalized second virial coefficient, the arrest line is mainly determined by the attractive well depth or bond strength.
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| 15. |
- Gulotta, Alessandro, et al.
(författare)
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Combining Scattering Experiments and Colloid Theory to Characterize Charge Effects in Concentrated Antibody Solutions
-
Ingår i: Molecular Pharmaceutics. - 1543-8384.
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Tidskriftsartikel (refereegranskat)abstract
- Charges and their contribution to protein-protein interactions are essential for the key structural and dynamic properties of monoclonal antibody (mAb) solutions. In fact, they influence the apparent molecular weight, the static structure factor, the collective diffusion coefficient, or the relative viscosity, and their concentration dependence. Further, charges play an important role in the colloidal stability of mAbs. There exist standard experimental tools to characterize mAb net charges, such as the measurement of the electrophoretic mobility, the second virial coefficient, or the diffusion interaction parameter. However, the resulting values are difficult to directly relate to the actual overall net charge of the antibody and to theoretical predictions based on its known molecular structure. Here, we report the results of a systematic investigation of the solution properties of a charged IgG1 mAb as a function of concentration and ionic strength using a combination of electrophoretic measurements, static and dynamic light scattering, small-angle X-ray scattering, and tracer particle-based microrheology. We analyze and interpret the experimental results using established colloid theory and coarse-grained computer simulations. We discuss the potential and limits of colloidal models for the description of the interaction effects of charged mAbs, in particular pointing out the importance of incorporating shape and charge anisotropy when attempting to predict structural and dynamic solution properties at high concentrations.
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| 16. |
- Mahmoudi, Najet, et al.
(författare)
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Making Food Protein Gels via an Arrested Spinodal Decomposition
- 2015
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:50, s. 15522-15529
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Tidskriftsartikel (refereegranskat)abstract
- We report an investigation of the structural and dynamic properties of mixtures of food colloid casein micelles and low molecular weight poly(ethylene oxide). A combination of visual observations, confocal laser scanning microscopy, diffusing wave spectroscopy, and oscillatory shear rheometry is used to characterize the state diagram of the mixtures and describe the structural and dynamic properties of the resulting fluid and solid-like structures. We demonstrate the formation of gel-like structures through an arrested spinodal decomposition mechanism. We discuss our observations in view of previous experimental and theoretical studies with synthetic and food colloids, and comment on the potential of such a route toward gels for food processing.
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| 17. |
- Mohanty, Priti S., et al.
(författare)
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Interpenetration of polymeric microgels at ultrahigh densities
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Soft particles such as polymeric microgels can form ultra-dense phases, where the average center-to-center distance a s can be smaller than the initial unperturbed particle diameter σ 0, due to their ability to interpenetrate and compress. However, despite of the effort devoted to microgels at ultrahigh densities, we know surprisingly little about their response to their environment at effective volume fractions φ eff above close packing (φ cp ), and the existing information is often contradictory. Here we report direct measurements of the size and shape of poly(N-isopropylacrylamide) microgels at concentrations below and above φcp using the zero average contrast method in small-angle neutron scattering. We complement these experiments with measurements of the average interparticle distances using small-angle X-ray scattering, and a determination of the glass transition using dynamic light scattering. This allows us to unambiguously decouple interaction effects from density-dependent variations of the particle size and shape at all values of φeff . We demonstrate that the microgels used in this study significantly interpenetrate and thus change their size and shape only marginally even for φeff > φ cp, a finding that may require changes in the interpretation of a number of previously published studies on the structural and dynamic properties of dense soft particle systems.
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| 18. |
- Moitzi, Christian, et al.
(författare)
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The pH Induced Sol-Gel Transition in Skim Milk Revisited. A Detailed Study Using Time-Resolved Light and X-ray Scattering Experiments
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:6, s. 2195-2203
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of the evolution of the size, structure and stability of casein micelles upon acidification of skim milk typically applied in yogurt-making processes using a combination of time-resolved light and small-angle X-ray scattering experiments. While most of the available light scattering studies on casein acidification have been restricted to transparent and therefore highly diluted samples, we now profit from a newly developed multiangle 3D light scattering instrument, which allows for time-resolved measurements in highly turbid samples. Our experiments clearly demonstrate the presence of two parallel pH-dependent processes, micellar reassembly and aggregation. Using a systematic investigation of the effect of casein concentration, acidification rate, and ionic strength, we are able to decouple these two processes and obtain detailed information about the pH-induced restructuration of the casein micelle structure that occurs prior to destabilization. Moreover, our experiments also unambiguously demonstrate that these micellar reassembly processes are highly concentration dependent, and that typical light scattering studies conducted under highly diluted conditions are resulting in findings that may not be relevant for the situation encountered in industrial processes at higher concentrations. Experiments conducted with covalently cross-linked micelles, where the pH-induced reassembly has been suppressed, further confirm our findings.
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| 19. |
- Myung, Jin Suk, et al.
(författare)
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Weak Shape Anisotropy Leads to a Nonmonotonic Contribution to Crowding, Impacting Protein Dynamics under Physiologically Relevant Conditions
- 2018
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a nonspherical particle shape on the dynamics in crowded solutions presents a significant challenge for a comprehensive understanding of interaction and structural relaxation in biological and soft matter. We report that small deviations from a spherical shape induce a nonmonotonic contribution to the crowding effect on the short-time cage diffusion compared with spherical systems, using molecular dynamics simulations with mesoscale hydrodynamics of a multiparticle collision dynamics fluid in semidilute systems with volume fractions smaller than 0.35. We show that the nonmonotonic effect due to anisotropy is caused by the combination of a reduced relative mobility over the entire concentration range and a looser and less homogeneous cage packing of nonspherical particles. Our finding stresses that nonsphericity induces new complexity, which cannot be accounted for in effective sphere models, and is of great interest in applications such as formulations as well as for the fundamental understanding of soft matter in general and crowding effects in living cells in particular.
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| 20. |
- Oskolkova, Malin Zackrisson, 1974, et al.
(författare)
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Concentration-dependent effective attractions between PEGylated nanoparticles
- 2015
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Ingår i: RSC Advances. - 2046-2069. ; 5:32, s. 25149-25155
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Tidskriftsartikel (refereegranskat)abstract
- Effective attractions between colloidal particles bearing a grafted poly(ethylene glycol) (PEG) layer in water have been studied and quantified by measurements of the collective diffusion coefficient and by quantitative analysis of small-angle neutron scatterin (SANS) data. Results for the collective diffusion coefficient in the dilute limit indicate that effective attractions develop gradually as carbonate anions are added to the dispersions. Analysis of SANS data within a square-well interaction model at a constant salt concentration allows for quantitative analysis of scattering patterns of samples prior to crossing into an aggregation regime, where particles form large clusters, reached either through increasing the temperature or the particle concentration. Aggregation is observed visually and is also evident in the scattering as a lowering of the intensity at intermediate wavevectors while leaving enhanced scattering in the forward direction, suggesting a nearby fluid–fluid phase transition. In addition, at low and moderate particle concentrations the attraction strength is shown to depend mainly on temperature but at high particle concentrations a much stronger temperature dependence is observed, which shows that the attraction acquires a dependence on particle concentration at sufficiently high concentrations. The concentration dependence is attributed to a decreased solvation of PEG chains due to an increased ratio of ethylene oxide segments to water.
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