Suppression of protein interactions by arginine: a proposed mechanism of the arginine effects

Impact of arginine addition on protein concentration via ultrafiltration

In this study, we examined the effects of arginine (L-ArgHCl) on ultrafiltration performance, a process with practical significance for not only research but also pharmaceutical applications. Specifically, we assessed the yield and filtration rate of ultrafiltration using rabbit and goat polyclonal antibodies (neutral to basic isoelectric points) as well as model proteins, BSA (acidic) and lysozyme (basic). When a 1 mg/mL protein solution was concentrated approximately 10-fold using a standard commercially available centrifugal ultrafiltration device, the addition of L-ArgHCl significantly improved yield at near-neutral buffer pH. The observed order of improvement was: 20 mM L-ArgHCl >100 mM L-ArgHCl ≈0.5 M NaCl > no addition. A similar trend was observed with BSA, whereas lysozyme achieved slightly higher yields at 100 mM L-ArgHCl. In a 40-fold concentration of rabbit polyclonal antibody from 1 mg/mL, 20 mM L-ArgHCl enhanced yield at pH 6 and 7, but had minimal or no effect at pH 7.5. Notably, at pH 8, high yields were achieved without arginine. L-ArgHCl also accelerated the concentration rate at all pH levels, with greater enhancements observed at higher arginine concentrations. These findings suggest that L-ArgHCl mitigates protein precipitation and solubility loss by reducing protein-protein interactions and nonspecific binding to the ultrafiltration membrane. At pH 8, the increased surface charge of the antibody reduced hydrophobicity, further improving solubility. In summary, the addition of L-ArgHCl, particularly near pH 7, effectively enhanced ultrafiltration performance. This provides a practical strategy for improving protein concentration processes.

Impact of protein adsorption during biopharmaceutical manufacture & storage

Protein therapeutics contact multiple interfaces during formulation, filtration, fill-finish, and storage processes. Interactions at these interfaces can compromise the conformational and colloidal stability of therapeutic proteins through surface adsorption, potentially leading to aggregation and particle formation. Surface-induced conformational changes in protein higher-order structures, influenced by interfacial hydrophobicity and charge, are key drivers of these effects. The resulting loss of active protein and increased aggregation risk pose significant challenges to the efficacy and safety of the final biotherapeutic product. Thus, it is imperative to develop strategies that minimize protein-surface interactions that may compromise the protein's conformational and colloidal stability during manufacture and storage. This review focuses on current research related to the adsorption behaviour of biotherapeutics at interfaces encountered during fill-finish and storage. Furthermore, the review introduces the factors influencing protein adsorption and interfacial stability and current methodologies and advancements in mitigating interfacial adsorption, emphasizing rational formulation design strategies.

Protein identification using Cryo-EM and artificial intelligence guides improved sample purification

Protein purification is essential in protein biochemistry, structural biology, and protein design, enabling the determination of protein structures, the study of biological mechanisms, and the characterization of both natural and de novo designed proteins. However, standard purification strategies often encounter challenges, such as unintended co-purification of contaminants alongside the target protein. This issue is particularly problematic for self-assembling protein nanomaterials, where unexpected geometries may reflect novel assembly states, cross-contamination, or native proteins originating from the expression host. Here, we used an automated structure-to-sequence pipeline to first identify an unknown co-purifying protein found in several purified designed protein samples. By integrating cryo-electron microscopy (Cryo-EM), ModelAngelo's sequence-agnostic model-building, and Protein BLAST, we identified the contaminant as dihydrolipoamide succinyltransferase (DLST). This identification was validated through comparisons with DLST structures in the Protein Data Bank, AlphaFold 3 predictions based on the DLST sequence from our E. coli expression vector, and traditional biochemical methods. The identification informed subsequent modifications to our purification protocol, which successfully excluded DLST from future preparations. To explore the potential broader utility of this approach, we benchmarked four computational methods for DLST identification across varying resolution ranges. This study demonstrates the successful application of a structure-to-sequence protein identification workflow, integrating Cryo-EM, ModelAngelo, Protein BLAST, and AlphaFold 3 predictions, to identify and ultimately help guide the removal of DLST from sample purification efforts. It highlights the potential of combining Cryo-EM with AI-driven tools for accurate protein identification and addressing purification challenges across diverse contexts in protein science.

Unraveling the unique amyloid-like aggregation behavior of the tumor suppressor p53 mutants in human cancers

Missense mutations in the tumor suppressor p53 significantly disrupt its native structure and functions, playing a pivotal role in human cancer pathogenesis. Oncogenic mutant p53 (mutp53) not only loses its tumor-suppressive capabilities but also acquires oncogenic functions, driving cancer progression, metastasis, and chemoresistance. Despite extensive research on mutp53, the role of missense mutations in triggering amyloid-like aggregation of p53 remains an underexplored and fascinating area of study. To date, over 50 proteins are known to form amyloid-like aggregates due to abnormal folding, resulting in insoluble protein fibrils that contribute to various protein misfolding diseases, including cancer. However, the precise mechanisms by which aggregated proteins induce cancer remain inadequately understood. Notably, certain p53 mutations promote its aggregation, which has emerged as a critical factor in protein aggregation-induced oncogenesis. This review delves into the mechanisms underpinning mutp53 aggregation, emphasizing unique properties such as coaggregation, bio-isolation, prion-like cell-to-cell transmission, and chemoresistance promotion. Leveraging diverse in-silico, biophysical, and biochemical approaches, we comprehensively analyzed the aggregating potential of 26 mutp53 variants among 1297 missense mutations identified in human cancers. These findings shed light on the multifaceted roles of mutp53 aggregates in oncogenesis and tumor progression. Lastly, we present an integrative exploration of emerging therapeutic strategies designed to disaggregate mutp53 aggregates, offering promising directions for targeted cancer therapy. By addressing this enigmatic aspect of mutp53 biology, our review advances the understanding of protein aggregation in cancer and identifies avenues for innovative therapeutic interventions.

Influence of physicochemical conditions on liquid-liquid phase separation and stability of immunoglobulin Y for storage and application

Liquid-liquid phase separation (LLPS) is a biological process and can lead to the formation of irreversible aggregates of functional proteins upon storage and administration, making it essential to predict and mitigate this phenomenon. Immunoglobulin Y (IgY), a unique class of antibody derived from egg yolk has broad applications in disease diagnosis, prophylaxis, and treatment. In this study, we observed the formation of droplet-shaped condensates of IgY under crowding conditions with polyethylene glycol 8000 (PEG 8000). To assess the relative contribution of different IgY domains to LLPS, we prepared the fragment antigen binding (Fab), fragment crystallizable (Fc) 3-4, and Escherichia coli-expressed IgY-Fc 2-4 domain. After PEG 8000 addition, the Fab fragments more propensity to aggregate, while Fc 3-4 and E. coli-expressed Fc underwent LLPS. Furthermore, we found that LLPS of IgY is influenced by electrostatic interactions. Recognizing the negative effects of LLPS on antibody efficacy, our study showed that the addition of arginine and lysine at low concentrations could prevent PEG-induced LLPS, enhancing IgY stability. These findings provide valuable insights into the optimization of IgY antibody applications and storage conditions, advancing our understanding of antibody stability in solution and facilitating the development of strategies to protect antibodies from aggregation.

