Preferential exclusion of sucrose from recombinant interleukin-1 receptor antagonist: role in restricted conformational mobility and compaction of native state

Chemometrics in Protein Formulation: Stability Governed by Repulsion and Protein Unfolding

Therapeutic proteins can be challenging to develop due to their complexity and the requirement of an acceptable formulation to ensure patient safety and efficacy. To date, there is no universal formulation development strategy that can identify optimal formulation conditions for all types of proteins in a fast and reliable manner. In this work, high-throughput characterization, employing a toolbox of five techniques, was performed on 14 structurally different proteins formulated in 6 different buffer conditions and in the presence of 4 different excipients. Multivariate data analysis and chemometrics were used to analyze the data in an unbiased way. First, observed changes in stability were primarily determined by the individual protein. Second, pH and ionic strength are the two most important factors determining the physical stability of proteins, where there exists a significant statistical interaction between protein and pH/ionic strength. Additionally, we developed prediction methods by partial least-squares regression. Colloidal stability indicators are important for prediction of real-time stability, while conformational stability indicators are important for prediction of stability under accelerated stress conditions at 40 °C. In order to predict real-time storage stability, protein-protein repulsion and the initial monomer fraction are the most important properties to monitor.

A systematic review of commercial high concentration antibody drug products approved in the US: formulation composition, dosage form design and primary packaging considerations

Three critical aspects that define high concentration antibody products (HCAPs) are as follows: 1) formulation composition, 2) dosage form, and 3) primary packaging configuration. HCAPs have become successful in the therapeutic sector due to their unique advantage of allowing subcutaneous self-administration. Technical challenges, such as physical and chemical instability, viscosity, delivery volume limitations, and product immunogenicity, can hinder successful development and commercialization of HCAPs. Such challenges can be overcome by robust formulation and process development strategies, as well as rational selection of excipients and packaging components. We compiled and analyzed data from US Food and Drug Administration-approved and marketed HCAPs that are ≥100 mg/mL to identify trends in formulation composition and quality target product profile. This review presents our findings and discusses novel formulation and processing technologies that enable the development of improved HCAPs at ≥200 mg/mL. The observed trends can be used as a guide for further advancements in the development of HCAPs as more complex antibody-based modalities enter biologics product development.

Protein Engineering and HDX Identify Structural Regions of G-CSF Critical to Its Stability and Aggregation

The protein engineering and formulation of therapeutic proteins for prolonged shelf-life remain a major challenge in the biopharmaceutical industry. Understanding the influence of mutations and formulations on the protein structure and dynamics could lead to more predictive approaches to their improvement. Previous intrinsic fluorescence analysis of the chemically denatured granulocyte colony-stimulating factor (G-CSF) suggested that loop AB could subtly reorganize to form an aggregation-prone intermediate state. Hydrogen deuterium exchange mass spectrometry (HDX-MS) has also revealed that excipient binding increased the thermal unfolding transition midpoint (T_m) by stabilizing loop AB. Here, we have combined protein engineering with biophysical analyses and HDX-MS to reveal that increased exchange in a core region of the G-CSF comprising loop AB (ABI, a small helix, ABII) and loop CD packed onto helix B and the beginning of loop BC leads to a decrease in T_m and higher aggregation rates. Furthermore, some mutations can increase the population of the aggregation-prone conformation within the native ensemble, as measured by the greater local exchange within this core region.

Influence of the compatible solute sucrose on thylakoid membrane organization and violaxanthin de-epoxidation

The compatible solute sucrose reduces the efficiency of the enzymatic de-epoxidation of violaxanthin, probably by a direct effect on the protein parts of violaxanthin de-epoxidase which protrude from the lipid phase of the thylakoid membrane. The present study investigates the influence of the compatible solute sucrose on the violaxanthin cycle of higher plants in intact thylakoids and in in vitro enzyme assays with the isolated enzyme violaxanthin de-epoxidase at temperatures of 30 and 10 °C, respectively. In addition, the influence of sucrose on the lipid organization of thylakoid membranes and the MGDG phase in the in vitro assays is determined. The results show that sucrose leads to a pronounced inhibition of violaxanthin de-epoxidation both in intact thylakoid membranes and the enzyme assays. In general, the inhibition is similar at 30 and 10 °C. With respect to the lipid organization only minor changes can be seen in thylakoid membranes at 30 °C in the presence of sucrose. However, sucrose seems to stabilize the thylakoid membranes at lower temperatures and at 10 °C a comparable membrane organization to that at 30 °C can be observed, whereas control thylakoids show a significantly different membrane organization at the lower temperature. The MGDG phase in the in vitro assays is not substantially affected by the presence of sucrose or by changes of the temperature. We conclude that the presence of sucrose and the increased viscosity of the reaction buffers stabilize the protein part of the enzyme violaxanthin de-epoxidase, thereby decreasing the dynamic interactions between the catalytic site and the substrate violaxanthin. This indicates that sucrose interacts with those parts of the enzyme which are accessible at the membrane surface of the lipid phase of the thylakoid membrane or the MGDG phase of the in vitro enzyme assays.

Aggregation of protein therapeutics enhances their immunogenicity: causes and mitigation strategies

Protein aggregation in biotherapeutics has been identified to increase immunogenicity, leading to immune-mediated adverse effects, such as severe allergic responses including anaphylaxis. The induction of anti-drug antibodies (ADAs) moreover enhances drug clearance rates, and can directly block therapeutic function. In this review, identified immune activation mechanisms triggered by protein aggregates are discussed, as well as physicochemical properties of aggregates, such as size and shape, which contribute to immunogenicity. Furthermore, factors which contribute to protein stability and aggregation are considered. Lastly, with these factors in mind, we encourage an innovative and multidisciplinary approach with regard to further research in the field, with the overall aim to avoid immunogenic aggregation in future drug development.

Three-level hybrid modeling for systematic optimization of biocatalytic synthesis: α-glucosyl glycerol production by enzymatic trans-glycosylation from sucrose

Mechanism-based kinetic models are rigorous tools to analyze enzymatic reactions, but their extension to actual conditions of the biocatalytic synthesis can be difficult. Here, we demonstrate (mechanistic-empirical) hybrid modeling for systematic optimization of the sucrose phosphorylase-catalyzed glycosylation of glycerol from sucrose, to synthesize the cosmetic ingredient α-glucosyl glycerol (GG). The empirical model part was developed to capture nonspecific effects of high sucrose concentrations (up to 1.5 M) on microscopic steps of the enzymatic trans-glycosylation mechanism. Based on verified predictions of the enzyme performance under initial rate conditions (Level 1), the hybrid model was expanded by microscopic terms of the reverse reaction to account for the full-time course of GG synthesis (Level 2). Lastly (Level 3), the application of the hybrid model for comprehensive window-of-operation analysis and constrained optimization of the GG production (~250 g/L) was demonstrated. Using two candidate sucrose phosphorylases (from Leuconostoc mesenteroides and Bifidobacterium adolescentis), we reveal the hybrid model as a powerful tool of "process decision making" to guide rational selection of the best-suited enzyme catalyst. Our study exemplifies a closing of the gap between enzyme kinetic models considered for mechanistic research and applicable in technologically relevant reaction conditions; and it highlights the important benefit thus realizable for biocatalytic process development.

