Concentrated Protein Solutions Research Articles

Testing mixing rules for structural and dynamical quantities in multi-component crowded protein solutions.

Crowding effects significantly influence the phase behavior and the structural and dynamic properties of the concentrated protein mixtures present in the cytoplasm of cells or in the blood serum. This poses enormous difficulties for our theoretical understanding and our ability to predict the behavior of these systems. While the use of course grained colloid-inspired models allows us to reproduce the key physical solution properties of concentrated monodisperse solutions of individual proteins, we lack corresponding theories for complex polydisperse mixtures. Here, we test the applicability of simple mixing rules in order to predict solution properties of protein mixtures. We use binary mixtures of the well-characterized bovine eye lens proteins α and γB crystallin as model systems. Combining microrheology with static and dynamic scattering techniques and observations of the phase diagram for liquid-liquid phase separation, we show that reasonably accurate descriptions are possible for macroscopic and mesoscopic signatures, while information on the length scale of the individual protein size requires more information on cross-component interaction.

Protein Adsorption on Solid Surfaces: Data Mining, Database, Molecular Surface-Derived Properties, and Semiempirical Relationships.

Protein adsorption on solid surfaces is a process relevant to biological, medical, industrial, and environmental applications. Despite this wide interest and advancement in measurement techniques, the complexity of protein adsorption has frustrated its accurate prediction. To address this challenge, here, data regarding protein adsorption reported in the last four decades was collected, checked for completeness and correctness, organized, and archived in an upgraded, freely accessible Biomolecular Adsorption Database, which is equivalent to a large-scale, ad hoc, crowd-sourced multifactorial experiment. The shape and physicochemical properties of the proteins present in the database were quantified on their molecular surfaces using an in-house program (ProMS) operating as an add-on to the PyMol software. Machine learning-based analysis indicated that protein adsorption on hydrophobic and hydrophilic surfaces is modulated by different sets of operational, structural, and molecular surface-based physicochemical parameters. Separately, the adsorption data regarding four "benchmark" proteins, i.e., lysozyme, albumin, IgG, and fibrinogen, was processed by piecewise linear regression with the protein monolayer acting as breakpoint, using the linearization of the Langmuir isotherm formalism, resulting in semiempirical relationships predicting protein adsorption. These relationships, derived separately for hydrophilic and hydrophobic surfaces, described well the protein concentration on the surface as a function of the protein concentration in solution, adsorbing surface contact angle, ionic strength, pH, and temperature of the carrying fluid, and the difference between pH and the isoelectric point of the protein. When applying the semiempirical relationships derived for benchmark proteins to two other "test" proteins with known PDB structure, i.e., β-lactoglobulin and α-lactalbumin, the errors of this extrapolation were found to be in a linear relationship with the dissimilarity between the benchmark and the test proteins. The work presented here can be used for the estimation of operational parameters modulating protein adsorption for various applications such as diagnostic devices, pharmaceuticals, biomaterials, or the food industry.

Competitive sorption of low and high molecular weight proteins in model mixtures by Q HyperZ chromatographic medium. Part II: Mass transfer mechanisms

The kinetic uptake of Bovine Serum Albumin (BSA) and ferritin in mixtures by the composite anion exchanger Q HyperZ was studied. Transient adsorption experiments were performed to investigate the dominant resistance between external and internal mass transfer in simultaneous and sequential adsorption experiments. From the evolution of protein solution concentration with time, the external mass transfer coefficients determined were very low in simultaneous (7.1 10−7 and 1.1 10−7 m/s for BSA and ferritin respectively) and sequential (4.6 10−7 and 2.5 10−7 m/s for BSA and ferritin respectively) adsorption systems which is in agreement with the low agitation speed used. From the transient protein uptakes, the internal mass transfer was studied and the homogenous diffusion model applied provides a good predictability in single as well as in simultaneous and sequential adsorption experiments. The effective diffusion coefficients were determined in sequential (6.4 10−14 m2/s and 3.8 10−14 m2/s for BSA and ferritin respectively) and simultaneous (4.2 10−14 m2/s for both proteins) systems. In multi-component adsorption system, it was found that BSA was slowed down upon the presence of ferritin on mixture solutions contrarily to ferritin protein. This phenomenon, known as electrostatic coupling effect, indicates that diffusion of charged proteins in ion exchangers are not independent.

Inverted Transflection Spectroscopy of Live Cells Using Metallic Grating on Elevated Nanopillars.

Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes-including live biological cells-that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: ATR prisms are difficult to integrate with multiwell cell culture workflows, while metasurfaces suffer from a limited spectral range and small penetration depth into analytes. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated on top of elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as inverted transflection spectroscopy (ITS). The analytic power of ITS is established by measuring a wide range of protein concentrations in solution, with the limit of detection in the single-digit mg mL-1. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is used to characterize their adhesion kinetic.

Poly(glutamic acid)-Based Viscosity Reducers for Concentrated Formulations of a Monoclonal IgG Antibody.

Above a concentration threshold, the viscosity of solutions of proteins increases abruptly, which hampers the injectability of therapeutic formulations. Concentrations above 200 g/L are an ideal goal for subcutaneous application of antibodies. Molecular additives, such as amino acids (e.g., arginine) help decrease the viscosity, but they are used at concentrations as high as about 200 mmol/L. We addressed the question of whether poly(amino acids) could be more efficient than small molecular additives. We observed marked fluidification of a model therapeutic monoclonal antibody (mAb) solution by poly(d,l-glutamic acid) and poly(l-glutamic acid) derivatives added at concentrations of <6.5 g/L (i.e., a mAb/polymer chain molar ratio between 4:1 and 1:1 mol/mol). The bare poly(glutamate) parent chains were compared with polyethylene glycol-grafted chains as PEGylation is a common way to enhance stability. Viscosity could be decreased to ∼20 mPa s as compared to values of ∼100 mPa s in the absence of polymers at 200 g/L mAb. Formation of complexes between the mAb and the polyglutamates was characterized by capillary electrophoresis analysis in dilute solutions (1 g/L mAb) and by observation of phase separation at higher concentrations, suggesting tight association at about 2:1 mol/mol mAb/polymer. Altogether, these results show that polyglutamate derivatives hold an untapped potential as an excipient for fluidification of concentrated protein solutions.

The dynamics of PEG‐coated nanoparticles in concentrated protein solutions up to the molecular crowding range

AbstractPolymer‐coated nanoparticles are widely studied in the context of nanomedicine and it is therefore of utmost importance to understand not only how their structure but also how their colloidal dynamics are affected by physiologically relevant conditions. A characteristic feature of the cytosol of cells is the very high concentration of proteins among other matrix components, often termed macromolecular crowding. Here, the structure and colloidal dynamics of poly(ethylene glycol) (PEG)‐coated gold nanoparticles in the presence of bovine serum albumin (BSA) concentrations ranging from 0 to 265 mg/mL are studied with X‐ray photon correlation spectroscopy. For protein–nanoparticle mixtures with high BSA concentrations, comparable to intracellular levels, a significant deviation of the apparent viscosity from expectations for pure BSA solutions is found. The findings strongly indicate that the nanoscopic viscous properties of the dense protein solutions are significantly affected by the nanoparticles. At these high concentrations, the colloidal stability of the samples depends on the molecular weight of the coating PEG–ligand, whereas at lower concentrations no differences are observed.

In situ Fourier transform infrared-attenuated total reflection spectroscopy and modeling investigation of protein adsorption: Case of expanded bovine serum albumin on titanium dioxide anatase.

The purpose of this experimental and modeling research is to study the pH effect and to determine the surface coverage plus the adsorption constant (Ka) of bovine serum albumin (BSA) protein adsorbed on TiO2 anatase surface, respectively. In situ Fourier transform infrared-attenuated total reflection spectroscopy in a flow-through cell was used to study the BSA adsorption on porous TiO2 anatase films. The experiments were performed in water solution, under different pH values, at a concentration of 10-6 mol/l. Theoretically, we extended the two-state model, based on a system of coupled differential equations, by adding a desorption parameter Kd2, for unfolded state. The model was solved taking into account the adsorption (Ka), desorption (Kd1,2), transformation (Kf) coefficients, and the initial solution protein concentration (C0). The findings clearly illustrated that the solution pH drastically changed the behavior of BSA adsorption, whereas the mathematical analytical solutions allowed us to determine the native state (θ1), the unfolded state (θ2), and the full one (θ) surface coverages. Finally, a good application of the approximated model on the experimental work, expanded BSA adsorbed on TiO2 anatase at pH = 1.7, indicated a value of Ka = (408.36 ± 0.996) × 102 mol-1 l min-1.