Flipping out: role of arginine in hydrophobic interactions and biological formulation design

Arginine has been a mainstay in biological formulation development for decades. To date, the way arginine modulates protein stability has been widely studied and debated. Here, we employed a hydrophobic polymer to decouple hydrophobic effects from other interactions relevant to protein folding. While existing hypotheses for the effects of arginine can generally be categorized as either direct or indirect, our results indicate that direct and indirect mechanisms of arginine co-exist and oppose each other. At low concentrations, arginine was observed to stabilize hydrophobic polymer folding via a sidechain-dominated direct mechanism, while at high concentrations, arginine stabilized polymer folding via a backbone-dominated indirect mechanism. Upon introducing partially charged polymer sites, arginine destabilized polymer folding. Further, we found arginine-induced destabilization of a model virus similar to direct-mechanism destabilization of the charged polymer and concentration-dependent stabilization of a model protein similar to the indirect mechanism of hydrophobic polymer stabilization. These findings highlight the modular nature of the widely used additive arginine, with relevance in the information-driven design of stable biological formulations.

Additive effects of the new viscosity-reducing and stabilizing excipients for monoclonal antibody formulation

The subcutaneous administration of biopharmaceuticals is advantageous over intravenous administration, particularly with regard to improved patient compliance. However, in highly concentrated protein formulations lower viscosity of the formulation and stability of the protein is difficult to achieve. One approach involves using the viscosity-reducing excipients to diminish the interactions between protein molecules. In this context, the main objective of the study was to develop an optimal formulation for a model monoclonal antibody (mAb) and to evaluate new test compounds as viscosity-reducing agents. The test compounds were investigated both individually at increasing concentrations up to 200 mM and in combinations for their viscosity-reducing effect. Our results showed that all individual test compounds reduced the viscosity of the mAb formulation by more than 30 %, with reduction achieved by the six test compounds exceeding that achieved by proline (Pro). A reduction in the viscosity of the formulation below the 20 mPas threshold was achieved either by combining two test compounds or by increasing the concentration of a single compound above 25 mM. An accelerated stability study showed similar stabilization effects regardless of whether the test compounds were used alone or in combination. The percentage of aggregates was below 5 % in most formulations. These viscosity-reducing and stabilization effects corresponded to the dynamic light scattering results, which indicated that the test compounds reduced the attractive forces between the mAb molecules.

Predictive mechanistic model for separation of monoclonal antibody, fab fragment, and aggregate species on multimodal chromatography

The specific selectivities offered by multimodal ligands drive the increased application of multimodal chromatography in the purification of complex new "multispecific" antibodies, which requires improved understanding of the protein-multimodal ligand interaction mechanism. In the present study, a mechanistic model is developed to predict monoclonal antibody (mAb1)-Fab fragment (Fab) and heterogeneous aggregates separation on Capto™ MMC ImpRes multimodal resin based on the general rate model coupled with the proposed preferential interaction (PI) analysis-based Langmuir non-linear binding model. The model input value of binding parameters is obtained from Perkin et al. developed PI model, fit to the characteristic 'U'-shaped curve for isocratic retention factors of mAb1, Fab, and aggregates as a function of NaCl salt concentrations. The model successfully simulates mAb1 and Fab elution peaks, whereas in the absence of deconvoluted peaks of heterogeneous aggregates, aggregates are modeled as a single species, giving satisfactory prediction of elution peak position, describing the average of the multiple (majority as double peaks) aggregate elution peaks. The physical significance of model estimated binding parameters is obtained from model estimated total number of released counter salt ions and water molecules for each species during binding, found to be consistent with their isocratic retention data. The underlying mechanism of double peak elution of aggregates during linear gradient elution was investigated based on mechanistic model estimated equilibrium constant. The proposed predictive mechanistic model was successfully validated by predicting mAb1, Fab, and aggregates elution peaks for the multimodal column operated in hydrophobic interaction mode and can be successfully implemented for process development.

Advances in Reducing Salt Content in Processed Meats with Basic Amino Acids

Basic amino acids have emerged as a pivotal area of research in efforts to decrease the sodium content in meat products, primarily due to their ability to enhance flavor, improve taste, and effectively replace sodium salts. This review synthesizes current strategies for sodium reduction in meat products and offers an overview of previous studies examining the role of basic amino acids in such applications, including their impact on sensory attributes and structural alterations. Furthermore, the implications of these strategies on product quality are examined, addressing aspects such as protein hydrolysis, oxidation, color, and textural changes, as well as potential underlying mechanisms. Additionally, future challenges and trends in the utilization of basic amino acids in processed meats are explored. Overall, basic amino acids exhibit significant potential as sodium salt substitutes, particularly at low NaCl concentrations. Their combinations with chloride salts, yeast extracts, and other salts have been explored as alternative sodium reduction strategies. However, challenges remain in their application to meat products, including high production costs, consumer acceptance, and stability during large-scale production. Future research should focus on optimizing the use of basic amino acids, enhancing their economic feasibility, and addressing technical hurdles.

Strategy to mitigate aggregation during Protein A chromatography and low pH virus inactivation for a nivolumab biosimilar candidate

Protein A chromatography represents the most prevalent methodology for the capture of monoclonal antibodies. The use of a low pH elution buffer from Protein A has been observed to contribute to product aggregation, particularly in the case of IgG4 antibodies, such as nivolumab. This paper presents a well-defined strategy for addressing this issue. Initial experiments were conducted at scale-down Protein A affinity chromatography to evaluate the use of glycine-HCL and sodium citrate as elution buffers at pH values of 3.25, 3.5, and 3.75. Subsequently, a scale-down screening was conducted to assess the efficacy of various additives in Protein A elution. These included 10 % (w/v) mannitol, 50 mM histidine, 50 mM sucrose, 10 % (v/v) sorbitol, 50 mM arginine, 50 mM trehalose, 0.02 % (v/v) polysorbate 80, 1.5 M urea, and 1 M MgCl2. The three most stabilizing additives were evaluated at the laboratory scale, and the one that demonstrated the greatest ability to maintain the minimum high molecular weight aggregate over time was selected. Lastly, the selected additive was subjected to testing at elevated IgG concentrations during purification. Nivolumab exhibits a markedly pH-dependent propensity for aggregation, and the relative efficacy of glycine-HCL and sodium citrate in mitigating anti-PD1 aggregation within the pH range of 3.25 to 3.75 is subject to variation. The use of buffer 100 mM sodium citrate, pH 3.5 was found to be beneficial. All additives evaluated contribute to reducing nivolumab aggregation, albeit in different ways and to varying degrees of effectiveness. Elution buffer with mannitol, polysorbate 80, or MgCl₂ resulted in a monomer control ratio of approximately twice that observed in the absence of additives. However, the stabilizing role of mannitol was confirmed to be particularly significant, as the ratio of aggregation formed at a low pH was reduced to ≤ 2 % from 15 % in all evaluated scales and at different protein concentrations, while maintaining high biological activity.