Manufacturing Challenges and Rational Formulation Development for AAV Viral Vectors

Adeno-associated virus (AAV) has emerged as a leading platform for gene delivery for treating various diseases due to its excellent safety profile and efficient transduction to various target tissues. However, the large-scale production and long-term storage of viral vectors is not efficient resulting in lower yields, moderate purity, and shorter shelf-life compared to recombinant protein therapeutics. This review provides a comprehensive analysis of upstream, downstream and formulation unit operation challenges encountered during AAV vector manufacturing, and discusses how desired product quality attributes can be maintained throughout product shelf-life by understanding the degradation mechanisms and formulation strategies. The mechanisms of various physical and chemical instabilities that the viral vector may encounter during its production and shelf-life because of various stressed conditions such as thermal, shear, freeze-thaw, and light exposure are highlighted. The role of buffer, pH, excipients, and impurities on the stability of viral vectors is also discussed. As such, the aim of this review is to outline the tools and a potential roadmap for improving the quality of AAV-based drug products by stressing the need for a mechanistic understanding of the involved processes.

Single-Use Capture Purification of Adeno-Associated Viral Gene Transfer Vectors by Membrane-Based Steric Exclusion Chromatography

We present membrane-based steric exclusion chromatography (SXC) as a universal capture step for purification of adeno-associated virus (AAV) gene transfer vectors independent of their serotype and surface characteristics. SXC is performed by mixing an unpurified cell culture supernatant containing AAV particles with polyethylene glycol (PEG) and feeding the mixture onto a chromatography filter unit. The purified AAV particles are recovered by flushing the unit with a solution lacking PEG. SXC is an inexpensive single-use method that permits to concentrate, purify, and re-buffer AAV particles with yields >95% and >80% impurity clearance. SXC could theoretically be employed at industrial scales with units of nearly 20 m².

Protecting thermodynamic stability of protein: The basic paradigm against stress and unfolded protein response by osmolytes

Organic osmolytes are known to play important role in stress protection by stabilizing macromolecules and suppressing harmful effects on functional activity. There is existence of several reports in the literature regarding their effects on structural, functional and thermodynamic aspects of many enzymes and the interaction parameters with proteins have been explored. Osmolytes are compatible with enzyme function and therefore, can be accumulated up to several millimolar concentrations. From the thermodynamic point of view, osmolyte raises mid-point of thermal denaturation (T_m) of proteins while having no significant effect on ΔG_D° (free energy change at physiological condition). Unfavorable interaction with the peptide backbone due to preferential hydration is the major driving force for folding of unfolded polypeptide in presence of osmolyte. However, the thermodynamic basis of stress protection and origin of compatibility paradigm has been a debatable issue. In the present manuscript, we attempt to elaborate the origin of stress protection and compatibility paradigm of osmolytes based on the effect on thermodynamic stability of proteins. We also infer that protective effects of osmolytes on ΔG_D° (of proteins) could also indicate its potential involvement in unfolded protein response and overall stress biology on macromolecular level.

Identification of Key Excipients for the Solubilization and Structural Characterization of Lipoprotein Lipase, An Enzyme for Hydrolysis of Triglyceride

Lipoprotein lipase (LPL) is an essential enzyme that hydrolyzes triglycerides in chylomicrons and very low-density lipoprotein into glycerol and fatty acids. One major hurdle in using LPL as a therapeutic has been its poor solubility/stability after purification. Solutions used to preserve purified LPL commonly contain either heparin, or concentrated glycerol and sodium chloride, resulting in hypertonic solutions. These solutions are not acceptable as pharmaceutical formulations. This paper describes the identification of a key excipient, sodium laurate, which can solubilize LPL in an isotonic environment without heparin or concentrated glycerol. A follow-up multi-variant study was performed to identify the effect of sodium laurate and its interaction with sodium chloride on the solubility and processing conditions of LPL. The LPL concentration (up to 14 mg/mL) achievable in pharmaceutically relevant and salt-free conditions was identified to be closely correlated to the concentration of sodium laurate, which was co-concentrated with LPL. The result that sodium laurate increases stability of LPL characterized by differential scanning calorimetry and UV absorbance spectra suggests that the mechanism of solubilization of LPL by sodium laurate is related to LPL structural stabilization. The findings indicate that substrates and their enzymatic products can be strong stabilizers for other protein molecules.

Effects of Excipients on the Structure and Dynamics of Filgrastim Monitored by Thermal Unfolding Studies by CD and NMR Spectroscopy

Product excipients are used to confer a number of desirable properties on the drug substance to maintain or improve stability and facilitate drug delivery. This is especially important for products where the active pharmaceutical ingredient (API) is a recombinant protein. In this study, we aimed to determine if excipients and formulation conditions affect the structure and/or modulate the dynamics of the protein API of filgrastim products. Samples of uniformly labeled ¹⁵N-Met-granulocyte-colony stimulating factor (GCSF) were prepared at 100 μM (near formulation concentration) with various concentrations of individual components (polysorbate-20 and -80, sorbitol) and three pH values. Nuclear magnetic resonance (NMR) spectroscopy techniques were applied to measure chemical shift perturbation (CSP) to detect structural changes, and relaxation parameters (T ₁, T ₂, and heteronuclear Overhauser effect) were measured to probe the effects on protein backbone motions. In parallel, the same solution conditions were subjected to protein thermal unfolding studies monitored by circular dichroism spectropolarimetry (CD). Detergents (polysorbate-20 and 80) do not induce any observable changes on the protein structure and do not modify its dynamics at formulation concentration. Lowering pH to 4.0, a condition known to stabilize the conformation of filgrastim, as well as the addition of sorbitol produced changes of the fast motion dynamics in the nanosecond and picosecond timescale. NMR-derived order parameters, which measure the local conformational entropy of the protein backbone, show that lowering pH leads to a compaction of the four-helix bundle while the addition of sorbitol relaxes helices B and C, thereby reducing the mobility of loop CD. CSPs and measurements of protein dynamics via NMR-derived order parameters provide a description in structural and motional terms at an atomic resolution on how formulation components contribute to the stabilization of filgrastim products.

