Osmolyte Effects on Monoclonal Antibody Stability and Concentration-Dependent Protein Interactions with Water and Common Osmolytes

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Do Ionic Liquids Exhibit the Required Characteristics to Dissolve, Extract, Stabilize, and Purify Proteins? Past-Present-Future Assessment

Proteins are highly labile molecules, thus requiring the presence of appropriate solvents and excipients in their liquid milieu to keep their stability and biological activity. In this field, ionic liquids (ILs) have gained momentum in the past years, with a relevant number of works reporting their successful use to dissolve, stabilize, extract, and purify proteins. Different approaches in protein-IL systems have been reported, namely, proteins dissolved in (i) neat ILs, (ii) ILs as co-solvents, (iii) ILs as adjuvants, (iv) ILs as surfactants, (v) ILs as phase-forming components of aqueous biphasic systems, and (vi) IL-polymer-protein/peptide conjugates. Herein, we critically analyze the works published to date and provide a comprehensive understanding of the IL-protein interactions affecting the stability, conformational alteration, unfolding, misfolding, and refolding of proteins while providing directions for future studies in view of imminent applications. Overall, it has been found that the stability or purification of proteins by ILs is bispecific and depends on the structure of both the IL and the protein. The most promising IL-protein systems are identified, which is valuable when foreseeing market applications of ILs, e.g., in "protein packaging" and "detergent applications". Future directions and other possibilities of IL-protein systems in light-harvesting and biotechnology/biomedical applications are discussed.

Impact of Glycosylation on Protein-Protein Self-Interactions of Monoclonal Antibodies

Protein self-interactions measured via second osmotic virial coefficients (B22) and dynamic light scattering interaction parameter values (kD) are often used as metrics for assessing the favorability of protein candidates and different formulations during monoclonal antibody (MAb) product development. Model predictions of B22 or kD typically do not account for glycans, though glycosylation can potentially impact experimental MAb self-interactions. To the best of our knowledge, the impact of MAb glycosylation on the experimentally measured B22 and kD values has not yet been reported. B22 and kD values of two fully deglycosylated MAbs and their native (i.e., fully glycosylated) counterparts were measured by light scattering over a range of pH and ionic strength conditions. Significant differences between B22 and kD of the native and deglycosylated forms were observed at a range of low to high ionic strengths used to modulate the effect of electrostatic contributions. Differences were most pronounced at low ionic strength, indicating that electrostatic interactions are a contributing factor. Though B22 and kD values were statistically equivalent at high ionic strengths where electrostatics were fully screened, we observed protein-dependent qualitative differences, which indicate that steric interactions may also play a role in the observed B22 and kD differences. A domain-level coarse-grained molecular model accounting for charge differences was considered to potentially provide additional insight but was not fully predictive of the behavior across all of the solution conditions investigated. This highlights that both the level of modeling and lack of inclusion of glycans may limit existing models in making quantitatively accurate predictions of self-interactions.

Computational Procedure for Predicting Excipient Effects on Protein-Protein Affinities

Protein-protein interactions lie at the center of many biological processes and are a challenge in formulating biological drugs, such as antibodies. A key to mitigating protein association is to use small-molecule additives, i.e., excipients that can weaken protein-protein interactions. Here, we develop a computationally efficient model for predicting the viscosity-reducing effect of different excipient molecules by combining atomic-resolution MD simulations, binding polynomials, and a thermodynamic perturbation theory. In a proof of principle, this method successfully ranks the order of four types of excipients known to reduce the viscosity of solutions of a particular monoclonal antibody. This approach appears useful for predicting the effects of excipients on protein association and phase separation, as well as the effects of buffers on protein solutions.

A computational procedure for predicting excipient effects on protein-protein affinities

Protein-protein interactions lie at the center of much biology and are a challenge in formulating biological drugs such as antibodies. A key to mitigating protein association is to use small molecule additives, i.e. excipients that can weaken protein-protein interactions. Here, we develop a computationally efficient model for predicting the viscosity-reducing effect of different excipient molecules by combining atomic-resolution MD simulations, binding polynomials and a thermodynamic perturbation theory. In a proof of principle, this method successfully rank orders four types of excipients known to reduce the viscosity of solutions of a particular monoclonal antibody. This approach appears useful for predicting effects of excipients on protein association and phase separation, as well as the effects of buffers on protein solutions.

