The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
D Durand - One of the best experts on this subject based on the ideXlab platform.
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particle diffusion in Globular Protein gels in relation to the gel structure
Biomacromolecules, 2011Co-Authors: Gireeshkumar Balakrishnan, D Durand, Taco NicolaiAbstract:Globular Protein gels with a variety of structures were prepared by heating β-lactoglobulin solutions at different concentrations and different ionic strengths. The structure was analyzed in terms of the pair correlation function of the Protein concentration, and the volume fraction of the gels was determined. A strong coarsening of the gel structure was observed upon increasing the NaCl concentration between 0.1 and 0.25 M. The mean square displacement of spherical particles with diameters between 0.2 and 2 μm was determined in solutions and in gels by multiparticle tracking of confocal laser scanning microscopy images. Brownian diffusion or trapping of spheres with different sizes was observed, depending on the gel structure. In few cases the diffusion was anomalous. The relationship between gel structure and particle mobility is discussed.
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salt induced gelation of Globular Protein aggregates structure and kinetics
Biomacromolecules, 2010Co-Authors: Taco Nicolai, D DurandAbstract:Aggregates of the Globular Protein β-lactoglobulin were formed by heating solutions of native Proteins at pH 7, after which gels were formed by the addition of salt. The second step does not necessitate elevated temperatures and is therefore often called cold gelation. The structure of the gels was studied during their formation using light scattering and turbidity. Complementary confocal laser scanning microscopy measurements were done. We compared the structure with that of gels formed by heating native β-lactoglobulin under the same conditions. Whereas in the latter case, microphase separation occurs above 0.2 M NaCl, no microphase separation was observed during cold gelation up to at least 1 M NaCl. The dependence of the kinetics and the final gel structure on the Protein concentration, the temperature, the salt concentration, and the aggregate size was quantified. A few measurements on gels formed by adding CaCl2 confirmed the higher efficiency of this bivalent cation but revealed no qualitative diff...
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quantitative analysis of confocal laser scanning microscopy images of heat set Globular Protein gels
Food Hydrocolloids, 2009Co-Authors: D Durand, Taco Nicolai, Lydiane BecuAbstract:Gels of the Globular Protein β-lactoglobulin were made by heating solutions at pH 7 and different NaCI concentrations (C s ). The influence of the ionic strength on the gel structure was studied by confocal laser scanning microscopy (CLSM). For C s < 0.2 M the images were homogeneous, but at higher NaCI concentrations micro-phase separation was observed. The Protein concentration in the two phases was determined from the images. It is shown how CLSM images can be quantitatively analysed in terms of the pair correlation function of the Protein concentration fluctuations, yielding results that can be directly compared to those obtained from light scattering. The transition between so-called finely stranded and particulate gels is explained by a switch from net repulsive to net attractive interaction between growing Protein aggregates.
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light scattering study of heat denatured Globular Protein aggregates
International Journal of Biological Macromolecules, 2008Co-Authors: Soraya Mehalebi, Taco Nicolai, D DurandAbstract:Abstract The structure of aggregates formed by the Globular Protein β-lactoglobulin (β-lg) after heat induced denaturation was studied using light scattering and size exclusion chromatography. The influence of varying the pH above the iso-electric point (pH 5.2) was investigated in the absence of added salt. Stable aggregates could be formed and characterized between pH 5.8 and pH 9. The large-scale structure of the aggregates was self-similar and remarkably insensitive to the pH. Below a critical association concentration, which decreased with decreasing pH from 10 to 1 g/L, denatured monomers and small oligomers were formed. At higher concentrations larger so-called preaggregates formed containing roughly 100 monomers. With increasing concentration the size of the aggregates varied little until it rose sharply close to the gelation concentration that decreased with decreasing pH (50 g/L
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the influence of electrostatic interaction on the structure and the shear modulus of heat set Globular Protein gels
Soft Matter, 2008Co-Authors: Soraya Mehalebi, Taco Nicolai, D DurandAbstract:Gels formed by the Globular Protein β-lactoglobulin after heat denaturation were studied using light scattering, turbidity and shear oscillation measurements. The structure of the gels was characterized in terms of the amplitude and the correlation length of concentration fluctuations. The strength of electrostatic interactions was varied by changing the pH in the absence of added salt or by changing the NaCl concentration at pH 7. A very strong increase of the heterogeneity of the gels was observed when decreasing the pH towards the isoelectric point or when increasing the salt concentration. The structural change was interpreted in terms of a decrease of the net repulsion between the growing aggregates leading to increased concentration fluctuations and finally microscopic phase separation. The elastic shear modulus increased with decreasing pH and showed a maximum as a function of the NaCl concentration. No direct correlation between the change in the structure and the elastic modulus was found.