Viewing rare conformations of the β2 adrenergic receptor with pressure-resolved DEER spectroscopy

The β₂ adrenergic receptor (β₂AR) is an archetypal G protein coupled receptor (GPCR). One structural signature of GPCR activation is a large-scale movement (ca. 6 to 14 Å) of transmembrane helix 6 (TM6) to a conformation which binds and activates a cognate G protein. The β₂AR exhibits a low level of agonist-independent G protein activation. The structural origin of this basal activity and its suppression by inverse agonists is unknown but could involve a unique receptor conformation that promotes G protein activation. Alternatively, a conformational selection model proposes that a minor population of the canonical active receptor conformation exists in equilibrium with inactive forms, thus giving rise to basal activity of the ligand-free receptor. Previous spin-labeling and fluorescence resonance energy transfer experiments designed to monitor the positional distribution of TM6 did not detect the presence of the active conformation of ligand-free β₂AR. Here we employ spin-labeling and pressure-resolved double electron-electron resonance spectroscopy to reveal the presence of a minor population of unliganded receptor, with the signature outward TM6 displacement, in equilibrium with inactive conformations. Binding of inverse agonists suppresses this population. These results provide direct structural evidence in favor of a conformational selection model for basal activity in β₂AR and provide a mechanism for inverse agonism. In addition, they emphasize 1) the importance of minor populations in GPCR catalytic function; 2) the use of spin-labeling and variable-pressure electron paramagnetic resonance to reveal them in a membrane protein; and 3) the quantitative evaluation of their thermodynamic properties relative to the inactive forms, including free energy, partial molar volume, and compressibility.

HDX and In Silico Docking Reveal that Excipients Stabilize G-CSF via a Combination of Preferential Exclusion and Specific Hotspot Interactions

Assuring the stability of therapeutic proteins is a major challenge in the biopharmaceutical industry, and a better molecular understanding of the mechanisms through which formulations influence their stability is an ongoing priority. While the preferential exclusion effects of excipients are well known, the additional presence and impact of specific protein-excipient interactions have proven to be more elusive to identify and characterize. We have taken a combined approach of in silico molecular docking and hydrogen deuterium exchange-mass spectrometry (HDX-MS) to characterize the interactions between granulocyte colony-stimulating factor (G-CSF), and some common excipients. These interactions were related to their influence on the thermal-melting temperatures (T_m) for the nonreversible unfolding of G-CSF in liquid formulations. The residue-level interaction sites predicted in silico correlated well with those identified experimentally and highlighted the potential impact of specific excipient interactions on the T_m of G-CSF.

Attachment of Proteins to a Hydroxyl-Terminated Surface Eliminates the Stabilizing Effects of Polyols

The physics of proteins interacting with surfaces can differ significantly from those seen when the same proteins are free in bulk solution. As an example, we describe here the extent to which site-specific attachment to a chemically well-defined macroscopic surface alters the ability of several stabilizing and destabilizing cosolutes to modulate protein folding thermodynamics. We determined this via guanidinium denaturations performed in the presence of varying concentrations of cosolutes when proteins were either site-specifically attached to self-assembled monolayers on gold or free in bulk solution. Doing this we found that the extent to which guanidinium (a destabilizing Hofmeister cation), sulfate (a stabilizing Hofmeister anion), and urea (a neutral denaturant) alter the folding free energy remains indistinguishable whether proteins are surface-attached or free in bulk solution. In sharp contrast, however, neutral osmolytes sucrose and glycerol, which significantly stabilize proteins in bulk solution, do not measurably affect their stability when they are attached to a hydroxyl-terminated surface. In contrast, we recovered bulk solution-like stabilization when the attachment surface was instead carboxyl-terminated. It thus appears that chemistry-specific surface interactions can dramatically alter the way in which biomolecules interact with other components of the system.

Three-percent sucrose acts as a thermostabilizer for cell-adapted foot-and-mouth disease virus without any negative effect on viral growth

AIMS

As cell-adapted foot-and-mouth disease virus (FMDV) with H56R mutation in VP3 has reduced thermostability, this study aimed to investigate the effect of thermostabilizers on cell-adapted FMDV for vaccine production.

METHODS AND RESULTS

We examined the effect of 3% sucrose, 10% (or 25%) glycerol or 10% FBS on cell-adapted FMDV O/SKR/JC/2014, containing H56R mutation in VP3, as vaccine seed virus at -80, 4, 25 or 37°C for 2, 4 or 7 days. The stabilizing effect of 3% sucrose on O/SKR/JC/2014 was observed at 25, 37°C, and after repeated freeze-thaw cycles. Additionally, we tested the effect of 3% sucrose on the growth of FMDV or cells and did not observe any decrease in either viral growth or cell viability.

CONCLUSIONS

Our study showed the protective effect of 3% sucrose on FMDV infectivity at various temperatures; this virus stock in 3% sucrose could be used for infecting cells without the removal of sucrose.

SIGNIFICANCE AND IMPACT OF THE STUDY

We suggest that 3% sucrose-containing medium could be beneficial for the stable storage and transport of cell-adapted FMDV.

Modulation of the competition between renaturation and aggregation of lysozyme by additive mixtures

The effects of 17 kinds of additive mixtures have been studied on refolding and aggregation of a model protein, lysozyme. Most of the prepared mixtures were efficient in inhibiting aggregation of the protein, and, surprisingly, four novel additive mixtures, i.e., lactic acid: l-arginine, lactic acid: l-glutamine, choline chloride: lactic acid, and imidazolium salt: β-cyclodextrin as well as choline chloride: urea exhibited a more remarkable efficacy in suppressing aggregation. Among these, lactic acid: l-arginine was identified as the most efficient additive, and lactic acid: l-glutamine and choline chloride: lactic acid were inefficient to recover the enzyme activity. In contrast, choline chloride: ethylene glycol: imidazole, choline chloride: glycerol: imidazole, imidazole: betaine: ethylene glycol were found to be less effective mixtures in preventing enzyme aggregation. Totally, it was demonstrated that the protective effects of the mixtures were improved as their concentrations increased. The improvement was more remarkable for imidazolium salt: β-cyclodextrin and choline chloride: urea, where the denatured lysozyme was reactivated and recovered up to 85% of its initial activity by enhancing their concentrations from 1 to 5% (V/V). It is suggested that such solution additives may be further employed as artificial chaperones to assist protein folding and stability.