Inhibitory effect of L-arginine on the oxidative aggregation behavior of myofibrillar proteins in the Antarctic krill (Euphausia superba): pH and antioxidation

In this study, the effect of L-arginine (L-Arg) on the oxidative aggregation of myofibrillar proteins (MPs) in Antarctic krill was evaluated. The results showed that the oxidized aggregation of MPs was significantly inhibited after the addition of 20 mM L-Arg compared to the oxidized group, the solubility of MPs significantly increased by 25.74 %, the turbidity reduced from 0.56 to 0.18. These effects were primarily attributed to the addition of L-Arg, which prevented the unfolding of the spatial structure of MPs after oxidation, inhibited the formation of disulfide bonds and dityrosine, and improved the stability of MPs structure. Analysis of carbonyl content and hydroxyl radical (•OH) inhibitory capacity showed that carbonyl formation and hydroxyl radicals were effectively reduced by the pH and guanidinium group of L-Arg. The pH of L-Arg exhibited a significantly higher effect than the guanidinium group in inhibiting the oxidative aggregation of MPs.

A multifaceted approach to understanding protein-buffer interactions in biopharmaceuticals

The excipient selection process plays a crucial role in biopharmaceutical formulation development to ensure the long-term stability of the drug product. Though there are numerous options approved by regulatory authorities, only a subset is commonly utilized. Previous research has proposed various stabilization mechanisms, including protein-excipient interactions. However, identifying these interactions remains challenging due to their weak and transient nature. In this study, we present a comprehensive approach to identify such interactions. Using the 1HT2 CPMG (Carr-Purcel-Meiboom-Gill) filter experiment we identified interactions of rituximab with certain buffers and amino acids, shedding light on its Fc fragment instability that manifested during the enzymatic cleavage of the antibody. Moreover, chemometric analyses of 2D NMR fingerprints revealed interactions of selected excipients with antibody fragments. Furthermore, molecular dynamics simulations revealed potential interacting hotspots without NMR spectra assignment. Our results highlight the importance of an orthogonal methods approach to uncovering these critical interactions, advancing our understanding of excipient stabilization mechanisms and rational formulation design in biopharmaceutics.

Arginine: A potential prophylactic supplement for transthyretin amyloidosis

Transthyretin (TTR) is an amyloidogenic protein associated with TTR amyloidosis (ATTR). Dissociation of TTR tetramers into TTR monomers causes TTR misfolding, resulting in amyloid fibril formation and triggering the onset of ATTR. Low-molecular-weight tetrameric TTR stabilizers are potential therapeutic agents to delay ATTR progression. However, the currently available drugs are expensive and cannot be used for prophylaxis. Therefore, in this study, we aimed to identify a prophylactic supplement that suppresses TTR amyloid formation. We investigated whether arginine, an amyloidogenic protein aggregation inhibitor, stabilizes tetrameric TTR, thereby preventing amyloid fibril formation. Immunoblotting showed that arginine mixed with wild-type TTR (TTRwt), amyloidogenic TTR Val30Met (ATTR V30M), and human serum samples reduced the amount of monomeric TTR but increased the tetramer/monomer ratio of TTR compared to those in the samples without arginine. Additionally, oral administration of arginine (5000 mg for 5 days) to healthy volunteers effectively increased the tetramer/monomer ratio of TTR in the serum. Thioflavin T test, a quantitative analysis method for amyloid fibril formation, showed that amyloid fibril formation was significantly suppressed with arginine compared to that without arginine. As arginine is a common supplement and non-toxic amino acid, it can be used as a promising prophylactic supplement to suppress amyloid fibril formation in ATTR.

Synergistic effect of cyclodextrins and electrolytes at high concentrations on protein aggregation inhibition

The stabilization of protein therapeutics against aggregation is crucial for maintaining their efficacy and safety. This study investigated the synergistic effects of cyclodextrins (CDs) and electrolytes at high concentrations on the stabilization of immunoglobulin G (IgG), insulin, and adeno-associated virus (AAV) vectors. The effects of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) combined with various electrolytes were evaluated using human plasma-derived IgG as a model protein. The HP-β-CD and L(+)-arginine hydrochloride combination synergistically increased the onset temperature of protein aggregation and inhibited the formation of soluble and insoluble aggregates during long-term storage. Notably, this synergistic effect was not observed when sucrose was used instead of HP-β-CD. Similar synergistic effects were observed with insulin and AAV vectors. The findings suggest that the stabilization mechanism could potentially involve enhanced interactions between HP-β-CD and IgG, preventing protein-protein interactions. However, the combination did not synergistically improve the solubility of free aromatic amino acids, including tyrosine and tryptophan. This study highlights the potential of using the combination of CDs and electrolytes as a promising formulation strategy for stabilizing complex protein therapeutics. Further studies are needed to elucidate the underlying mechanisms and generalize the approach to other proteins with varying physicochemical properties.

Respiratory delivered vaccines: Current status and perspectives in rational formulation design

The respiratory tract is susceptible to various infections and can be affected by many serious diseases. Vaccination is one of the most promising ways that prevent infectious diseases and treatment of some diseases such as malignancy. Direct delivery of vaccines to the respiratory tract could mimic the natural process of infection and shorten the delivery path, therefore unique mucosal immunity at the first line might be induced and the efficiency of delivery can be high. Despite considerable attempts at the development of respiratory vaccines, the rational formulation design still warrants attention, i.e., how the formulation composition, particle properties, formulation type (liquid or solid), and devices would influence the immune outcome. This article reviews the recent advances in the formulation design and development of respiratory vaccines. The focus is on the state of the art of delivering antigenic compounds through the respiratory tract, overcoming the pulmonary bio-barriers, enhancing delivery efficiencies of respiratory vaccines as well as maintaining the stability of vaccines during storage and use. The choice of devices and the influence of deposition sites on vaccine efficiencies were also reviewed.

