Separation of Whey Protein Aggregates by Means of Continuous Centrifugation

Structural determinants of odorant-binding proteins affecting their ability to form amyloid fibrils

The formation of amyloid fibrils is associated with many severe pathologies as well as the execution of essential physiological functions by proteins. Despite the diversity, all amyloids share a similar morphology and consist of stacked β-strands, suggesting high amyloidogenicity of native proteins enriched with β-structure. Such proteins include those with a β-barrel-like structure with β-strands arranged into a cylindrical β-sheet. However, the mechanisms responsible for destabilization of the native state and triggering fibrillogenesis have not thoroughly explored yet. Here we analyze the structural determinants of fibrillogenesis in proteins with β-barrel structures on the example of odorant-binding protein (OBP), whose amyloidogenicity was recently demonstrated in vitro. We reveal a crucial role in the fibrillogenesis of OBPs for the "open" conformation of the molecule. This conformation is achieved by disrupting the interaction between the β-barrel and the C-terminus of protein monomers or dimers, which exposes "sticky" amyloidogenic sites for interaction. The data suggest that the "open" conformation of OBPs can be induced by destabilizing the native β-barrel structure through the disruption of: 1) intramolecular disulfide cross-linking and non-covalent contacts between the C-terminal fragment and β-barrel in the protein's monomeric form, or 2) intermolecular contacts involved in domain swapping in the protein's dimeric form.

Size distribution of migrating particles and droplets under gravity in concentrated dispersions measured with static multiple light scattering

HYPOTHESIS

Light scattering techniques can provide a non-intrusive measurement of particle and droplet size distribution but are limited to relatively diluted liquid dispersions. Measurement of particle velocity distributions (PVD) and particle/droplet size distributions (PSD) in diluted to highly concentrated solid suspensions and emulsions can be performed by coupling the static multiple light scattering technique (SMLS) to mathematical models describing the vertical motion under gravity of polydisperse particles and droplets.

EXPERIMENTS

Measurement of the PSD using SMLS was performed on silica particles dispersed in water with monomodal, bimodal and trimodal PSDs ranging from 570 nm and 7.90 µm. Quasi-monodisperse certified latex particles with 815 nm mean diameter dispersed in water and non-controlled emulsions of hexadecane-water emulsions at volume fractions ranging from 0.005 % to 20 % were also characterized with SMLS. These measurements were compared to certified size distributions, and to laser diffraction and dynamic light scattering measurements.

FINDINGS

Robust, highly resolutive and concentration-dependent measurement of the PVD and PSD of solid particles and droplets was achieved for diluted to highly concentrated liquid dispersions. As interactions between particles or droplets are dependent on the dispersed phase concentration, accurate characterization of as-formulated industrial liquid dispersions can be performed with SMLS.

Determination of Compressibility and Relaxation Behavior of Yeast Cell Sediments by Analytical Centrifugation and Comparison with Deposit Formation on Membrane Surfaces

Separation of cells from produced biomolecules is a challenging task in many biotechnological downstream operations due to deposit formation of the retained cells, affecting permeation of the target product. Compression and relaxation behavior of cell deposits formed during filtration are important factors affecting operational performance. The determination of these factors by flux or pressure stepping experiments is time- and labor-intensive. In this work, we propose a screening method by analytical centrifugation, which is capable of detecting small differences in compression and relaxation behavior induced by milieu changes, using a model system comprised of washed and unwashed yeast cells in the presence or absence of bovine serum albumin as a model target protein. The main effects observed were firstly the impact of pH value, affecting interaction of bovine serum albumin and yeast cells especially close to the isoelectric point, and secondly the effect of washing the yeast cells prior to analysis, where the presence of extracellular polymeric substances led to higher compressibility of the deposited cells. By comparing and validating the obtained results with dead-end filtration trials, the stabilizing role of bovine serum albumin in deposits formed at low pH values due to interactions with the yeast cells was underlined.

Enhanced filtration performance using feed-and-bleed configuration for purification of antibody precipitates

Precipitation can be used for the initial purification of monoclonal antibodies (mAbs), with the soluble host cell proteins removed in the permeate by tangential flow microfiltration. The objective of this study was to examine the use of a feed-and-bleed configuration to increase the effective conversion (ratio of permeate to feed flow rates) in the hollow fiber module to enable more effective washing of the precipitate. Experiments were performed using human serum Immunoglobulin G (IgG) precipitates formed with 10 mM zinc chloride and 7 wt% polyethylene glycol. The critical flux was evaluated as a function of the shear rate and IgG concentration, with the resulting correlation used to predict conditions that can achieve 90% conversion in a single pass with minimal fouling. Experimental data for both the start-up and steady-state performance are in good agreement with model calculations. These results were used to analyze the performance of an enhanced continuous precipitation-microfiltration process using the feed-and-bleed configuration for the initial capture / purification of a mAb product.

Influence of Thermomechanical Treatment and Ratio of β-Lactoglobulin and α-Lactalbumin on the Denaturation and Aggregation of Highly Concentrated Whey Protein Systems

The influence of thermomechanical treatment (temperature 60 °C-100 °C and shear rate 0.06 s-1-50 s-1) and mixing ratio of β-lactoglobulin (βLG) and α-lactalbumin (αLA) (5:2 and 1:1) on the denaturation and aggregation of whey protein model systems with a protein concentration of 60% and 70% (w/w) was investigated. An aggregation onset temperature was determined at approx. 80 °C for both systems (5:2 and 1:1 mixing ratio) with a protein concentration of 70% at a shear rate of 0.06 s-1. Increasing the shear rate up to 50 s-1 led to a decrease in the aggregation onset temperature independent of the mixing ratio. By decreasing the protein concentration to 60% in unsheared systems, the aggregation onset temperature decreased compared to that at a protein concentration of 70%. Furthermore, two significantly different onset temperatures were determined when the shear rate was increased to 25 s-1 and 50 s-1, which might result from a shear-induced phase separation. Application of combined thermal and mechanical treatment resulted in overall higher degrees of denaturation independent of the mixing ratio and protein concentration. At the conditions applied, the aggregation of the βLG and αLA mixtures was mainly due to the formation of non-covalent bonds. Although the proportion of disulfide bond aggregation increased with treatment temperature and shear rate, it was higher at a mixing ratio of 5:2 compared to that at 1:1.