Improved lyophilization conditions for long-term storage of bacteriophages

Phage therapy is one of the promising alternatives to combat the increasing problem of antibiotic resistance. Lyophilization is used for the preparation of pharmaceutical products to improve their stability in long-term storage. The aim of this study was to improve the stability of lyophilized bacteriophages using different excipients. Three lytic bacteriophages Escherichia phage ECP311, Klebsiella phage KPP235 and Enterobacter phage ELP140 were subjected to lyophilization using six different excipients: glucose, sucrose, gelatin, mannitol, polyethylene glycol and sorbitol. The lyophilized phages were stored at 4 °C and 37 °C and rehydrated using biological saline to test their viability at 5 months interval up to 20 months. The results showed that the use of sucrose, gelatin and their combination was beneficial in maintaining the viability of phages post-lyophilization. When lyophilized phages were stored at 4 °C, their viability was maintained up to 20 months, but at 37 °C there was a reduction in activity after 10 months. This is one of the few studies to report the lyophilization of phage cocktails to have viability for up to 10 months. Our study identified promising lyophilization excipients to effectively lyophilize bacteriophages for pharmaceutical applications and long-term storage.

Crowder-Induced Conformational Ensemble Shift in Escherichia coli Prolyl-tRNA Synthetase

The effect of molecular crowding on the structure and function of Escherichia coli prolyl-transfer RNA synthetase (Ec ProRS), a member of the aminoacyl-transfer RNA synthetase family, has been investigated using a combined experimental and theoretical method. Ec ProRS is a multidomain enzyme; coupled-domain dynamics are essential for efficient catalysis. To gain insight into the mechanistic detail of the crowding effect, kinetic studies were conducted with varying concentrations and sizes of crowders. In parallel, spectroscopic and quantum chemical studies were employed to probe the "soft interactions" between crowders and protein side chains. Finally, the dynamics of the dimeric protein was examined in the presence of crowders using a long-duration (70 ns) classical molecular dynamic simulations. The results of the simulations revealed a shift in the conformational ensemble, which is consistent with the preferential exclusion of cosolutes. The "soft interactions" model of the crowding effect also explained the alteration in kinetic parameters. In summary, the study found that the effects of molecular crowding on both conformational dynamics and catalytic function are correlated in the multidomain Ec ProRS, an enzyme that is central to protein synthesis in all living cells. This study affirmed that large and small cosolutes have considerable impacts on the structure, dynamics, and function of modular proteins and therefore must be considered for stabilizing protein-based pharmaceuticals and industrial enzymes.

Cosolvent and Crowding Effects on the Temperature- and Pressure-Dependent Dissociation Process of the α/β-Tubulin Heterodimer

Tubulin is one of the main components of the cytoskeleton of eukaryotic cells. The formation of microtubules depends strongly on environmental and solution conditions, and has been found to be among the most pressure sensitive processes in vivo. We explored the effects of different types of cosolvents, such as trimethylamine-N-oxide (TMAO), sucrose and urea, and crowding agents to mimic cell-like conditions, on the temperature and pressure stability of the building block of microtubules, i. e. the α/β-tubulin heterodimer. To this end, fluorescence and FTIR spectroscopy, differential scanning and pressure perturbation calorimetry as well as fluorescence anisotropy and correlation spectroscopies were applied. The pressure and temperature of dissociation of α/β-tubulin as well as the underlying thermodynamic parameters upon dissociation, such as volume and enthalpy changes, have been determined for the different solution conditions. The temperature and pressure of dissociation of the α/β-tubulin heterodimer and hence its stability increases dramatically in the presence of TMAO and the nanocrowder sucrose. We show that by adjusting the levels of compatible cosolutes and crowders, cells are able to withstand deteriorating effects of pressure even up to the kbar-range.

Steric Repulsion Forces Contributed by PEGylation of Interleukin-1 Receptor Antagonist Reduce Gelation and Aggregation at the Silicone Oil-Water Interface

Silicone oil, used as a lubricating coating in pharmaceutical containers, has been implicated as a cause of therapeutic protein aggregation. After adsorbing to silicone oil-water interfaces, proteins may form interfacial gels, which can be transported into solution as insoluble aggregates if the interfaces are perturbed. Mechanical interfacial perturbation of both monomeric recombinant human interleukin-1 receptor antagonist (rhIL-1ra) and PEGylated rhIL-1ra (PEG rhIL-1ra) in siliconized syringes resulted in losses of soluble monomeric protein. However, the loss of rhIL-1ra was twice that for PEG rhIL-1ra; even though in solution, PEG rhIL-1ra had a lower ΔG_unf and exhibited a more perturbed tertiary structure at the interface. Net protein-protein interactions in solution for rhIL-1ra were attractive but increased steric repulsion because of PEGylation led to net repulsive interactions for PEG rhIL-1ra. Attractive interactions for rhIL-1ra were associated with increases in intermolecular β-sheet content at the interface, whereas no intermolecular β-sheet structures were observed for adsorbed PEG rhIL-1ra. rhIL-1ra formed interfacial gels that were 5 times stronger than those formed by PEG rhIL-1ra. Thus, the steric repulsion contributed by the PEGylation resulted in decreased interfacial gelation and in the reduction of aggregation, in spite of the destabilizing effects of PEGylation on the protein's conformational stability.

Protein-protein interactions controlling interfacial aggregation of rhIL-1ra are not described by simple colloid models

We investigated the effects of protein-protein interaction strength on interfacial viscoelastic properties and aggregation of recombinant human interleukin-1 receptor antagonist (rhIL-1ra) at silicone oil-water interfaces. Osmotic second virial coefficients determined by static light scattering were used to quantify protein-protein interactions in bulk solution. Attractive protein-protein interactions dominated at low ionic strengths and their magnitude decreased with increasing ionic strength, in contrast to repulsive interactions that would be expected based on uniformly charged sphere models. Interfacial shear rheometry was used to characterize rhIL-1ra interfacial layers. More attractive protein-protein interactions in bulk solution correlated with stronger interfacial gels. Thioflavin-T fluorescence measurements indicated that the intermolecular β-sheet content of rhIL-1ra incubated in the presence of silicone oil-water interfaces correlated with gel strength. Siliconized syringes were used to probe the effects of mechanical perturbation of the interfacial gel layers. When rhIL-1ra solutions in siliconized glass syringes were subjected to end-over-end rotation, monomeric rhIL-1ra was lost from solution, and particles containing aggregated protein were released into the bulk aqueous phase. The loss of monomeric rhIL-1ra in response to mechanical perturbation was highest under the conditions where the strongest gels were observed. Aggregation of rhIL-1ra was strictly interface-induced and growth of aggregates in the bulk solution was not observed, even in the presence of particles released from silicone oil-water interfaces.

Stabilization of RDT target antigens present in dried Plasmodium falciparum-infected samples for validating malaria rapid diagnostic tests at the point of care

BACKGROUND

Malaria rapid diagnostic tests (RDTs) are a great achievement in implementation of parasite based diagnosis as recommended by World Health Organization. A major drawback of RDTs is lack of positive controls to validate different batches/lots at the point of care. Dried Plasmodium falciparum-infected samples with the RDT target antigens have been suggested as possible positive control but their utility in resource limited settings is hampered by rapid loss of activity over time.