Insulin Stabilization Designs for Enhanced Therapeutic Efficacy and Accessibility

Insulin has remained indispensable in the treatment of diabetes since it was first discovered in 1921. Unlike small molecular drugs, insulin and other protein drugs are prone to degradation when exposed to elevated temperatures, mechanical agitation during transportation, and prolonged storage periods. Therefore, strict cold-chain management is crucial for the insulin supply, requiring significant resources, which can limit the access to insulin, particularly in low-income areas. Moreover, although insulin formulations have advanced tremendously in the last century, insulin treatment still imposes a challenging regimen and provides suboptimal outcomes for the majority of patients. There is an increasing focus on pursuing improved pharmacology, specifically on safer, more user-friendly insulin therapies that minimize the self-management burden. These challenges underscore the need for developing novel insulin formulations with improved stability that are compatible with advanced insulin therapy. Insulin stabilization can be achieved through either chemical modification of insulin or formulation component design. Inspired by insulin-like peptides from invertebrates, we have developed novel stable insulin analogs based on a fundamental understanding of the insulin receptor engagement for insulin bioactivity. We created a novel four-disulfide insulin analog with high aggregation stability and potency by introducing a fourth disulfide bond between a C-terminal extended insulin A-chain and residues near the C-terminus of the B-chain. In an effort to stabilize insulin in its monomeric state to develop ultrafast-acting insulin with rapid absorption upon injection, we have developed a series of structurally miniaturized yet fully active insulin analogs that do not form dimers due to the lack of the canonical B-chain C-terminal octapeptide. Additionally, our study provided strategies for expanding the scope of cucurbit[7]uril (CB[7])-assisted insulin stabilization by engineering safe and biodegradable CB[7]-zwitterionic polypeptide excipients. We also explored insulin N-terminal substitution methods to achieve pH-dependent insulin stabilization without prolonging the duration of action. This Account describes our exploration of engineering stable insulin analogs and formulation design strategies for stabilizing insulin in aqueous solutions. Beyond conventional stabilization strategies for insulin injections, the unmet challenges and recent innovations in insulin stabilization are discussed, addressing the growing demand for alternative, less invasive routes of insulin administration. Additionally, we aim to provide a thorough overview of insulin stabilization from the perspective of commercially available insulin drugs and common pharmaceutical engineering practices in the industry. We also highlight unresolved insulin stabilization challenges and ongoing research strategies. We anticipate that further emphasis on collective efforts of protein engineering, pharmaceutical formulation design, and drug delivery will inform the development of stable and advanced insulin therapy.

Mitigation Strategies against Antibody Aggregation Induced by Oleic Acid in Liquid Formulations

Polysorbates 20 and 80 (PS20 and PS80) are commonly used in the formulations of biologics to protect against interfacial stresses. However, these surfactants can degrade over time, releasing free fatty acids, which assemble into solid particles or liquid droplets. Here, we apply a droplet microfluidic platform to analyze the interactions between antibodies and oleic acid, the primary free fatty acid resulting from the hydrolysis of PS80. We show that antibodies adsorb within seconds to the polar oleic acid-water interface, forming a viscoelastic protein layer that leads to particle formation upon mechanical rupture. By testing two different monoclonal antibodies of pharmaceutical origin, we show that the propensity to form a rigid viscoelastic layer is protein-specific. We further demonstrate that intact PS80 is effective in preventing antibody adsorption at the oleic acid-water interface only at low antibody concentrations and low pH, where oleic acid is fully protonated. Importantly, introduction of the amino acid l-arginine prevents the formation of the interfacial layer and protein particles even at high antibody concentrations (180 mg mL-1). Overall, our findings indicate that oleic acid droplets in antibody formulations can lead to the formation of protein particles via an interface-mediated mechanism. Depending on the conditions, intact PS80 alone might not be sufficient to protect against antibody aggregation. Additional mitigation strategies include the optimization of protein physicochemical properties, pH, and the addition of arginine.

Effectiveness of Lyoprotectants in Protein Stabilization During Lyophilization

Background: Proteins are commonly used in the healthcare industry to treat various health conditions, and most proteins are sensitive to physical and chemical changes. Lyophilization, also known as freeze-drying, involves sublimating water in the form of ice from a substance at low pressure, forming a freeze-dried powder that increases its shelf life. Extreme pressure and varying temperatures in the freeze-drying process may damage the protein's structural integrity. Lyoprotectants are commonly used to protect protein conformations. It is important to choose a suitable lyoprotectant to ensure optimal effectiveness. Method: Twenty articles screened from Scopus, Web of Science, and PubMed were included in this review that discussed potential lyoprotectants and their effectiveness with different protein models. Results: Lyoprotectants were categorized into sugars, polyols, surfactants, and amino acids. Lyoprotectants can exhibit significant protective effects towards proteins, either singularly or in combination with another lyoprotectant. They exert various interactions with the protein to stabilize it, such as hydrogen bonding, hydrophobic interactions, electrostatic interactions, and osmoprotection. Conclusions: This review concludes that disaccharides are the most effective lyoprotectants, while other groups of lyoprotectants are best used in combination with other lyoprotectants.

On the role of excipients in biopharmaceuticals manufacture: Modelling-guided formulation identifies the protective effect of arginine hydrochloride excipient on spray-dried Olipudase alfa recombinant protein

Biopharmaceuticals are labile biomolecules that must be safeguarded to ensure the safety, quality, and efficacy of the product. Batch freeze-drying is an established means of manufacturing solid biopharmaceuticals but alternative technologies such as spray-drying may be more suitable for continuous manufacturing of inhalable biopharmaceuticals. Here we assessed the feasibility of spray-drying Olipudase alfa, a novel parenteral therapeutic enzyme, by evaluating some of its critical quality attributes (CQAs) in a range of excipients, namely, trehalose, arginine (Arg), and arginine hydrochloride (Arg-HCl) in the sucrose/methionine base formulation. The Arg-HCl excipient produced the best gain in CQAs of spray-dried Olipudase with a 63% reduction in reconstitution time and 83% reduction in the optical density of the solution. Molecular dynamics simulations revealed the atomic-scale mechanism of the protein-excipient interactions, substantiating the experimental results. The Arg-HCl effect was explained by the calculated thermal stability and structural order of the protein wherein Arg-HCl acted as a crowding agent to suppress protein aggregation and promote stabilization of Olipudase post-spray-drying. Therefore, by rational selection of appropriate excipients, our experimental and modelling dataset confirms spray-drying is a promising technology for the manufacture of Olipudase and demonstrates the potential to accelerate development of continuous manufacturing of parenteral biopharmaceuticals.