Lot-to-Lot Variance in Immunoassays-Causes, Consequences, and Solutions

Immunoassays, which have gained popularity in clinical practice and modern biomedical research, play an increasingly important role in quantifying various analytes in biological samples. Despite their high sensitivity and specificity, as well as their ability to analyze multiple samples in a single run, immunoassays are plagued by the problem of lot-to-lot variance (LTLV). LTLV negatively affects assay accuracy, precision, and specificity, leading to considerable uncertainty in reported results. Therefore, maintaining consistency in technical performance over time presents a challenge in reproducing immunoassays. In this article, we share our two-decade-long experience and delve into the reasons for and locations of LTLV, as well as explore methods to mitigate its effects. Our investigation identifies potential contributing factors, including quality fluctuation in critical raw materials and deviations in manufacturing processes. These findings offer valuable insights to developers and researchers working with immunoassays, emphasizing the importance of considering lot-to-lot variance in assay development and application.

Two peak elution behavior of a monoclonal antibody in cation exchange chromatography as a screening tool for excipients

Aggregation of proteins is a critical quality attribute and a major concern during the purification of therapeutic proteins, like monoclonal antibodies. In-solution experiments applying different stress scenarios, e.g., mechanical, or physical stresses, can determine the overall conformational stability of the protein to enhance drug product shelf-life. Several groups have reported surface-induced unfolding and aggregation of monoclonal antibodies and their derivatives during cation exchange chromatography, which results in a two-peak elution behavior of the protein and its species. We have investigated universal influencing factors, like temperature and hold time, on this phenomenon. The formation of the second peak is a kinetic process, which is strongly influenced by temperature during the hold time. However, our main focus was the application of excipients and their influence on the two-peak elution behavior. We compared the on-column screening results with results obtained through a "traditional" in-solution screening using nanoDSF. Mostly, stabilizing excipients, like Sucrose, show their stabilizing abilities in both systems, but some discrepancies, e.g., using Arginine, between the two orthogonal techniques show the potential of the on-column screening system to lead to unexpected results, which would not necessarily be visible in in-solution experiments.

An open-source automated PEG precipitation assay to measure the relative solubility of proteins with low material requirement

The solubility of proteins correlates with a variety of their properties, including function, production yield, pharmacokinetics, and formulation at high concentrations. High solubility is therefore a key requirement for the development of protein-based reagents for applications in life sciences, biotechnology, diagnostics, and therapeutics. Accurate solubility measurements, however, remain challenging and resource intensive, which limits their throughput and hence their applicability at the early stages of development pipelines, when long-lists of candidates are typically available in minute amounts. Here, we present an automated method based on the titration of a crowding agent (polyethylene glycol, PEG) to quantitatively assess relative solubility of proteins using about 200 µg of purified material. Our results demonstrate that this method is accurate and economical in material requirement and costs of reagents, which makes it suitable for high-throughput screening. This approach is freely-shared and based on a low cost, open-source liquid-handling robot. We anticipate that this method will facilitate the assessment of the developability of proteins and make it substantially more accessible.

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.

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.

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.

Coarse-Grained Molecular Dynamics Simulations for Understanding the Impact of Short-Range Anisotropic Attractions on Structure and Viscosity of Concentrated Monoclonal Antibody Solutions

Understanding protein-protein interactions in concentrated therapeutic monoclonal antibody (mAb) solutions is desirable for improved drug discovery, processing, and administration. Here, we deduce both the net protein charge and the magnitude and geometry of short-ranged, anisotropic attractions of a mAb across multiple concentrations and cosolute conditions by comparing structure factors S(q) obtained from small-angle X-ray scattering experiments with those from molecular dynamics (MD) simulations. The simulations, which utilize coarse-grained 12-bead models exhibiting a uniform van der Waals attraction, uniform electrostatic repulsion, and short-range attractions between specific beads, are versatile enough to fit S(q) of a wide range of protein concentrations and ionic strength with the same charge on each bead and a single anisotropic short-range attraction strength. Cluster size distributions (CSDs) obtained from best fit simulations reveal that the experimental structure is consistent with small reversible oligomers in even low viscosity systems and help quantify the impact of these clusters on viscosity. The ability to systematically use experimental S(q) data together with MD simulations to discriminate between different possible protein-protein interactions, as well as to predict viscosities from protein CSDs, is beneficial for designing mAbs and developing formulation strategies that avoid high viscosities and aggregation at high concentration.