METHODS

This study evaluated the effectiveness of chemical additives to improve long term storage stability of RDT target antigens (HRP2, pLDH and aldolase) in dried P. falciparum-infected samples using parasitized whole blood and culture samples. Samples were treated with ten selected chemical additives mainly sucrose, trehalose, LDH stabilizer and their combinations. After baseline activity was established, the samples were air dried in bio-safety cabinet and stored at room temperatures (~ 25 °C). Testing of the stabilized samples using SD Bioline, BinaxNOW, CareStart, and First Response was done at intervals for 53 weeks.

RESULTS

Stability of HRP2 at ambient temperature was reported at 21-24 weeks while that of PAN antigens (pLDH and aldolase) was 2-18 weeks of storage at all parasite densities. The ten chemical additives increased the percentage stability of HRP2 and PAN antigens. Sucrose alone and its combinations with Alsever's solution or biostab significantly increased stability of HRP2 by 56% at 2000 p/µL (p < 0.001). Trehalose and its combinations with biostab, sucrose or glycerol significantly increased stability of HRP2 by 57% (p < 0.001). Unlike sucrose, the stability of the HRP2 was significantly retained by trehalose at lower concentrations (500, and 200 p/µL). Trehalose in combination biostab stabilizer increased the percentage stability of PAN antigens by 42, and 32% at 2000 and 500 p/µL respectively (p < 0.01). This was also the chemical combination with the shortest reconstitution time (~ < 20 min).

CONCLUSIONS

These findings confirm that stabilizing RDT target antigens in dried P. falciparum-infected samples using chemical additives provides field-stable positive controls for malaria RDTs.

Predicting Protein-Protein Interactions of Concentrated Antibody Solutions Using Dilute Solution Data and Coarse-Grained Molecular Models

Protein-protein interactions for solutions of an IgG1 molecule were quantified using static light scattering (SLS) measurements from low to high protein concentrations (c₂). SLS was used to determine second osmotic virial coefficients (B₂₂) at low c₂, and excess Rayleigh profiles (R^ex/K vs. c₂) and zero-q structure factors (S_q=0) as a function of c₂ at higher c₂ for a series of conditions (pH, sucrose concentration, and total ionic strength [TIS]). Repulsive (attractive) interactions were observed at low TIS (high TIS) for pH 5 and 6.5, with increasing repulsions when 5% w/w sucrose was also present. Previously developed and refined coarse-grained antibody models were used to fit model parameters from B₂₂ versus TIS data. The resulting parameters from low-c₂ conditions were used as the sole input to multiprotein Monte Carlo simulations to predict high-c₂R^ex/K and S_q=0 behavior up to 150 g/L. Experimental results at high-c₂ conditions were quantitatively predicted by the simulations for the coarse-grained models that treated antibody molecules as either 6 or 12 (sub) domains, which preserved the basic shape of a monoclonal antibody. Finally, preferential accumulation of sucrose around the protein surface was identified via high-precision density measurements, which self-consistently explained the simulation and experimental SLS results.

Development of a candidate stabilizing formulation for bulk storage of a double mutant heat labile toxin (dmLT) protein based adjuvant

This work describes the formulation design and development of a novel protein based adjuvant, a double mutant of heat labile toxin (dmLT), based on knowledge of the protein's structural integrity and physicochemical degradation pathways. Various classes of pharmaceutical excipients were screened for their stabilizing effect on dmLT during exposure to thermal and agitation stresses as monitored by high throughput analytical assays for dmLT degradation. Sucrose, phosphate, sodium chloride, methionine and polysorbate-80 were identified as potential stabilizers that protected dmLT against either conformational destabilization, aggregation/particle formation or chemical degradation (e.g., Met oxidation and Lys glycation). Different combinations and concentrations of the selected stabilizers were then evaluated to further optimize dmLT stability while maintaining pharmaceutically acceptable ranges of solution pH and osmolality. The effect of multiple freeze-thaw (FT) cycles on the physical stability of candidate bulk formulations was also examined. Increasing the polysorbate-80 concentration to 0.1% in the lead candidate bulk formulation mitigated the loss of protein mass during FT. This formulation development study enabled the design of a new bulk formulation of the dmLT adjuvant and provides flexibility for future use in combination with a variety of different vaccine dosage forms with different antigens.

Osmolyte-Like Stabilizing Effects of Low GdnHCl Concentrations on d-Glucose/d-Galactose-Binding Protein

The ability of d-glucose/d-galactose-binding protein (GGBP) to reversibly interact with its ligands, glucose and galactose, makes this protein an attractive candidate for sensing elements of glucose biosensors. This potential is largely responsible for attracting researchers to study the conformational properties of this protein. Previously, we showed that an increase in the fluorescence intensity of the fluorescent dye 6-bromoacetyl-2-dimetylaminonaphtalene (BADAN) is linked to the holo-form of the GGBP/H152C mutant in solutions containing sub-denaturing concentrations of guanidine hydrochloride (GdnHCl). It was hypothesized that low GdnHCl concentrations might lead to compaction of the protein, thereby facilitating ligand binding. In this work, we utilize BADAN fluorescence spectroscopy, intrinsic protein UV fluorescence spectroscopy, and isothermal titration calorimetry (ITC) to show that the sub-denaturing GdnHCl concentrations possess osmolyte-like stabilizing effects on the structural dynamics, conformational stability, and functional activity of GGBP/H152C and the wild type of this protein (wtGGBP). Our data are consistent with the model where low GdnHCl concentrations promote a shift in the dynamic distribution of the protein molecules toward a conformational ensemble enriched in molecules with a tighter structure and a more closed conformation. This promotes the increase in the configurational complementarity between the protein and glucose molecules that leads to the increase in glucose affinity in both GGBP/H152C and wtGGBP.

Solution pH jump during antibody and Fc-fusion protein thaw leads to increased aggregation

Freeze-thaw cycles impact the amount of aggregation observed in antibodies and Fc-fusion proteins. Various formulation strategies are used to mitigate the amount of aggregation that occurs upon putting a protein solution through a freeze-thaw cycle. Additionally, low pH solutions cause native antibodies to unfold, which are prone to aggregate upon pH neutralization. There is great interest in the mechanism that causes therapeutic proteins to aggregate since aggregate species can cause unwanted immunogenicity in patients. Herein, an increase in aggregation is reported when the pH is adjusted from pH 3 up to a pH ranging from pH 4 to pH 7 during the thaw process of a frozen antibody solution. Raising the pH during the thaw process caused a significant increase in the percent aggregation observed. Two antibodies and one Fc-fusion protein were evaluated during the pH jump thaw process and similar effects were observed. The results provide a new tool to study the kinetics of therapeutic protein aggregation upon pH increase.