Quartz Crystal Microbalance as a Predictive Tool for Drug-Material of Construction Interactions in Intravenous Protein Drug Administration

As a growing number of protein drug products are developed, formulation characterization is becoming important. An IgG drug product is tested at concentrations from 0.0001–0.1 mg/mL for adsorption behavior to polymer surfaces polyvinyl chloride (PVC) and polypropylene (PP) upon dilution in normal saline (NS) using quartz crystal microbalance with dissipation (QCM-D). The studies mimicked IgG antibody interaction during IV administration with polymeric surfaces within syringes, lines, and bags. Drug product was characterized with excipients, with focus on surfactant. Drug solutions were run over polymer-coated sensors to measure the adsorption behavior of the formulation with emphasis on the behavior of each of the formulation's components. Over 60 sensorgram data sets were correlated with assayed protein solution concentrations in mock NS-diluted infusions of drug product in the equivalent concentrations to QCM experiments to build a preliminary predictive model for determining fraction of drug and surfactant adsorbed and lost at the hydrophobic surface during administration. These results create a method for reliably and predictively estimating drug product adsorption behavior and protein drug dose loss on polymers at different protein drug concentrations.

Protein crystallization with DNA templates

Protein crystallization plays a significant role in three-dimensional structural analysis and protein purification. It is important to increase the crystallization efficiency, which is possible by adding heterogeneous templates in crystallization systems. DNA is biologically compatible and artificially designable polymer, which is easy to extract. In this study, single- and double-stranded DNA of precise sequences were designed and used as templates to promote protein crystallization of lysozyme and catalase. Influence of DNA, single-stranded DNA with 10, 20, 40 bases and double-stranded DNA with 10, 20, 40 base pairs, were investigated. The success rate of obtaining crystals of lysozyme and catalase in equal period was significantly improved with the addition of DNA comparing without templates added. Double-stranded DNA led to higher nucleation rate than that with single-stranded DNA. The promotion of nucleation was more obvious at low concentration of protein solution and with longer chain DNA templates. Crystal number and crystallization rate was enhanced with addition of long double-stranded DNA templates. All the results confirm that DNA is an effective polymer additive to enhance protein crystallization, especially for the application of the scarce protein crystallization.

Flow behavior of protein solutions in a lab-scale chromatographic system

A fluid dynamics model has been developed to describe flow behavior in a lab-scale chromatographic system dedicated for protein processing. The case study included a detailed analysis of elution pattern of a protein, which was a monoclonal antibody, glycerol, and their mixtures in aqueous solutions. Glycerol solutions mimicked viscous environment of the concentrated protein solutions. The model accounted for concentration dependences of solution viscosity and density, and dispersion anisotropy in the packed bed. It was implemented into a commercial computational fluid dynamics software using user-defined functions. The prediction efficiency was successfully verified by comparing the model simulations in the form of the concentration profiles and their variances with the corresponding experimental data. The contribution of the individual elements of the chromatographic system to protein band broadening was evaluated for different configurations: for the extra-column volumes in the absence of the chromatographic column, for the zero-length column without the packed bed and for the column containing the packed bed. The influence of the operating variables, including: the mobile phase flowrate, the type of the injection system, i.e., the injection loop capillary or the superloop, the injection volume and the length of the packed bed, on band broadening of the protein was determined under nonadsorbing conditions. For protein solutions having viscosity comparable with the mobile phase, the flow behavior either in the column hardware or in the injection system made major contributions to band broadening, which depended on the type of the injection system. For highly viscous protein solution, the flow behavior in the packed bed exerted a dominant influence on band broadening.

Effects of concentration by block freezing and vacuum evaporation on the physicochemical properties and digestibility of whey

ABSTRACT Whey is a source of protein of high nutritional value. In this work, the effects of block cryoconcentration assisted by centrifugation and vacuum evaporation on the physicochemical properties and in vitro digestibility of whey were determined. In vitro digestibility analysis was performed by evaluating the degrees of protein hydrolysis of the fresh, evaporated and cryoconcentrated whey protein samples from the third cycle. The results showed that the samples after the second and third cryoconcentration cycles had no significant differences in protein or lactose content. The in vitro digestibility analysis indicated that the protein obtained by cryoconcentration showed better gastrointestinal digestibility than that obtained by evaporation, with values of 68.2% and 55.4%, respectively. This study demonstrates that block cryoconcentration assisted by centrifugation is an efficient and novel technique that enables the preparation of concentrated protein solutions of high nutritional and biological value.

Aligned silver nanowires for plasmonically-enhanced fluorescence detection of photoactive proteins in wet and dry environment

We developed a method of aligning silver nanowires in a microchannel and fixing them to glass substrates via appropriate functionalization. The attachment of nanowires to the substrate is robust with no variation of their angles over minutes. Specific conjugation with photoactive proteins is observed using wide-field fluorescence imaging in real-time for highly concentrated protein solution, both in a microchannel and in a chip geometry. In the latter case we can detect the presence of the proteins in the dropcasted solution down to single proteins. The results point towards possible implementation of aligned silver nanowires as geometrically defined plasmonic fluorescence sensing platforms.