Isotonic concentrations of excipients control the dimerization rate of a therapeutic immunoglobulin G1 antibody during refrigerated storage based on their rank order of native-state interaction

Inert co-solutes, or excipients, are often included in protein biologic formulations to adjust the tonicity of liquid dosage forms intended for subcutaneous delivery. Despite the low concentration of their use, many of these excipients alter protein-protein interactions such as dimerization and aggregation rates of high concentration monoclonal antibody (mAb) therapeutics to varying extents during long-term refrigerated clinical storage, challenging the formulation scientist to make informed excipient selections at the earliest stages of development when protein supply and time are often limited. The objectives of this study were to better understand how isotonic concentrations of excipients influence the dimerization rates of a model mAb stored at refrigerated and room temperatures and explore protein sparing biophysical methods capable of predicting this dependence. Despite their prevalence of use in the biopharmaceutical industry, methods for assessing conformational stability such differential scanning calorimetry and isothermal equilibrium unfolding showed little predictive power and we highlight some of the assumptions and technical challenges of their use with mAbs. Conversely, measures of colloidal stability of the native-state such as preferential interaction coefficients measured by vapor pressure osmometry and solubility assessed by polyethylene-glycol induced precipitation correlated reasonably well with the mAb dimerization data and are most consistent with the excipients tested minimizing dimerization by interacting favorably with the residues comprising the protein-protein association interface.

Molecular Computations of Preferential Interaction Coefficients of IgG1 Monoclonal Antibodies with Sorbitol, Sucrose, and Trehalose and the Impact of These Excipients on Aggregation and Viscosity

Preferential interactions of formulation excipients govern their overall interactions with protein molecules, and molecular dynamics simulations allow for the examination of the interactions at the molecular level. We used molecular dynamics simulations to examine the interactions of sorbitol, sucrose, and trehalose with three different IgG1 antibodies to gain insight into how these excipients impact aggregation and viscosity. We found that sucrose and trehalose reduce aggregation more than sorbitol because of their larger size and their stronger interactions with high-spatial aggregation propensity residues compared to sorbitol. Two of the antibodies had high viscosity in sodium acetate buffer, and for these, we found that sucrose and trehalose tended to have opposite effects on viscosity. The data presented here provide further insight into the mechanisms of interactions of these three carbohydrate excipients with the antibody surface and thus their impact on excipient stabilization of antibody formulations.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Precipitation of complex antibody solutions: influence of contaminant composition and cell culture medium on the precipitation behavior

Preparative protein precipitation is known as a cost-efficient and easy-to-use alternative to chromatographic purification steps. This said, at the moment, there is no process for monoclonal antibodies (mAb) on the market, although especially polyethylene glycol-induced precipitation has shown great potential. One reason might be the highly complex behavior of each component of a crude feedstock during the precipitation process. For different investigated mAbs, significant variations in the host cell protein (HCP) reduction are observed. In contrast to the precipitation behavior of single components, the interactions and interplay in a complex feedstock are not fully understood yet. This work discusses the influence of contaminants on the precipitation behavior of two different mAbs, an IgG1, and an IgG2. By spiking the mAbs with mock solution, a complex feedstock could successfully be mimicked. Spiking contaminants influenced the yield and purity of the mAbs after the precipitation step, compared to the precipitation behavior of the single components. The mixture showed a decrease in the contaminant and mAb solubility. By re-buffering the mock solution prior to spiking, special salts, small molecules like amino acids, vitamins, or sugars could be depleted while larger ones like HCP or DNA were still present. Therefore, it was possible to distinguish the influence of small molecules and larger ones. Hence, mAb-macromolecular interaction could be identified as a possible reason for the observed higher precipitation propensity, while small molecules of the cell culture medium were identified as solubilisation factors during the precipitation process.