Elucidating the weak protein-protein interaction mechanisms behind the liquid-liquid phase separation of a mAb solution by different types of additives

Liquid-liquid phase separation (LLPS) has long been observed during the physical stability investigation of therapeutic protein formulations. The buffer conditions and the presence of various excipients are thought to play important roles in the formulation development of monoclonal antibodies (mAbs). In this study, the effects of several small-molecule excipients (histidine, alanine, glycine, sodium phosphate, sodium chloride, sorbitol and sucrose) with diverse physical-chemical properties on LLPS of a model IgG1 (JM2) solutions were investigated by multiple techniques, including UV-vis spectroscopy, circular dichroism, differential scanning calorimetry/fluorimetry, size exclusion chromatography and dynamic light scattering. The LLPS of JM2 was confirmed to be a thermodynamic equilibrium process with no structural changes or irreversible aggregation of proteins. Phase diagrams of various JM2 formulations were constructed, suggesting that the phase behavior of JM2 was dependent on the solution pH, ionic strength and the presence of other excipients such as glycine, alanine, sorbitol and sucrose. Furthermore, we demonstrated that for this mAb, the interaction parameter (k_D) determined at low protein concentration appeared to be a good predictor for the occurrence of LLPS at high concentration.

Influence of isoform-specific Ras lipidation motifs on protein partitioning and dynamics in model membrane systems of various complexity

The partitioning of the lipidated signaling proteins N-Ras and K-Ras4B into various membrane systems, ranging from single-component fluid bilayers, binary fluid mixtures, heterogeneous raft model membranes up to complex native-like lipid mixtures (GPMVs) in the absence and presence of integral membrane proteins have been explored in the last decade in a combined chemical-biological and biophysical approach. These studies have revealed pronounced isoform-specific differences regarding the lateral distribution in membranes and formation of protein-rich membrane domains. In this context, we will also discuss the effects of lipid head group structure and charge density on the partitioning behavior of the lipoproteins. Moreover, the dynamic properties of N-Ras and K-Ras4B have been studied in different model membrane systems and native-like crowded milieus. Addition of crowding agents such as Ficoll and its monomeric unit, sucrose, gradually favors clustering of Ras proteins in forming small oligomers in the bulk; only at very high crowder concentrations association is disfavored.

Protein Partial Molar Volumes in Multicomponent Solutions from the Perspective of Inverse Kirkwood-Buff Theory

Inverse Kirkwood-Buff (KB) solution theory can be used to relate macroscopic quantities with molecular scale interactions and correlation functions, in the form of KB integrals. Protein partial specific volumes ([Formula: see text]) from high-precision density measurements can be used to quantify solvent-solute and solute-solute KB integrals. Currently, general expressions for [Formula: see text] as a function of cosolute concentration (c₃) have been provided for only binary and ternary solutions. We derive a general multicomponent expression for [Formula: see text] in terms of the relevant KB integrals for the case of low (infinite dilution) protein concentration but arbitrary cosolute concentrations. To test the utility of treating a quaternary system with a pseudoternary approximation, α-Chymotrypsinogen (aCgn) solutions with a series of solutes (NaCl, sucrose, and trehalose) were compared as a function of solute concentration with and without buffer present. Comparison between those ternary and quaternary solutions shows equivalent results within experimental uncertainty and suggests the pseudoternary approximation may be reasonable. In the case of aCgn, doing so also revealed that the preferential interactions can depend on pH. Analysis of steric contributions also provides an example that illustrates how KB integrals allow one to interpret [Formula: see text] in terms of contributions from molecular volume, excluded volume, and hydration/solvation effects.

Steric exclusion chromatography for purification of cell culture-derived influenza A virus using regenerated cellulose membranes and polyethylene glycol

Steric exclusion chromatography has been used for the purification of proteins and bacteriophages using monoliths. The operation is carried out by mixing a crude sample containing the target species with a predetermined concentration and molecular weight of polyethylene glycol (PEG) and loading it onto a non-reactive hydrophilic surface. Product capture occurs by the mutual steric exclusion of PEG between the product and the matrix. Selectivity is significantly influenced by target product size. Product elution is achieved by decreasing the PEG concentration. In this study, a 75cm² cellulose membrane adsorber was used for the purification of a clarified and inactivated influenza A virus broth produced in a 5L bioreactor using suspension Madin Darby canine kidney cells. Product recovery was above 95% based on hemagglutination activity and single radial immunodiffusion assays. Maximum depletion of double stranded host cell DNA and total protein was 99.7% and 92.4%, respectively. Purified virus particles showed no aggregation with a monodisperse peak around 84nm. 250mL of the clarified inactivated virus broth was purified within 40min. The surface area productivity based on the recovery of the viral hemagglutinin antigen was 28-50mgm^-2h^-1 depending on the feed and loading conditions.

Charge-mediated Fab-Fc interactions in an IgG1 antibody induce reversible self-association, cluster formation, and elevated viscosity

Concentration-dependent reversible self-association (RSA) of monoclonal antibodies (mAbs) poses a challenge to their pharmaceutical development as viable candidates for subcutaneous delivery. While the role of the antigen-binding fragment (Fab) in initiating RSA is well-established, little evidence supports the involvement of the crystallizable fragment (Fc). In this report, a variety of biophysical tools, including hydrogen exchange mass spectrometry, are used to elucidate the protein interface of such non-covalent protein-protein interactions. Using dynamic and static light scattering combined with viscosity measurements, we find that an IgG1 mAb (mAb-J) undergoes RSA primarily through electrostatic interactions and forms a monomer-dimer-tetramer equilibrium. We provide the first direct experimental mapping of the interface formed between the Fab and Fc domains of an antibody at high protein concentrations. Charge distribution heterogeneity between the positively charged interface spanning complementarity-determining regions CDR3H and CDR2L in the Fab and a negatively charged region in C_H3/Fc domain mediates the RSA of mAb-J. When arginine and NaCl are added, they disrupt RSA of mAb-J and decrease the solution viscosity. Fab-Fc domain interactions between mAb monomers may promote the formation of large transient antibody complexes that ultimately cause increases in solution viscosity. Our findings illustrate how limited specific arrangements of amino-acid residues can cause mAbs to undergo RSA at high protein concentrations and how conserved regions in the Fc portion of the antibody can also play an important role in initiating weak and transient protein-protein interactions.

Low-volume solubility assessment during high-concentration protein formulation development

OBJECTIVE

Solubility is often one of the limiting factors for high-concentration protein formulation (HCF) development. Determination of protein solubility is challenging and requires high amount of material. Therefore, low-volume and predictive approaches are desired.