A Novel Size Exclusion Chromatography Method for the Analysis of Monoclonal Antibodies and Antibody-drug Conjugates by Using Sodium Iodide in the Mobile Phase

PURPOSES

Size exclusion chromatography (SEC) is widely used to characterize molecular size variants of antibody drugs. However, SEC analysis is hindered by secondary interactions (or nonspecific interactions) between proteins and stationary phase packing, which result in poor column efficiency. Previous studies have reported that chaotropic salt can inhibit these interactions, but the corresponding applications of this aspect are relatively rare. Therefore, this study introduces a novel approach using sodium iodide (NaI) as a mobile-phase component in SEC and investigates the influence of the mobile-phase composition on secondary interactions.

METHODS

SEC analysis was performed on one antibody-drug conjugate and four monoclonal antibodies (mAbs) using three different mobile-phase systems (i.e., sodium chloride/L-arginine hydrochloride/NaI mobile phases system) to compare the column efficiency. Subsequently, mAb-1 was used as a model to investigate the effects of these factors on secondary interactions by adjusting the ionic strength (salt concentration) and pH of the NaI mobile-phase system.

RESULTS

NaI exhibits superior column efficiency performance in the SEC analysis of most products. The ionic strength will affect nonideal electrostatic and hydrophobic interaction. An appropriate ionic strength can inhibit electrostatic interactions, while an excessive ionic strength increases hydrophobic interactions. pH primarily influences electrostatic interactions. Determining the appropriate pH necessitates consideration of the isoelectric point of the protein and the pH tolerance of the column.

CONCLUSIONS

In SEC analysis, using NaI as the salt component in the mobile phase reduces secondary interactions and improves column efficiency. This approach is advantageous for samples with intense secondary interactions and is a suitable alternative.

The contrasting roles of co-solvents in protein formulations and food products

Protein aggregation is a major hurdle in developing biopharmaceuticals, in particular protein formulation area, but plays a pivotal role in food products. Co-solvents are used to suppress protein aggregation in pharmaceutical proteins. On the contrary, aggregation is encouraged in the process of food product making. Thus, it is expected that co-solvents play a contrasting role in biopharmaceutical formulation and food products. Here, we show several examples that utilize co-solvents, e.g., salting-out salts, sugars, polyols and divalent cations in promoting protein-protein interactions. The mechanisms of co-solvent effects on protein aggregation and solubility have been studied on aqueous protein solution and applied to develop pharmaceutical formulation based on the acquired scientific knowledge. On the contrary, co-solvents have been used in food industries based on empirical basis. Here, we will review the mechanisms of co-solvent effects on protein-protein interactions that can be applied to both pharmaceutical and food industries and hope to convey knowledge acquired through research on co-solvent interactions in aqueous protein solution and formulation to those involved in food science and provide those involved in protein solution research with the observations on aggregation behavior of food proteins.

Does arginine aggregate formation in aqueous solutions follow a two-step mechanism?

The formation of aggregates was studied in arginine aqueous solutions using light scattering. The main driving force for aggregate formation is hydrogen bonding between the arginine (Arg) amino acids, which is partially verified using density functional theory calculations. The measurement of energy loss during this process, coupled with Cryo-EM morphology data, indicates that these aggregates are in the solid state. The aggregation occurs in two steps, with a liquid intermediate stage. The investigation of the effect of pH and solute concentration on aggregate formation for other amino acid aqueous solutions verifies that aggregate formation is amino-acid specific, while small-sized clusters formed by weak interactions lead to large-sized aggregation. The water structure around amino acid molecules sheds light on the prediction of their aggregate formation. Homochirality is observed in the aggregates; its existence sheds light on the origin of protein homochirality.

Removal of empty capsids from high-dose adeno-associated virus 9 gene therapies

Recombinant adeno-associated virus, serotype 9 (rAAV9) has shown promise as a gene therapy vector for muscle and central nervous diseases. High-dose requirements of these therapies present critical safety considerations and biomanufacturing challenges. Notably, the reduction of empty capsids (ECs), which lack therapeutic transgene, from rAAV9 products is critical to maximize efficacy. Removal of rAAV ECs from full capsids is a major downstream challenge because of their highly similar biophysical characteristics. Ultracentrifugation (UC) reduces ECs but is laborious and difficult to scale. In this paper, to replace a poorly scalable UC process, we developed an anion exchange (AEX) chromatography for rAAV9 EC reduction from full capsids. AEX load preparation by dilution incurred major product loss. The addition of histidine and surfactants to dilution buffers increased yield and reduced aggregation. Elution salts were screened and sodium acetate was found to maximize yield and EC reduction. The most promising load dilution buffer and elution salt were used in combination to form an optimized AEX method. The process reduced ECs three-fold, demonstrated robustness to a broad range of EC load challenges, and was scaled for large-scale manufacture. Compared to UC, the AEX method simplified scale-up, reduced ECs to comparable levels (20%), afforded similar purity and product quality, and increased yield by 14%.

Exploring the Potential of Arginine to Increase Coelenterazine-Renilla Luciferase Affinity and Enzyme Stability: Kinetic and Molecular Dynamics Studies

Renilla luciferase catalyzes the oxidation of coelenterazine to coelenteramide and results in the emission of a photon of light. Although Renilla luciferase has various applications in biotechnology, its low thermal stability limits the development of its applications. Arginine is a well-known stabilizing amino acid that plays a key role in protein stabilization against inactivation. However, its impact on enzyme properties is unpredictable. This study investigates the impact of arginine on the kinetics and thermal stability of Renilla luciferase. The enzyme's performance was significantly enhanced in the presence of arginine, with catalytic efficiency increasing by 3.31-fold and 3.08-fold when exposed to 0.2 M and 0.3 M arginine, respectively. Additionally, arginine improved the thermal stability of Renilla luciferase. Molecular dynamics simulation showed that the addition of 0.2 M arginine reduced the binding of coelenteramide, the reaction product and an enzyme inhibitor, to the active site of the Renilla luciferase. Therefore, the release of the product was accelerated, and the affinity of Renilla luciferase for coelenterazine increased. Furthermore, Molecular dynamics studies indicated an increased network of water molecules surrounding Renilla luciferase in the presence of 0.2 M arginine. This network potentially enhances the hydrophobic effect on the protein structure, ultimately improving enzyme stability. The findings of this study hold promise for the development of commercial kits incorporating Renilla luciferase.