Cluster Formation and Entanglement in the Rheology of Antibody Solutions

Antibody solutions deviate from the dynamical and rheological response expected for globular proteins, especially as the volume fraction is increased. Experimental evidence shows that antibodies can reversibly bind to each other via F_ab and F_c domains and form larger structures (clusters) of several antibodies. Here, we present a microscopic equilibrium model to account for the distribution of cluster sizes. Antibody clusters are modeled as polymers that can grow via reversible bonds either between two F_ab domains or between F_ab and F_c domain. We propose that the dynamical and rheological behavior is determined by molecular entanglements of the clusters. This entanglement does not occur at low concentrations where antibody-antibody binding contributes to the viscosity by increasing the effective size of the particles. The model explains the observed shear-thinning behavior of antibody solutions.

Effect of additives on liquid droplet of protein-polyelectrolyte complex for high-concentration formulations

Liquid droplets of protein-polyelectrolyte complexes (PPCs) have been developed as a new candidate for stabilization and concentration of protein drugs. However, it remains unclear whether additives affect the precipitation and redissolution yields of PPCs. In the present study, we investigated the PPC formation of human immunoglobulin G (IgG) and poly-L-glutamic acid (polyE) in the presence of various additives that have diverse effects, such as protein stabilization. Alcohols, including ethanol, successfully increased the PPC precipitation yield to over 90%, and the PPCs formed were completely redissolved at physiological ionic strength. However, poly(ethylene glycol), sugars, and amino acids did not improve the precipitation and redissolution yields of PPCs over those observed when no additives were included. Circular dichroism spectrometry showed that the secondary structure of polyE as well as electrostatic interactions play important roles in increasing the PPC precipitation yield when ethanol is used as an additive. The maximum concentration of IgG reached 100 mg/ml with the use of ethanol, which was 15% higher efficiency of the protein yield after precipitation and redissolution than that in the absence of additives. Thus, the addition of a small amount of ethanol is effective for the concentration and stabilization of precipitated PPCs containing IgG formulations.

Taurine reduces blue light-induced retinal neuronal cell apoptosis in vitro

BACKGROUND

The massive uptake of organic compatible osmolytes is a self-protective response to multiple stressors.

OBJECTIVE

This study aimed to determine the protective effects of the osmolyte taurine against blue light-induced apoptosis in retinal neuronal cells in vitro.

METHODS

Real-time PCR was used to measure osmolyte transport. Radioimmunoassays were performed to measure osmolyte uptake. Cell Counting Kit-8 assays were conducted to measure cellular viability. Flow cytometry analysis was used to measure apoptosis.

RESULTS

Compared with normotonic stress, hypertonic stress-induced uptake of osmolytes, including betaine, myoinositol, and taurine, into the retinal neuronal cells. Blue light increased osmolyte transporter mRNA expression together with osmolyte uptake. Furthermore, taurine significantly suppressed blue light-induced retinal neuronal cell apoptosis.

CONCLUSION

The compatible osmolyte taurine may have an important role in cell resistance to blue light and cell survival.

Retracted: Molecular characterization of excipients' preferential interactions with therapeutic monoclonal antibodies

Retraction: Molecular characterization of excipients' preferential interactions with therapeutic monoclonal antibodies by Jehoon Kim, Mark R. H. Krebs and Bernhardt L. Trout The above article from the Journal of Pharmacy and Pharmacology, first published online on 4 August 2017 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the journal Editor-in-Chief, Professor David Jones, and John Wiley & Sons Ltd. The authors discovered that the analysis of simulations was faulty making the data incorrect. Reference Kim J et al. Molecular characterization of excipients' preferential interactions with therapeutic monoclonal antibodies. J Pharm Pharmacol 2017. https://doi.org/10.1111/jphp.12787.

Changing relations between proteins and osmolytes: a choice of nature

The stabilization and destabilization of the protein in the presence of any additive is mainly attributed to its preferential exclusion from protein surface and its preferential binding to the protein surface, respectively.

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.