METHODS

This work presents a simple and material-saving approach using static light scattering to describe non-ideal solution behaviour of HCF. Non-ideality can be related to protein-protein interactions in solution. The type and strength of these interactions indicate maximum protein solubility at actual formulation compositions. Interactions of four therapeutic model proteins at multiple formulation compositions were investigated, and deduced solubility was compared to apparent solubility behaviour determined by ether turbidity or content measurements.

KEY FINDINGS

Protein-protein interactions and deduced solubilities matched actual solubility data for all tested formulations. Protein solubility was found to be lowest at pH values near the isoelectric point of each model protein. Buffer salts and ionic strength were also found to strongly influence protein solubility. In addition, sucrose and a combination of arginine and glycine enhanced protein solubility, whereas surfactants such as polysorbate 20 did not influence protein solubility.

CONCLUSIONS

The introduced screening procedure is a powerful tool during (early) protein formulation development. It meets several requirements of HCF development and enables reliable prediction of protein solubility based on determination of protein interactions. In addition, rare data about the influence of several common excipients on apparent solubility of therapeutic proteins were shown.

Challenges with osmolytes as inhibitors of protein aggregation: Can nucleic acid aptamers provide an answer?

Protein aggregation follows some common motifs. Whether in the formation of inclusion bodies in heterologous overexpression systems or inclusions in protein conformational diseases, or aggregation during storage or transport of protein formulations, aggregates form cross beta-sheet structures and stain with amyloidophilic dyes like Thioflavin T and Congo Red, irrespective of the concerned protein. Traditionally, osmolytes are used to stabilize proteins against stress conditions. They are employed right from protein expression, through production and purification, to formulation and administration. As osmolytes interact with the solvent, the differential effect of the stress condition on the solvent mostly determines the effect of the osmolyte on protein stability. Nucleic acid aptamers, on the other hand, are highly specific for their targets. When selected against monomeric, natively folded proteins, they bind to them with very high affinity. This binding inhibits the unfolding of the protein and/or monomer-monomer interaction which are the initial common steps of protein aggregation. Thus, by changing the approach to a protein-centric model, aptamers are able to function as universal stabilizers of proteins. The review discusses cases where osmolytes were unable to provide stabilization to proteins against different stress conditions, a gap which the aptamers seem to be able to fill.

Relative Cosolute Size Influences the Kinetics of Protein-Protein Interactions

Protein signaling occurs in crowded intracellular environments, and while high concentrations of macromolecules are postulated to modulate protein-protein interactions, analysis of their impact at each step of the reaction pathway has not been systematically addressed. Potential cosolute-induced alterations in target association are particularly important for a signaling molecule like calmodulin (CaM), where competition among >300 targets governs which pathways are selectively activated. To explore how high concentrations of cosolutes influence CaM-target affinity and kinetics, we methodically investigated each step of the CaM-target binding mechanism under crowded or osmolyte-rich environments mimicked by ficoll-70, dextran-10, and sucrose. All cosolutes stabilized compact conformers of CaM and modulated association kinetics by affecting diffusion and rates of conformational change; however, the results showed that differently sized molecules had variable effects to enhance or impede unique steps of the association pathway. On- and off-rates were modulated by all cosolutes in a compensatory fashion, producing little change in steady-state affinity. From this work insights were gained on how high concentrations of inert crowding agents and osmolytes fit into a kinetic framework to describe protein-protein interactions relevant for cellular signaling.

Translational Dynamics of Lipidated Ras Proteins in the Presence of Crowding Agents and Compatible Osmolytes

Ras proteins are small GTPases and are involved in transmitting signals that control cell growth, differentiation, and proliferation. Since the cell cytoplasm is crowded with different macromolecules, understanding the translational dynamics of Ras proteins in crowded environments is crucial to yielding deeper insight into their reactivity and function. Herein, the translational dynamics of lipidated N-Ras and K-Ras4B is studied in the bulk and in the presence of a macromolecular crowder (Ficoll) and the compatible osmolyte and microcrowder sucrose by fluorescence correlation spectroscopy. The results reveal that N-Ras forms dimers due to the presence of its lipid moiety in the hypervariable region, whereas K-Ras4B remains in its monomeric form in the bulk. Addition of a macromolecular crowding agent gradually favors clustering of the Ras proteins. In 20 wt % Ficoll N-Ras forms trimers and K-Ras4B dimers. Concentrations of sucrose up to 10 wt % foster formation of N-Ras trimers and K-Ras dimers as well. The results can be rationalized in terms of the excluded-volume effect, which enhances the association of the proteins, and, for the higher concentrations, by limited-hydration conditions. The results of this study shed new light on the association state of these proteins in a crowded environment. This is of particular interest for the Ras proteins, because their solution state-monomeric or clustered-influences their membrane-partitioning behavior and their interplay with cytosolic interaction partners.

Protein stabilizer, NDSB-195, enhances the dynamics of the β4 -α2 loop of ubiquitin

Non-detergent sulfobetaines (NDSBs) are a new group of small, synthetic protein stabilizers, which have advantages over classical compatible osmolytes, such as polyol, amines, and amino acids: they do not increase solution viscosity, unlike polyols, and they are zwitterionic at all pH ranges, unlike amines and amino acids. NDSBs also facilitate the crystallization and refolding of proteins. The mechanism whereby NDSBs exhibit such activities, however, remains elusive. To gain insight into this mechanism, we studied, using nuclear magnetic resonance (NMR), the effects of dimethylethylammonium propane sulfonate (NDSB-195) on the dynamics of ubiquitin, on which a wealth of information has been accumulated. By analyzing the line width of amide proton resonances and the transverse relaxation rates of nitrogen atoms, we found that NDSB-195 enhances the microsecond-millisecond dynamics of a β4 -α2 loop of ubiquitin. Although those compounds that enhance protein dynamics are generally considered to destabilize protein molecules, NDSB-195 enhanced the stability of ubiquitin against guanidium chloride denaturation. Thus, the simultaneous enhancement of stability and flexibility by a single compound can be attained.

