Interplay between Spinodal Decomposition and Glass Formation in Proteins Exhibiting Short-Range Attractions

We investigate the competition between spinodal decomposition and dynamical arrest using aqueous solutions of the globular protein lysozyme as a model system for colloids with short-range attractions. We show that quenches below a temperature Ta lead to gel formation as a result of a local arrest of the proteindense phase during spinodal decomposition. The rheological properties of these gels allow us to use centrifugation experiments to determine the local densities of both phases and to precisely locate the gel boundary and the attractive glass line close to and within the unstable region of the phase diagram

Modeling Equilibrium Clusters in Lysozyme Solutions

We present a combined experimental and numerical study of the equilibrium cluster formation in globular protein solutions under no-added salt conditions. We show that a cluster phase emerges as a result of a competition between a long-range screened Coulomb repulsion and a short-range attraction. A simple effective potential, in which only depth and width of the attractive part of the potential are optimized, accounts in a remarkable way for the wavevector dependence of the X-ray scattering structure factor.Comment: 4 pages, 4 figure

Bio-, Magneto- and event-stratigraphy across the K-T boundary

Determining the time and the time structure of rare events in geology can be accomplished by applying three different and independent stratigraphic methods: Biostratigraphy, magneto-stratigraphy and event-stratigraphy. The optimal time resolution of the two former methods is about 1000 years, while by means of event-stratigraphy a resolution of approximately one year can be achieved. For biostratigraphy across the Cretaceous-Tertiary (K-T) boundary micro- and nannofossils have been found best suited. The qualitative and quantitative analyses of minerals and trace elements across the K-T boundary show anomalies on a millimeter scale and permit conclusions regarding the time structure of the K-T event itself. The results of the analyses find a most consistent explanation by the assumption of an extraterrestrial impact. The main portion of the material rain from the atmosphere evidently was deposited within a short time. The long-time components consist of the finest portion of the material rain from the atmosphere and the transported and redeposited fall-out

Interplay between spinodal decomposition and glass formation in proteins exhibiting short-range attractions

We investigate the competition between spinodal decomposition and dynamical arrest using aqueous solutions of the globular protein lysozyme as a model system for colloids with short-range attractions. We show that quenches below a temperature Ta lead to gel formation as a result of a local arrest of the protein-dense phase during spinodal decomposition. The rheological properties of these gels allow us to use centrifugation experiments to determine the local densities of both phases and to precisely locate the gel boundary and the attractive glass line close to and within the unstable region of the phase diagram

Density-dependent interactions and structure of charged colloidal dispersions in the weak screening regime

We determine the structure of charge-stabilized colloidal suspensions at low ionic strength over an extended range of particle volume fractions using a combination of light and small angle neutron scattering experiments. The variation of the structure factor with concentration is analyzed within a one-component model of a colloidal suspension. We show that the observed structural behavior corresponds to a non-monotonic density dependence of the colloid effective charge and the mean interparticle interaction energy. Our findings are corroborated by similar observations from primitive model computer simulations of salt-free colloidal suspensions.Comment: Revised version, accepted to Phys. Rev. Let

A colloid approach to self-assembling antibodies

Concentrated solutions of monoclonal antibodies have attracted considerable attention due to their importance in pharmaceutical formulations, yet their tendency to aggregate and the resulting high solution viscosity has posed considerable problems. It remains a very difficult task to understand and predict the phase behavior and stability of such solutions. Here we present a systematic study of the concentration dependence of the structural and dynamic properties of monoclonal antibodies using a combination of different scattering methods and microrheological experiments. To interpret these data, we use a colloid-inspired approach based on a simple patchy model, which explicitly takes into account the anisotropic shape and the charge distribution of the molecules. Combining theory, simulations and experiments, we are able to disentangle self-assembly and intermolecular interactions and to quantitatively describe the concentration dependence of structural and dynamic quantities such as the osmotic compressibility, the collective diffusion coefficient and the zero shear viscosity over the entire range of investigated concentrations. This simple patchy model not only allows us to consistently describe the thermodynamic and dynamic behavior of mAb solutions, but also provides a robust estimate of the attraction between their binding sites. It will thus be an ideal starting point for future work on antibody formulations, as it provides a quantitative assessment of the effects of additional excipients or chemical modifications on antibody interactions, and a prediction of their effect on solution viscosity