Taco Nicolai - One of the best experts on this subject based on the ideXlab platform.
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polymer probe diffusion in Globular Protein gels and aggregate suspensions
Journal of Physical Chemistry B, 2018Co-Authors: Walailuk Inthavong, Taco Nicolai, Christophe ChassenieuxAbstract:Transport properties of macromolecules in dense aggregate suspensions and gels of Proteins are important for usage of these biomaterials in areas such as pharmaceutics, food, and cosmetics. The mobility of polymers in Protein gels has received some attention in the past, but the mobility in dense aggregate suspensions has not yet been investigated. In this study, self-diffusion of probe dextran chains was studied in suspensions of aggregates with different size and morphology and in gels using fluorescence recovery after photobleaching over a wide range of concentrations. Brownian diffusion of the probes was observed in aggregate suspensions as well as in weak gels formed just beyond the critical gel concentration. Diffusion of polymers in dense suspensions of Protein aggregates depends not only on the concentration but also on the size and morphology of the aggregates. It is not directly related to the viscosity or the dynamic correlation length. Diffusion of polymers in Protein gels is anomalous and occ...
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particle diffusion in Globular Protein gels in relation to the gel structure
Biomacromolecules, 2011Co-Authors: Gireeshkumar Balakrishnan, D Durand, Taco NicolaiAbstract:Globular Protein gels with a variety of structures were prepared by heating β-lactoglobulin solutions at different concentrations and different ionic strengths. The structure was analyzed in terms of the pair correlation function of the Protein concentration, and the volume fraction of the gels was determined. A strong coarsening of the gel structure was observed upon increasing the NaCl concentration between 0.1 and 0.25 M. The mean square displacement of spherical particles with diameters between 0.2 and 2 μm was determined in solutions and in gels by multiparticle tracking of confocal laser scanning microscopy images. Brownian diffusion or trapping of spheres with different sizes was observed, depending on the gel structure. In few cases the diffusion was anomalous. The relationship between gel structure and particle mobility is discussed.
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salt induced gelation of Globular Protein aggregates structure and kinetics
Biomacromolecules, 2010Co-Authors: Taco Nicolai, D DurandAbstract:Aggregates of the Globular Protein β-lactoglobulin were formed by heating solutions of native Proteins at pH 7, after which gels were formed by the addition of salt. The second step does not necessitate elevated temperatures and is therefore often called cold gelation. The structure of the gels was studied during their formation using light scattering and turbidity. Complementary confocal laser scanning microscopy measurements were done. We compared the structure with that of gels formed by heating native β-lactoglobulin under the same conditions. Whereas in the latter case, microphase separation occurs above 0.2 M NaCl, no microphase separation was observed during cold gelation up to at least 1 M NaCl. The dependence of the kinetics and the final gel structure on the Protein concentration, the temperature, the salt concentration, and the aggregate size was quantified. A few measurements on gels formed by adding CaCl2 confirmed the higher efficiency of this bivalent cation but revealed no qualitative diff...
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quantitative analysis of confocal laser scanning microscopy images of heat set Globular Protein gels
Food Hydrocolloids, 2009Co-Authors: D Durand, Taco Nicolai, Lydiane BecuAbstract:Gels of the Globular Protein β-lactoglobulin were made by heating solutions at pH 7 and different NaCI concentrations (C s ). The influence of the ionic strength on the gel structure was studied by confocal laser scanning microscopy (CLSM). For C s < 0.2 M the images were homogeneous, but at higher NaCI concentrations micro-phase separation was observed. The Protein concentration in the two phases was determined from the images. It is shown how CLSM images can be quantitatively analysed in terms of the pair correlation function of the Protein concentration fluctuations, yielding results that can be directly compared to those obtained from light scattering. The transition between so-called finely stranded and particulate gels is explained by a switch from net repulsive to net attractive interaction between growing Protein aggregates.
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light scattering study of heat denatured Globular Protein aggregates
International Journal of Biological Macromolecules, 2008Co-Authors: Soraya Mehalebi, Taco Nicolai, D DurandAbstract:Abstract The structure of aggregates formed by the Globular Protein β-lactoglobulin (β-lg) after heat induced denaturation was studied using light scattering and size exclusion chromatography. The influence of varying the pH above the iso-electric point (pH 5.2) was investigated in the absence of added salt. Stable aggregates could be formed and characterized between pH 5.8 and pH 9. The large-scale structure of the aggregates was self-similar and remarkably insensitive to the pH. Below a critical association concentration, which decreased with decreasing pH from 10 to 1 g/L, denatured monomers and small oligomers were formed. At higher concentrations larger so-called preaggregates formed containing roughly 100 monomers. With increasing concentration the size of the aggregates varied little until it rose sharply close to the gelation concentration that decreased with decreasing pH (50 g/L
Bradley D. Olsen - One of the best experts on this subject based on the ideXlab platform.