Host cell proteins in monoclonal antibody processing: Control, detection, and removal

Host cell proteins (HCPs) are process-related impurities in a therapeutic protein expressed using cell culture technology. This review presents biopharmaceutical industry trends in terms of both HCPs in the bioprocessing of monoclonal antibodies (mAbs) and the capabilities for HCP clearance by downstream unit operations. A comprehensive assessment of currently implemented and emerging technologies in the manufacturing processes with extensive references was performed. Meta-analyses of published downstream data were conducted to identify trends. Improved analytical methods and understanding of "high-risk" HCPs lead to more robust manufacturing processes and higher-quality therapeutics. The trend of higher cell density cultures leads to both higher mAb expression and higher HCP levels. However, HCP levels can be significantly reduced with improvements in operations, resulting in similar concentrations of approx. 10 ppm HCPs. There are no differences in the performance of HCP clearance between recent enhanced downstream operations and traditional batch processing. This review includes best practices for developing improved processes.

Ultrasound-assisted modification of soybean protein isolate with L-histidine: Relationship between structure and function

Herein, the effects of ultrasound-assisted L-histidine (L-His) on the physicochemical properties and conformation of soybean protein isolate (SPI) were investigated. Particle size, zeta potential, turbidity, and solubility were used to evaluate protein aggregation, and the relationship between structural and functional changes of the proteins was characterized using spectral analysis, surface hydrophobicity, emulsification, and antioxidant properties. After ultrasound-assisted L-His treatment, SPI exhibited a smaller particle size, higher solubility, and more homogeneous micromorphology owing to the decrease in alpha-helix content and subsequent increases in zeta potential and active sulfhydryl content. In addition, spectral analysis showed that L-His and SPI could form a complex, which changed the microenvironment of the amino acid residues in SPI, thus improving its emulsification and antioxidant properties. At the concentration of L-His was 0.3 % w/w, the nanocomplex had a smaller particle size (140.03 nm), higher ζ-potential (-23.63 mV), and higher emulsification stability (22.48 min).

Phenylalanine as an effective stabilizer and aggregation inhibitor of Bacillus amyloliquefaciens alpha-amylase

Aromatic compounds are known anti-amyloid aggregates. Their effect on amorphous aggregates of proteins is, however, less studied. We chose aromatic amino acids Trp, Tyr, and Phe, as well as another known stabilizer (i.e. Arg), as potential compatible solvents to be tested on Bacillus amyloliquefaciens alpha-amylase (BAA). Among these additives, Phe was the only one to be effective on the thermal inactivation and amorphous aggregation of BAA, while preserving its intrinsic activity. A concentration of 50 mM Phe was used to test its potential in counteracting the deleterious effect of BAA amorphous aggregates in vivo. After 21 days of daily subcutaneous injections of the native enzyme to mice, amorphous aggregates of BAA, as well as aggregates produced in presence of 50 mM Phe, the tissues located at the site of injection were studied histologically. Amorphous aggregates caused an increase in macrophages and lipid droplets. Serum levels of IL6 and TNF-α were also accordingly elevated and indicative of an inflammation state. Aggregates also resulted into increased levels of glucose, triglycerides and cholesterol, as well as liver enzymes SGOT and SGPT. On the other hand, the presence of Phe prevented this exacerbated inflammatory state and the subsequent impairment of biochemical parameters. In conclusion, Phe is an interesting compound for both stabilizing proteins and counteracting the pathological effect of amorphous aggregates.

Effects of trimer repeats on Psidium guajava L. gene expression and prospection of functional microsatellite markers

Most research on trinucleotide repeats (TRs) focuses on human diseases, with few on the impact of TR expansions on plant gene expression. This work investigates TRs' effect on global gene expression in Psidium guajava L., a plant species with widespread distribution and significant relevance in the food, pharmacology, and economics sectors. We analyzed TR-containing coding sequences in 1,107 transcripts from 2,256 genes across root, shoot, young leaf, old leaf, and flower bud tissues of the Brazilian guava cultivars Cortibel RM and Paluma. Structural analysis revealed TR sequences with small repeat numbers (5-9) starting with cytosine or guanine or containing these bases. Functional annotation indicated TR-containing genes' involvement in cellular structures and processes (especially cell membranes and signal recognition), stress response, and resistance. Gene expression analysis showed significant variation, with a subset of highly expressed genes in both cultivars. Differential expression highlighted numerous down-regulated genes in Cortibel RM tissues, but not in Paluma, suggesting interplay between tissues and cultivars. Among 72 differentially expressed genes with TRs, 24 form miRNAs, 13 encode transcription factors, and 11 are associated with transposable elements. In addition, a set of 20 SSR-annotated, transcribed, and differentially expressed genes with TRs was selected as phenotypic markers for Psidium guajava and, potentially for closely related species as well.

The search for novel proline analogs for viscosity reduction and stabilization of highly concentrated monoclonal antibody solutions

Administration of monoclonal antibodies (mAbs) is currently focused on subcutaneous injection associated with increased patient adherence and reduced treatment cost, leading to sustainable healthcare. The main bottleneck is low volume that can be injected, requiring highly concentrated mAb solutions. The latter results in increased solution viscosity with pronounced mAb aggregation propensity because of intensive protein-protein interactions. Small molecule excipients have been proposed to restrict the protein-protein interactions, contributing to reduced viscosity. The aim of the study was to discover novel compounds that reduce the viscosity of highly concentrated mAb solution. First, the chemical space of proline analogs was explored and 35 compounds were determined. Viscosity measurements revealed that 18 proline analogs reduced the mAb solution viscosity similar to or more than proline. The compounds forming both electrostatic and hydrophobic interactions with mAb reduced the viscosity of the formulation more efficiently without detrimentally effecting mAb physical stability. A correlation between the level of interaction and viscosity-reducing effect was confirmed with molecular dynamic simulations. Structure rigidity of the compounds and aromaticity contributed to their viscosity-reducing effect, dependent on molecule size. The study results highlight the novel proline analogs as an effective approach in viscosity reduction in development of biopharmaceuticals for subcutaneous administration.

Reexamining the diverse functions of arginine in biochemistry

Arginine in a free-state and as part of peptides and proteins shows distinct tendency to form clusters. In free-form, it has been found useful in cryoprotection, as a drug excipient for both solid and liquid formulations, as an aggregation suppressor, and an eluent in protein chromatography. In many cases, the mechanisms by which arginine acts in all these applications is either debatable or at least continues to attract interest. It is quite possible that arginine clusters may be involved in many such applications. Furthermore, it is possible that such clusters are likely to behave as intrinsically disordered polypeptides. These considerations may help in understanding the roles of arginine in diverse applications and may even lead to better strategies for using arginine in different situations.