Probing Cage Relaxation in Concentrated Protein Solutions by X-Ray Photon Correlation Spectroscopy.

Diffusion of proteins on length scales of their size is crucial for understanding the machinery of living cells. X-ray photon correlation spectroscopy (XPCS) is currently the only way to access long-time collective diffusion on these length scales, but radiation damage so far limits the use in biological systems. We apply a new approach to use XPCS to measure cage relaxation in crowded α-crystallin solutions. This allows us to correct for radiation effects, obtain missing information on long time diffusion, and support the fundamental analogy between protein and colloid dynamical arrest.

Characterizing Transient Protein-Protein Interactions by Trp-Cys Quenching and Computer Simulations.

Transient protein-protein interactions occur frequently under the crowded conditions encountered in biological environments. Tryptophan-cysteine quenching is introduced as an experimental approach with minimal labeling for characterizing such interactions between proteins due to its sensitivity to nano- to microsecond dynamics on subnanometer length scales. The experiments are paired with computational modeling at different resolutions including fully atomistic molecular dynamics simulations for interpretation of the experimental observables and to gain molecular-level insights. This approach is applied to model systems, villin variants and the drkN SH3 domain, in the presence of protein G crowders. It is demonstrated that Trp-Cys quenching experiments can differentiate between overall attractive and repulsive interactions between different proteins, and they can discern variations in interaction preferences at different protein surface locations. The close integration between experiment and simulations also provides an opportunity to evaluate different molecular force fields for the simulation of concentrated protein solutions.

Understanding intermolecular structure and forces in concentrated protein solutions through multi-protein simulations and structure factor measurements

Understanding intermolecular structure and forces in concentrated protein solutions through multi-protein simulations and structure factor measurements

Drug Product Characterization of High Concentration Non-Aqueous Protein Powder Suspensions

High concentration protein formulations for subcutaneous injection represent a substantial number of development projects in the pharmaceutical industry. Such concentrated aqueous protein solutions face some specific challenges such as increased viscosity and aggregation propensity. Protein powder suspensions in non-aqueous vehicles could be an alternative providing lower viscosity than the respective aqueous solution. The choice of potential suspension vehicles is limited as traditional non-aqueous liquids, such as oils, show an inherent high viscosity. We studied suspensions prepared by dispersing spray-dried protein powder in different vehicles including sesame oil and medium chain triglycerides, as well as fluorinated and semifluorinated alkanes. We found, that semifluorinated alkanes enable formulations with high concentrations up to 280 mg/ml monoclonal antibody with a low viscosity of less than 10 mPa·s and low injection forces. The glide force of suspensions containing 210 mg/ml protein was not affected by the particle size of the spray-dried powders with medians ranging from 1 to 14 µm. In contrast, suspensions prepared with cryo-milled powder showed markedly higher viscosities and were not injectable at the same concentration. Protein powder suspensions were syringeable using a 25G needle. Vial filling using a peristaltic pump was possible and lead to a uniform filling. Sedimentation of the suspension was slow and does not lead to challenges upon vial filling during manufacturing or transfer of the suspension into syringes. Thus, we could show that dispersions of spray-dried protein powders in non-aqueous vehicles, such as semifluorinated alkanes, are a promising alternative to aqueous protein solutions at high concentrations.

Salt template tuning morphology and porosity of biomass-derived N-doped porous carbon with high redox-activation for efficient energy storage

In this work, N-doped porous carbon with effective Faraday reaction activation is fabricated by pyrolysis of egg white in air at high temperature using a mixed KCl and NaCl salt sealing strategy. The mechanism of the morphology and pores affecting the redox reaction are discussed in depth and the morphology and porosity of the carbon product are regulated by adding different amounts of saturated NaCl salt solution to egg white before cooking in a water bath. The increasing amounts of saturated NaCl salt solution added to egg white can enable more salt particles to penetrate into carbon framework at high temperature due to the interaction between water molecules and salt particles, leading to the achievement of N-doped porous carbon with thin sheet and mesopore structure. The sheets and mesopores can accelerate the reaction kinetics involved with fast Faraday reaction and diffusion-controlled process by providing more electron and ion transfer expressways, producing the effective Faraday effects of carbon electrodes. Therefore, explored the supercapacitor applications, as-synthesized N-doped porous carbon is exhibited a superb three-electrode specific capacitance of 304 F g−1 at 1 A g −1. The symmetrical surpercapacitors are also displayed a high specific capacitance of 248 F g−1 at 1 A g −1 and a good cycling stability with 98.7% of initial capacitance retention rate undergoing 15 000 cycles at 2.5 A g−1. This work has fundamental merits for the use of the sustainable abandoned eggs and concentrated protein solution feedstocks to prepare carbon electrode materials and further expands the application field of the salt sealing technique.