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Effect of polymer chemistry on Globular Protein–polymer block copolymer self-assembly
Polymer Chemistry, 2020Co-Authors: Dongsook Chang, Shengchang Tang, Bradley D. OlsenAbstract:Bioconjugates of the model red fluorescent Protein mCherry and synthetic polymer blocks with different hydrogen bonding functionalities show that the chemistry of the polymer block has a large effect on both ordering transitions and the type of nanostructures formed during bioconjugate self-assembly. The phase behaviours of mCherry-b-poly(hydroxypropyl acrylate) (PHPA) and mCherry-b-poly(oligoethylene glycol acrylate) (POEGA) in concentrated aqueous solution show that changes in polymer chemistry result in increase in the order–disorder transition concentrations (CODTs) by approximately 10–15 wt% compared to a previously studied Globular Protein–polymer block copolymer, mCherry-b-poly(N-isopropylacrylamide) (PNIPAM). The CODTs are always minimized for symmetric bioconjugates, consistent with the importance of Protein–polymer interactions in self-assembly. Both mCherry-b-PHPA and mCherry-b-POEGA also form phases that have not previously been observed in other Globular Protein–polymer conjugates: mCherry-b-PHPA forms a cubic phase that can be indexed to Iad and mCherry-b-POEGA displays coexistence of lamellae and a cubic Iad structure over a narrow range of concentration and temperature. Several common behaviours are also revealed by comparison of different polymer blocks. With increasing concentration and temperature, ordered phases always appear in the order lamellar, cubic/PL, and hexagonal, although not all phases are observed in all materials. High concentration solutions (near 80 wt%) also undergo a re-entrant order–disorder transition to form nematic liquid crystalline phases, regardless of the polymer block chemistry.
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secondary structure drives self assembly in weakly segregated Globular Protein rod block copolymers
Polymer Chemistry, 2020Co-Authors: Kai Sheng, Hua Lu, Bradley D. OlsenAbstract:Protein–polymer bioconjugates represent a class of materials that integrate Protein functionality with polymer material properties and block copolymer self-assembly. To investigate the effect of polymer block secondary structure and chirality on self-assembly of Globular Protein–helix diblock copolymers, four types of bioconjugates consisting of a poly(amino acid) and enhanced green fluorescent Protein (eGFP) were synthesized and compared: two homochiral, α-helix-forming bioconjugates incorporating either L- or D-type poly(amino acids), a 1 : 1 blend of the L- and D-type bioconjugates, and a bioconjugate incorporating structureless, achiral poly(amino acids). Poly(amino acids) (PAAs) were synthesized via N-carboxy anhydride (NCA) polymerization, and PAAs were conjugated to eGFP via native chemical ligation. All bioconjugates with a helical block self-assembled into lamellae at all concentrations measured (20 to 60 wt%). In contrast, the random copolymer of L- and D-type monomers did not self-assemble at any concentration or temperature. This was shown to be an effect of a non-repulsive interaction between the flexible PAA and the eGFP blocks, which is strong enough to affect the protonation state of the eGFP chromophore in water. Therefore, secondary structure of the polymer block can modulate the effective segregation strength between blocks and drive self-assembly even in systems with non-repulsive blocks.
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topological effects on Globular Protein elp fusion block copolymer self assembly
Advanced Functional Materials, 2015Co-Authors: Matthew J Glassman, Dongsook Chang, Eric Schaible, Alexander Hexemer, Bradley D. OlsenAbstract:Perfectly defined, monodisperse fusion Protein block copolymers of a thermoresponsive coil-like Protein, ELP, and a Globular Protein, mCherry, are demonstrated to act as fully biosynthetic analogues to Protein-polymer conjugates that can self-assemble into biofunctional nanostructures such as hexagonal and lamellar phases in concentrated solutions. The phase behavior of two mCherry-ELP fusions, E10-mCherry-E10 and E20-mCherry, is investigated to compare linear and bola fusion self-assembly both in diluted and concentrated aqueous solution. In dilute solution, the molecular topology impacts the stability of micelles formed above the thermal transition temperature of the ELP block, with the diblock forming micelles and the bola forming unstable aggregates. Despite the chemical similarity of the two Protein blocks, the materials order into block copolymer-like nanostructures across a wide range of concentrations at 30 wt% and above, with the bola fusion having a lower order-disorder transition concentration than the diblock fusion. The topology of the molecule has a large impact on the type of nanostructure formed, with the two fusions forming phases in the opposite order as a function of temperature and concentration. This new system provides a rich landscape to explore the capabilities of fusion architecture to control supramolecular assemblies for bioactive materials.