Mathematical modeling of optimal coagulant dosage for tofu preparation using MgCl2

To explore the association between the optimal coagulant for tofu and the components of soybeans,30 different kinds of soybeans were selected, and tested for their optimal coagulant MgCl2 content. The optimal amount of coagulant was taken as the dependent variable, and the soybean Composition were taken as independent variables for the correlation analysis. The results showed that there was a positive correlation between the optimal coagulant content and the content of histidine, 7S β-conglycinin, B1aB1bB2B3B4 of 11 s glycincin, and α'-subunit of 7S β-conglycinin, negative correlation with lysine. The regression formula is y = -1.186 + 3.457*B1aB1bB2B3B4 + 2.304*7S + 0.351*histidine - 0.084*lysine + 4.696*α', and the model is validated to be within 10 % of the error value and has a high degree of confidence. This study provides theoretical support for realizing the green production of traditional soybean products.

Mechanism of Protein Aggregation Inhibition by Arginine: Blockage of Anionic Side Chains Favors Unproductive Encounter Complexes

Aggregation refers to the assembly of proteins into nonphysiological higher order structures. While amyloid has been studied extensively, much less is known about amorphous aggregation, a process that interferes with protein expression and storage. Free arginine (Arg+) is a widely used aggregation inhibitor, but its mechanism remains elusive. Focusing on myoglobin (Mb), we recently applied atomistic molecular dynamics (MD) simulations for gaining detailed insights into amorphous aggregation (Ng J. Phys. Chem. B 2021, 125, 13099). Building on that approach, the current work for the first time demonstrates that MD simulations can directly elucidate aggregation inhibition mechanisms. Comparative simulations with and without Arg+ reproduced the experimental finding that Arg+ significantly decreased the Mb aggregation propensity. Our data reveal that, without Arg+, protein-protein encounter complexes readily form salt bridges and hydrophobic contacts, culminating in firmly linked dimeric aggregation nuclei. Arg+ promotes the dissociation of encounter complexes. These "unproductive" encounter complexes are favored because Arg+ binding to D- and E- lowers the tendency of these anionic residues to form interprotein salt bridges. Side chain blockage is mediated largely by the guanidinium group of Arg+, which binds carboxylates through H-bond-reinforced ionic contacts. Our MD data revealed Arg+ self-association into a dynamic quasi-infinite network, but we found no evidence that this self-association is important for protein aggregation inhibition. Instead, aggregation inhibition by Arg+ is similar to that mediated by free guanidinium ions. The computational strategy used here should be suitable for the rational design of aggregation inhibitors with enhanced potency.

Amino acids and glycine derivatives differently affect refolding of mesophilic and thermophilic like α-amylases: implications in protein refolding and aggregation

α-amylases are industrially important enzymes which are used in different starch-based industries. They are adapted to different environmental conditions like extremes of temperature, pH and salinity. Herein, α-amylases from Bacillus amyloliquifaciens (BAA) and Bacillus licheniformis (BLA), representing mesophilic and thermophilic-like proteins, respectively, have been used to investigate the effect of naturally occurring osmolytes like arginine, proline, glycine and its methyl derivatives, sarcosine and betaine on their refolding. In this study, we have shown that among amino acids and glycine derivatives, betaine is the most promising osmolyte, while arginine and glycine exhibit moderately positive effect at their lower concentrations on the refolding of BAA only. Except betaine, all other osmolytes above 0.25 M showed inhibitory effect on the native enzyme activity of BLA and BAA. However, aggregation kinetics monitored by static light scattering indicates suppression of aggregation by all of these osmolytes. Further investigation by tryptophan and ANS fluorescence spectroscopy indicates the formation of compact hydrophobic core in the presence of the osmolytes. The morphology of protein aggregates having different sizes was visualized by atomic force microscopy ,and it was observed that amorphous aggregates of variable heights were formed. Our study highlights the importance of differential effects of arginine, proline, glycine, sarcosine and betaine on the native state as well as on refolding of BLA and BAA which may be helpful in devising strategies for developing effective protein formulation and prevention of aggregation of industrially and therapeutically important proteins.

Accelerated development of a SEC-HPLC procedure for purity analysis of monoclonal antibodies using design of experiments

The complex structure of biopharmaceutical products poses an inherent need for their thorough characterization to ensure product quality, safety, and efficacy. Analytical size exclusion chromatography (SEC) is a widely used technique throughout the development and manufacturing of monoclonal antibodies (mAbs) which quantifies product size variants such as aggregates and fragments. Aggregate and fragment content are critical quality attributes (CQAs) in mAb products, as higher contents of such size heterogeneities impact product quality. Historically, SEC methods have achieved sufficient separation between the high molecular weight (HMW) species and the main product. In contrast, some low molecular weight (LMW) species are often not sufficiently different in molecular mass from the main product, making it difficult to achieve appropriate resolutions between the two species. This lack of resolution makes it difficult to consistently quantify the LMW species in mAb-based therapeutics. The following work uses a design of experiments (DoE) approach to establish a robust analytical SEC procedure by evaluating SEC column types and mobile phase compositions using two mAb products with different physiochemical properties. The resulting optimized procedure using a Waters™ BioResolve column exhibits an improved ability to resolve and quantify mAb size variants, highlighting improvement in the resolution of the LMW species. Additionally, the addition of L-arginine as a mobile phase additive showed to reduce secondary interactions and was beneficial in increasing the recoveries of the HMW species.

Systematic enhancement of protein crystallization efficiency by bulk lysine-to-arginine (KR) substitution

Structural genomics consortia established that protein crystallization is the primary obstacle to structure determination using x-ray crystallography. We previously demonstrated that crystallization propensity is systematically related to primary sequence, and we subsequently performed computational analyses showing that arginine is the most overrepresented amino acid in crystal-packing interfaces in the Protein Data Bank. Given the similar physicochemical characteristics of arginine and lysine, we hypothesized that multiple lysine-to-arginine (KR) substitutions should improve crystallization. To test this hypothesis, we developed software that ranks lysine sites in a target protein based on the redundancy-corrected KR substitution frequency in homologs. This software can be run interactively on the worldwide web at https://www.pxengineering.org/. We demonstrate that three unrelated single-domain proteins can tolerate 5-11 KR substitutions with at most minor destabilization, and, for two of these three proteins, the construct with the largest number of KR substitutions exhibits significantly enhanced crystallization propensity. This approach rapidly produced a 1.9 Å crystal structure of a human protein domain refractory to crystallization with its native sequence. Structures from Bulk KR-substituted domains show the engineered arginine residues frequently make hydrogen-bonds across crystal-packing interfaces. We thus demonstrate that Bulk KR substitution represents a rational and efficient method for probabilistic engineering of protein surface properties to improve crystallization.