Preferential interactions of trehalose, L-arginine.HCl and sodium chloride with therapeutically relevant IgG1 monoclonal antibodies

Preferential interactions of weakly interacting formulation excipients govern their effect on the equilibrium and kinetics of several reactions of protein molecules in solution. Using vapor pressure osmometry, we characterized the preferential interactions of commonly used excipients trehalose, L-arginine.HCl and NaCl with three therapeutically-relevant, IgG1 monoclonal antibodies that have similar size and shape, but differ in their surface hydrophobicity and net charge. We further characterized the effect of these excipients on the reversible self-association, aggregation and viscosity behavior of these antibody molecules. We report that trehalose, L-arginine.HCl and NaCl are all excluded from the surface of the three IgG1 monoclonal antibodies, and that the exclusion behavior is linearly related to the excipient molality in the case of trehalose and NaCl, whereas a non-linear behavior is observed for L-arginine.HCl. Interestingly, we find that the magnitude of trehalose exclusion depends upon the nature of the protein surface. Such behavior is not observed in case of NaCl and L-arginine.HCl as they are excluded to the same extent from the surface of all three antibody molecules tested in this study. Analysis of data presented in this study provides further insight into the mechanisms governing excipient-mediated stabilization of mAb formulations.

Cosolutes, Crowding, and Protein Folding Kinetics

Long accepted as the most important interaction, recent work shows that steric repulsions alone cannot explain the effects of macromolecular cosolutes on the equilibrium thermodynamics of protein stability. Instead, chemical interactions have been shown to modulate, and even dominate, crowding-induced steric repulsions. Here, we use 19F NMR to examine the effects of small and large cosolutes on the kinetics of protein folding and unfolding using the metastable 7 kDa N-terminal SH3 domain of the Drosophila signaling protein drk (SH3), which folds by a two-state mechanism. The small cosolutes consist of trimethylamine N-oxide and sucrose, which increase equilibrium protein stability, and urea, which destabilizes proteins. The macromolecules comprise the stabilizing sucrose polymer, Ficoll, and the destabilizing globular protein, lysozyme. We assessed the effects of these cosolutes on the differences in free energy between the folded state and the transition state and between the unfolded ensemble and the transition state. We then examined the temperature dependence to assess changes in activation enthalpy and entropy. The enthalpically mediated effects are more complicated than suggested by equilibrium measurements. We also observed enthalpic effects with the supposedly inert sucrose polymer, Ficoll, that arise from its macromolecular nature. Assessment of activation entropies shows important contributions from solvent and cosolute, in addition to the configurational entropy of the protein that, again, cannot be gleaned from equilibrium data. Comparing the effects of Ficoll to those of the more physiologically relevant cosolute lysozyme reveals that synthetic polymers are not appropriate models for understanding the kinetics of protein folding in cells.

Recombinant production of Aspergillus Flavus uricase and investigation of its thermal stability in the presence of raffinose and lactose

Aspergillus flavus uricase (Rasburicase) with a molecular mass of 135 kDa is currently used for the treatment of gout and hyperuricemia occurring in tumor lysis syndrome. To characterize the effects of raffinose and lactose osmolytes on the uricase structure, its coding sequence was cloned, expressed in E. coli BL21, and purified by Ni-NTA agarose affinity chromatography. Thermal inactivation studies at 40 °C showed that nearly 15% of UOX activity was preserved, while the presence of raffinose and lactose reduced its activity to 35 and 45% of its original activity, respectively. Investigation of UOX thermal stability at 40 °C in the course of time showed that the enzyme relatively lost almost 60% of its original activity after 40 min, whereas more than 50% of UOX activity is preserved in the presence of lactose. Estimation of thermal inactivation rate constant, k _in, showed that the UOX k _in and UOX k _in in the presence of raffinose was unchanged (0.018 min^-1), whereas for the presence of lactose, it was 0.015 min^-1. Half-life and T _m analysis showed that UOX half-life is almost 38 min and addition of raffinose did not change the half-life, whereas the presence of lactose had remarkable impact on UOX half-life (46 min). The presence of raffinose increased UOX T _m to a lesser extent, whereas lactose notably enhanced the T _m from 27 to 37 °C. Overall, our findings show that lactose has protective effects on UOX stability, while for raffinose, it is relatively compromised.

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.