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effect of polymer chemistry on Globular Protein polymer block copolymer self assembly
Polymer Chemistry, 2014Co-Authors: Dongsook Chang, Shengchang Tang, Bradley D. OlsenAbstract:Bioconjugates of the model red fluorescent Protein mCherry and synthetic polymer blocks with different hydrogen bonding functionalities show that the chemistry of the polymer block has a large effect on both ordering transitions and the type of nanostructures formed during bioconjugate self-assembly. The phase behaviours of mCherry-b-poly(hydroxypropyl acrylate) (PHPA) and mCherry-b-poly(oligoethylene glycol acrylate) (POEGA) in concentrated aqueous solution show that changes in polymer chemistry result in increase in the order–disorder transition concentrations (CODTs) by approximately 10–15 wt% compared to a previously studied Globular Protein–polymer block copolymer, mCherry-b-poly(N-isopropylacrylamide) (PNIPAM). The CODTs are always minimized for symmetric bioconjugates, consistent with the importance of Protein–polymer interactions in self-assembly. Both mCherry-b-PHPA and mCherry-b-POEGA also form phases that have not previously been observed in other Globular Protein–polymer conjugates: mCherry-b-PHPA forms a cubic phase that can be indexed to Iad and mCherry-b-POEGA displays coexistence of lamellae and a cubic Iad structure over a narrow range of concentration and temperature. Several common behaviours are also revealed by comparison of different polymer blocks. With increasing concentration and temperature, ordered phases always appear in the order lamellar, cubic/PL, and hexagonal, although not all phases are observed in all materials. High concentration solutions (near 80 wt%) also undergo a re-entrant order–disorder transition to form nematic liquid crystalline phases, regardless of the polymer block chemistry.
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coil fraction dependent phase behaviour of a model Globular Protein polymer diblock copolymer
Soft Matter, 2014Co-Authors: Carla S Thomas, Bradley D. OlsenAbstract:The self-assembly of the model Globular Protein–polymer block copolymer mCherry-b-poly(N-isopropyl acrylamide) is explored across a range of polymer coil fractions from 0.21 to 0.82 to produce a phase diagram for these materials as a function of molecular composition. Overall, four types of morphologies were observed: hexagonally packed cylinders, perforated lamellae, lamellae, and disordered nanostructures. Across all coil fractions and morphologies, a lyotropic re-entrant order–disorder transition in water was observed, with disordered structures below 30 wt% and above 70 wt% and well-ordered morphologies at intermediate concentrations. Solid state samples prepared by solvent evaporation show moderately ordered structures similar to those observed in 60 wt% solutions, suggesting that bulk structures result from kinetic trapping of morphologies which appear at lower concentrations. While highly ordered cylindrical nanostructures are observed around a bioconjugate polymer volume fraction of 0.3 and well-ordered lamellae are seen near a volume fraction of 0.6, materials at lower or higher coil fractions become increasingly disordered. Notable differences between the phase behaviour of Globular Protein–polymer block copolymers and coil–coil diblock copolymers include the lack of spherical nanostructures at either high or low polymer coil fractions as well as shifted phase boundaries between morphologies which result in an asymmetric phase diagram.
Simon B Rossmurphy - One of the best experts on this subject based on the ideXlab platform.
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novel amyloid fibrillar networks derived from a Globular Protein β lactoglobulin
Langmuir, 2002Co-Authors: Walraj S Gosal, Allan H Clark, Paul D A Pudney, Simon B RossmurphyAbstract:Biology provides us with a unique set of self-assembled fibrillar networks in the form of amyloid fibrils, derived from the self-assembly of a number of peptides or misfolded Proteins. These, in turn, are associated with a number of diseases such as Alzheimer's, Creutzfeldt−Jakob disease (CJD), and type II diabetes. Recently, generating such supramolecular peptidic structures in vitro has led to a class of novel materials. In this multidistance scale, multidisciplinary study, we highlight various regimes whereby fibrils may be engineered by initiating self-assembly through the unfolding of a non-disease- associated Globular Protein, β-lactoglobulin (Mw ∼ 18 000, 162 residues). In particular, fibrils were generated by traditional thermal methods at pH 2, or, in a novel approach, by incubation in solvent−water mixtures such as water−2,2,2-trifluoroethanol. These treatments lead to fibrils of distinct structure and morphology. Secondary structure analyses of these by Fourier transform infrared spectroscopy (...