Needle clogging of protein solutions in prefilled syringes: A two-stage process with various determinants

Clogging of staked-in-needle prefilled syringes (PFS) is a sporadic and scarcely predictable event, which occurs particularly in highly concentrated protein solutions and can result in the injection of incomplete doses, especially if autoinjector devices are used for administration. A systematic screening of possible causes and triggers was performed in order to find the crucial factors of influence, the underlying mechanisms and possible measures for prevention. An essential prerequisite for the formation of a solidified clog in the needle is the ingress of liquid from the barrel, which was investigated and quantified by means of neutron imaging after storage of prefilled syringes under various conditions. The needle filling ratio increases with both the storage temperature and the storage period, as a result of atmospheric gas diffusion through the needle shield. While the air pocket in the needle is reduced by this process, diffusion of water vapor does not affect the filling ratio but instead increases the protein concentration in the needle lumen, leading to an exponential rise of the viscosity and finally to the solidification of the protein solution. Maintaining the air pocket in the needle by avoiding any diffusion promoting pressure gradient is therefore the most effective protection from clogging.

Rheological characterization of β-lactoglobulin/lactoferrin complex coacervates

Heteroprotein complex coacervation between lactoferrin (LF) and β-lactoglobulin (β-LG), two oppositely charged proteins from whey, occurred under specific conditions of pH, ionic strength and protein molar ratio. The present work aims at characterizing the rheological properties of the concentrated phase called coacervate obtained after phase separation. Unlike some polysaccharide/protein coacervates, β-LG/LF heteroprotein coacervates exhibit a liquid-like behavior; the loss modulus G” being 100 times higher than the storage modulus G’ at low frequencies. This behavior was confirmed under creep-recovery tests. The heteroprotein coacervates exhibited a Newtonian viscous flow under low shear rate and a shear thinning behavior above 10 s−1. The coacervates are exceptionally viscous, reaching a viscosity value of 55 ± 10 Pa.s which is ∼2500 times higher than that measured on individual protein solutions of equivalent total concentration. Also, a structural change occurred in the coacervates, probably due to the weaknesses of electrostatic interactions inside the protein network at high shear rates. The observed time-dependent structural rearrangement was proved to be reversible. These findings open new ways for the use of coacervates as texturizing agents in food matrices.

APPLICATION OF SUPER-CROSSLINKED POLYMERS AS CARRIERS OF HETEROGENEOUS BIOCATALYSTS FOR INULINHYDROLYSIS REACTION

n this work the study of adsorption immobilization of inulinase on super-crosslinked macroporous sorbents based on styrene and divinylbenzene: low-base anion exchanger A100, high-base anion exchanger A500R, strong acid cation exchanger C100H was carried out. The influence of the duration of the sorption process, the value of the concentration of hydrogen ions and the concentration of protein in solution on the amount of immobilized enzyme and the activity of the obtained heterogeneous biocatalysts is considered. It was revealed that adsorption reaches its max-imum value on average after 4 h at pH of 4.7-5.0 for the sorbents under consideration. The activity of the obtained heterogeneous biocatalysts is 64.8-83.5% of the activity of free inulinase. Although the activity of inulinase during adsorption on the polymer carriers used in the work decreases, the integral amount of the resulting product will be higher than for the native catalyst.The isotherms of inulinase adsorption on super-crosslinked polymers have been studied. The high stability of the obtained heterogeneous biocatalysts is explained by the high sorption capacity of super-crosslinkedsorbents. It was revealed that immobilized inulinase can be used during 8-11 consecutive cycles of the substrate hydrolysis reaction.Using the BET adsorption theory, the enzyme sorption isotherms were analyzed and the equilibrium sorption parameters werecalculated: the maximum amount of sorbed inulinase, the constants characterizing the sorbate-sorbent and sorbate-sorbate interaction. Among the considered carriers, the highest value of the sorption equilibrium constant (KL=4.25±0.04 l/mmol) corresponds to the inulinase-cation exchanger biocatalyst, the sorption ca-pacity of which is also the largest. The data obtained is of interest for evaluating the effectiveness of the use of sorbents as inulinase carriers in subsequent technological operations of processing of inulin-containing raw materials.