Hofmeister Ion-Induced Changes in Water Structure Correlate with Changes in Solvation of an Aggregated Protein Complex

RecA is a naturally aggregating Escherichia coli protein that catalyzes the strand exchange reaction utilized in DNA repair. Previous studies have shown that the presence of salts influence RecA activity, aggregation, and stability and that salts stabilize RecA in an inverse-anionic Hofmeister series. Here we utilized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and circular dichroism (CD) to investigate how various Hofmeister salts alter the water structure and RecA solvation and aggregation. Spectroscopic studies performed in water and deuterium oxide suggest that salts alter water O-(1)H and O-(2)H stretch and bend vibrations as well as protein amide I (or I') and amide II (or II') vibrations. Anions have a much larger influence on water vibrations than cations. Water studies also show increased water-water and/or water-ion interactions in the presence of strongly hydrated SO4(2-) salts and evidence for decreased interactions with weakly hydrated Cl(-) and ClO4(-) salts. Salt-water difference infrared spectra show that kosmotropic salts are more hydrated than chaotropic salts. Interestingly, this is the opposite trend to the changes in protein solvation. Infrared spectra of RecA show that vibrations associated with protein desolvation were observed in the presence of SO4(2-) salts. Conversely, vibrations associated with protein solvation were observed in the presence of Cl(-) and ClO4(-) salts. Difference infrared studies on the dehydration of model proteins aided in identifying changes in RecA-solvent interactions. This study provides evidence that salt-induced changes in water vibrations correlate to changes in protein solvent interactions and thermal stability.

Effect of Short Chain Poly(ethylene glycol)s on the Hydration Structure and Dynamics around Human Serum Albumin

We report the changes in the hydration dynamics around a globular protein, human serum albumin (HSA), in the presence of two short chain crowding agents, namely poly(ethylene glycol)s (PEG 200 and 400). The change in the network water structure is investigated using FTIR spectroscopy in the far-infrared (FIR) frequency range. Site specific changes are obtained by time-resolved fluorescence spectroscopic technique using the intrinsic fluorophore tryptophan (Trp214) of HSA. The collective hydration dynamics of HSA in the presence of PEG molecules are obtained using terahertz (THz) time domain spectroscopy (TTDS) and high intensity p-Ge THz measurements. Our study affirms a considerable perturbation of HSA hydration beyond a critical concentration of PEG.

Influence of trehalose on human islet amyloid polypeptide fibrillation and aggregation

A lower dose of trehalose inhibits or delays, while higher dose of trehalose promotes the hIAPP fibrillation and aggregation.

Structural Changes and Aggregation Mechanisms for Anti-Streptavidin IgG1 at Elevated Concentration

Non-native protein aggregation may occur during manufacturing and storage of protein therapeutics, and this may decrease drug efficacy or jeopardize patient safety. From a regulatory perspective, changes in higher order structure due to aggregation are of particular interest but can be difficult to monitor directly at elevated protein concentrations. The present report focuses on non-native aggregation of antistreptavidin (AS) IgG1 at 30 mg/mL under solution conditions that prior work at dilute concentrations (e.g., 1 mg/mL) indicated would result in different aggregation mechanisms. Time-dependent aggregation and structural changes were monitored in situ with dynamic light scattering, small-angle neutron scattering, and Raman scattering and ex situ with far-UV circular dichroism and second-derivative UV spectroscopy. The effects of adding 0.15 M (∼5 w/w %) sucrose were also assessed. The addition of sucrose decreased monomer loss rates but did not change protein-protein interactions, aggregation mechanism(s), or aggregate structure and morphology. Consistent with prior results, altering the pD or salt concentration had the primary effect of changing the aggregation mechanism. Overall, the results provide a comparison of aggregate structure and morphology created via different growth mechanisms using orthogonal techniques and show that the techniques agree at least qualitatively. Interestingly, AS-IgG1 aggregates created at pD 5.3 with no added salt formed the smallest aggregates but had the largest structural changes compared to other solution conditions. The observation that the larger aggregates were also those with less structural perturbation compared to folded AS-IgG1 might be expected to extend to other proteins if the same strong electrostatic repulsions that mediate aggregate growth also mediate structural changes of the constituent proteins within aggregates.

Structural and functional stabilization of protein entities: state-of-the-art

Within the context of biomedicine and pharmaceutical sciences, the issue of (therapeutic) protein stabilization assumes particular relevance. Stabilization of protein and protein-like molecules translates into preservation of both structure and functionality during storage and/or targeting, and such stabilization is mostly attained through establishment of a thermodynamic equilibrium with the (micro)environment. The basic thermodynamic principles that govern protein structural transitions and the interactions of the protein molecule with its (micro)environment are, therefore, tackled in a systematic fashion. Highlights are given to the major classes of (bio)therapeutic molecules, viz. enzymes, recombinant proteins, (macro)peptides, (monoclonal) antibodies and bacteriophages. Modification of the microenvironment of the biomolecule via multipoint covalent attachment onto a solid surface followed by hydrophilic polymer co-immobilization, or physical containment within nanocarriers, are some of the (latest) strategies discussed aiming at full structural and functional stabilization of said biomolecules.

Effect of viscogens on the kinetic response of a photoperturbed allosteric protein

By covalently binding a photoswitchable linker across the binding groove of the PDZ2 domain, a small conformational change can be photo-initiated that mimics the allosteric transition of the protein. The response of its binding groove is investigated with the help of ultrafast pump-probe IR spectroscopy from picoseconds to tens of microseconds. The temperature dependence of that response is compatible with diffusive dynamics on a rugged energy landscape without any prominent energy barrier. Furthermore, the dependence of the kinetics on the concentration of certain viscogens, sucrose, and glycerol, has been investigated. A pronounced viscosity dependence is observed that can be best fit by a power law, i.e., a fractional viscosity dependence. The change of kinetics when comparing sucrose with glycerol as viscogen, however, provides strong evidence that direct interactions of the viscogen molecule with the protein do play a role as well. This conclusion is supported by accompanying molecular dynamics simulations.

Preferential Interactions and the Effect of Protein PEGylation

Background

PEGylation is a strategy used by the pharmaceutical industry to prolong systemic circulation of protein drugs, whereas formulation excipients are used for stabilization of proteins during storage. Here we investigate the role of PEGylation in protein stabilization by formulation excipients that preferentially interact with the protein.

Methodology/Principal Findings

The model protein hen egg white lysozyme was doubly PEGylated on two lysines with 5 kDa linear PEGs (mPEG-succinimidyl valerate, MW 5000) and studied in the absence and presence of preferentially excluded sucrose and preferentially bound guanine hydrochloride. Structural characterization by far- and near-UV circular dichroism spectroscopy was supplemented by investigation of protein thermal stability with the use of differential scanning calorimetry, far and near-UV circular dichroism and fluorescence spectroscopy. It was found that PEGylated lysozyme was stabilized by the preferentially excluded excipient and destabilized by the preferentially bound excipient in a similar manner as lysozyme. However, compared to lysozyme in all cases the melting transition was lower by up to a few degrees and the calorimetric melting enthalpy was decreased to half the value for PEGylated lysozyme. The ratio between calorimetric and van’t Hoff enthalpy suggests that our PEGylated lysozyme is a dimer.

Conclusion/Significance

The PEGylated model protein displayed similar stability responses to the addition of preferentially active excipients. This suggests that formulation principles using preferentially interacting excipients are similar for PEGylated and non-PEGylated proteins.