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Globular Protein gelation theory and experiment
Food Hydrocolloids, 2001Co-Authors: A H Clark, Gaynor M Kavanagh, Simon B RossmurphyAbstract:Heat-set Globular Protein gel networks are discussed in relation to Protein charge and screening. Homogeneous fine-stranded' gels form when electrostatic repulsion is high, with a transition to microphase-separated structures as repulsion falls. Fine-stranded networks showing density fluctuations occur close to this transition and probably arise from a combination of kinetic trapping and a drive towards only limited phase separation. For the most uniform structures (pH far from pI, and low salt content) network building appears to involve three main stages: initial Protein unfolding, linear fibrillar aggregation, and random cross-linking of the fibrils. A mean field model is described which incorporates these features and includes the possibility of cooperative linear aggregation (nucleation and growth). Application of this to cure data for acid β-lactoglobulin gels was only partially successful, however, a higher order (n = 4) nucleation process being required to explain gel time-concentration data, while only a lower second order process could reproduce the shapes of the cure curves. As uniform gels give way to phase-separated structures network building becomes still more complex. Here solution demixing of unfolded monomers, and/or the initial aggregates, must be included in the model. This seems beyond the current mean-field approach, and simulation is likely to be required. This is true, even for the more homogeneous structures, when gel properties of interest extend from the linear elastic, to the time-dependent, and non-linear. La gelification induite par la chaleur des Proteines globulaires est etudiee par rapport aux charges des Proteines et a l'effet d'ecran. Des gels homogenes se forment quand la repulsion electrostatique est forte, avec une transition vers des structures separees en microphases quand la repulsion diminue.
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Globular Protein gelation
Current Opinion in Colloid and Interface Science, 2000Co-Authors: Walraj S Gosal, Simon B RossmurphyAbstract:In this paper, significant advances in the structure and rheological properties of Globular Protein gels have been described. The achievements of scattering methods, which have provided information over a range of distances from the monomer to the micron scale, are reviewed. The kinetics of gelation measured by rheological methods have also been discussed, including currently applied models for the gelation time, the gel elastic modulus and the critical gel concentration.
Christopher M Dobson - One of the best experts on this subject based on the ideXlab platform.
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mutational analysis of the propensity for amyloid formation by a Globular Protein
The EMBO Journal, 2000Co-Authors: Fabrizio Chiti, Niccolo Taddei, Monica Bucciantini, Paul White, Giampietro Ramponi, Christopher M DobsonAbstract:Acylphosphatase can be converted in vitro, by addition of trifluoroethanol (TFE), into amyloid fibrils of the type observed in a range of human diseases. The propensity to form fibrils has been investigated for a series of mutants of acylphosphatase by monitoring the range of TFE concentrations that result in aggregation. We have found that the tendency to aggregate correlates inversely with the conformational stability of the native state of the Protein in the different mutants. In accord with this, the most strongly destabilized acylphosphatase variant forms amyloid fibrils in aqueous solution in the absence of TFE. These results show that the aggregation process that leads to amyloid deposition takes place from an ensemble of denatured conformations under conditions in which non-covalent interactions are still favoured. These results support the hypothesis that the stability of the native state of Globular Proteins is a major factor preventing the in vivo conversion of natural Proteins into amyloid fibrils under non-pathological conditions. They also suggest that stabilizing the native states of amyloidogenic Proteins could aid prevention of amyloidotic diseases.
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slow cooperative folding of a small Globular Protein hpr
Biochemistry, 1998Co-Authors: N A J Van Nuland, Wim Meijberg, Jane Warner, Vincent Forge, Ruud M Scheek, George T Robillard, Christopher M DobsonAbstract:The folding of an 85-residue Protein, the histidine-containing phosphocarrier Protein HPr, has been studied using a variety of techniques including DSC, CD, ANS fluorescence, and NMR spectroscopy. In both kinetic and equilibrium experiments the unfolding of HPr can be adequately described as a two-state process which does not involve the accumulation of intermediates. Thermodynamic characterization of the native and the transition states has been achieved from both equilibrium and kinetic experiments. The heat capacity change from the denatured state to the transition state (3.2 kJ mol-1 K-1) is half of the heat capacity difference between the native and denatured states (6.3 kJ mol-1 K-1), while the solvent accessibility of the transition state (0.36) indicates that its compactness is closer to that of the native than that of the denatured state. The high value for the change in heat capacity upon unfolding results in the observation of cold denaturation at moderate denaturant concentrations. Refolding f...