New insight into cataract formation -- enhanced stability through mutual attraction

Small-angle neutron scattering experiments and molecular dynamics simulations combined with an application of concepts from soft matter physics to complex protein mixtures provide new insight into the stability of eye lens protein mixtures. Exploring this colloid-protein analogy we demonstrate that weak attractions between unlike proteins help to maintain lens transparency in an extremely sensitive and non-monotonic manner. These results not only represent an important step towards a better understanding of protein condensation diseases such as cataract formation, but provide general guidelines for tuning the stability of colloid mixtures, a topic relevant for soft matter physics and industrial applications.Comment: 4 pages, 4 figures. Accepted for publication on Phys. Rev. Let

A new instrument for time-resolved static and dynamic light-scattering experiments in turbid media

We present a new 3D cross-correlation instrument that not only allows for static and dynamic scattering experiments with turbid samples but measures at four angles simultaneously. It thus extends the application of cross-correlation light scattering to time-resolved studies where we can, for example, efficiently investigate the temporal evolution of aggregating or phase separating turbid dispersions. The combination of multiangle 3D and on-line transmission measurements is an essential prerequisite for such studies. This not only provides time-resolved information about the overall size and shape of the particles through measurements of the mean apparent radius of gyration and hydrodynamic radius, but also on the weight-average apparent molar mass via the absolute forward scattering intensity. We present an efficient alignment strategy based on the novel design of the instrument and then the application range of the instrument using well-defined model latex suspensions. The effectiveness of the cross-correlation multiangle technique to monitor aggregation processes in turbid suspensions is finally shown for the acidification of skim milk during the yoghurt-making process. Due to the self-assembled nature of the casein micelles an understanding of the sol–gel process induced by the acidification is only feasible if time-resolved light-scattering experiments on an absolute scale are possible under industrially relevant conditions, where the casein solutions are highly turbid

Arrest transitions in protein solutions – insight from combining scattering, microrheology, and computer simulations

The static and dynamic properties of concentrated protein solutions are essential ingredients for our understanding of the cellular machinery or formulating biopharmaceuticals. Here a combination of advanced characterization techniques such as light and x-ray scattering, neutron spin echo measurements [1] and microrheology experiments [2], combined with the theoretical toolbox from colloid physics and state-of-the-art computer simulations [3], considerably enhances our understanding of the link between protein interactions and the stability, dynamics and flow properties of these solutions up to high concentrations. We will address the enormous influence of weak attractive interactions known to exist between many globular proteins, and demonstrate the dramatic effect of an interaction potential anisotropy [1] such as attractive patches and shape anisotropy [3] on the dynamic properties. We will also discuss how we can combine interparticle interaction effects and the formation of (transient) equilibrium clusters in an attempt to understand and predict properties such as the concentration dependence of the zero shear viscosity of dense protein solutions [4]. (1) Bucciarelli, S.; Myung, J. S.; Farago, B.; Das, S., Vliegenthart, G.; Holderer, O.; Winkler, R. G.; Schurtenberger, P.; Gompper, G.; Stradner, A. “Dramatic influence of patchy attractions on short-time protein diffusion under crowded conditions” Sci. Adv. 2016, 2:e1601432. (2) Garting, T. and Stradner, A. “Optical Microrheology of Protein Solutions using Tailored Nanoparticles” Small 2018, 1801548. (3) Myung, J. S.; Roosen-Runge, F.; Winkler, R. G.; Gompper, G.; Schurtenberger, P.; Stradner, A. “Weak shape anisotropy leads to non-monotonic crowding effects impacting protein dynamics under physiologically relevant conditions” J. Phys. Chem. B 2018, 122, 12396-12402. (4) Bergman, M.; Garting, T.; Schurtenberger, P.; Stradner, A. “Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions” submitted to J. Phys. Chem. B, 2019