N-acetyl amino acid amide solubility in aqueous 1,6-hexanediol solutions: Insights into the protein droplet deformation mechanism

Proteinaceous liquid droplets, generated by liquid-liquid phase separation, function as membraneless compartments that are essential for diverse biological functions. Studies addressing droplet generation have used 1,6-hexanediol (1,6-HD) as a droplet-discerning agent owing to its capacity to induce droplet deformation. Despite the empirical utility of 1,6-HD, the mechanism underlying 1,6-HD-induced droplet deformation remains unknown. In this study, the solubilities of N-acetyl amino acid amides, which correspond to proteinogenic amino acid residues, were examined in the presence of 1,6-HD at 25 °C. Other solvents included ethanol, 1-propanol, and amides. Remarkably, 1,6-HD effectively solubilized hydrophobic species (particularly aromatic species) and exhibited reduced efficacy in solubilizing hydrophilic species and peptide bond moieties. These solubilizing effects are reflected in changes in protein solubility and structure. Specifically, 1,6-HD primarily targets the hydrophobic regions of a protein, increasing protein solubility without causing substantial structural changes. This solubilization mechanism is essential for elucidating the role of 1,6-HD as a droplet-discerning agent and recognizing its potential limitations.

Enzymatic and synthetic regulation of polypeptide folding

Proper folding is essential for the biological functions of all proteins. The folding process is intrinsically error-prone, and the misfolding of a polypeptide chain can cause the formation of toxic aggregates related to pathological outcomes such as neurodegenerative disease and diabetes. Chaperones and some enzymes are involved in the cellular proteostasis systems that assist polypeptide folding to diminish the risk of aggregation. Elucidating the molecular mechanisms of chaperones and related enzymes is important for understanding proteostasis systems and protein misfolding- and aggregation-related pathophysiology. Furthermore, mechanistic studies of chaperones and related enzymes provide important clues to designing chemical mimics, or chemical chaperones, that are potentially useful for recovering proteostasis activities as therapeutic approaches for treating and preventing protein misfolding-related diseases. In this Perspective, we provide a comprehensive overview of the latest understanding of the folding-promotion mechanisms by chaperones and oxidoreductases and recent progress in the development of chemical mimics that possess activities comparable to enzymes, followed by a discussion of future directions.

Scalable production of recombinant three-finger proteins: from inclusion bodies to high quality molecular probes

BACKGROUND

The three-finger proteins are a collection of disulfide bond rich proteins of great biomedical interests. Scalable recombinant expression and purification of bioactive three-finger proteins is quite difficult.

RESULTS

We introduce a working pipeline for expression, purification and validation of disulfide-bond rich three-finger proteins using E. coli as the expression host. With this pipeline, we have successfully obtained highly purified and bioactive recombinant α-Βungarotoxin, k-Bungarotoxin, Hannalgesin, Mambalgin-1, α-Cobratoxin, MTα, Slurp1, Pate B etc. Milligrams to hundreds of milligrams of recombinant three finger proteins were obtained within weeks in the lab. The recombinant proteins showed specificity in binding assay and six of them were crystallized and structurally validated using X-ray diffraction protein crystallography.

CONCLUSIONS

Our pipeline allows refolding and purifying recombinant three finger proteins under optimized conditions and can be scaled up for massive production of three finger proteins. As many three finger proteins have attractive therapeutic or research interests and due to the extremely high quality of the recombinant three finger proteins we obtained, our method provides a competitive alternative to either their native counterparts or chemically synthetic ones and should facilitate related research and applications.

Biological importance of arginine: A comprehensive review of the roles in structure, disorder, and functionality of peptides and proteins

Arginine shows Jekyll and Hyde behavior in several respects. It participates in protein folding via ionic and H-bonds and cation-pi interactions; the charge and hydrophobicity of its side chain make it a disorder-promoting amino acid. Its methylation in histones; RNA binding proteins; chaperones regulates several cellular processes. The arginine-centric modifications are important in oncogenesis and as biomarkers in several cardiovascular diseases. The cross-links involving arginine in collagen and cornea are involved in pathogenesis of tissues but have also been useful in tissue engineering and wound-dressing materials. Arginine is a part of active site of several enzymes such as GTPases, peroxidases, and sulfotransferases. Its metabolic importance is obvious as it is involved in production of urea, NO, ornithine and citrulline. It can form unusual functional structures such as molecular tweezers in vitro and sprockets which engage DNA chains as part of histones in vivo. It has been used in design of cell-penetrating peptides as drugs. Arginine has been used as an excipient in both solid and injectable drug formulations; its role in suppressing opalescence due to liquid-liquid phase separation is particularly very promising. It has been known as a suppressor of protein aggregation during protein refolding. It has proved its usefulness in protein bioseparation processes like ion-exchange, hydrophobic and affinity chromatographies. Arginine is an amino acid, whose importance in biological sciences and biotechnology continues to grow in diverse ways.

Evaluation of novel chromatographic prototypes for supercoiled plasmid DNA polishing

Since the world first approved gene therapeutics, nucleic acid-based therapies have gained prominence. Several strategies for DNA-based therapy have been approved, and numerous clinical trials for plasmid DNA (pDNA)-based vaccines are currently in development. Due to the rising interest in pDNA for vaccination and gene therapy, plasmid manufacturing must become more effective. One of the most critical steps is downstream processing, involving isolation and purification procedures. To comply with the regulatory guidelines, pDNA must be available as a highly purified, homogeneous preparation of supercoiled pDNA (sc pDNA). This process undertakes several challenges, primarily due to the diversity of molecules derived from the producer organism. In this study, different resins were tested for the adsorption and selective polishing of sc pDNA. To identify optimal pDNA adsorption conditions, batch and column assays were performed with different resins while promoting electrostatic and hydrophobic interactions. The effect of ionic strength, pH, and contact time were evaluated and optimized. Additionally, static and dynamic binding capacities were determined for the selected resins. Analytical chromatography and agarose gel electrophoresis were used to assess the selectivity of the most promising resins toward sc pDNA isoform. Also, genomic DNA, endotoxins, and proteins were quantified to characterize the final sc pDNA quality. At the same time, the recovery and purity yields were evaluated by quantification of sc pDNA after the purification procedure. Overall, the results of the chromatographic assays using agmatine- and arginine-based resins have shown promising potential for sc pDNA polishing. Both resins demonstrated excellent binding capacity for pDNA, with agmatine outperforming arginine-based resin in terms of capacity. However, arginine-based resin exhibited a superior pDNA recovery yield, reaching a notable 52.2% recovery compared to 10.09% from agmatine. Furthermore, both resins exhibited high relative purity levels above 90% for the sc pDNA. The comprehensive characterization of the recovered sc pDNA also revealed a significant reduction in gDNA levels, reinforcing the potential of these prototypes for obtaining high-quality and pure sc pDNA. These findings highlight the promising applications of both resins in scalable pDNA purification processes for gene therapy and biopharmaceutical applications.

Effects of Amino Acid Additives on Protein Stability during Electrothermal Supercharging in ESI-MS

The surprising formation of highly charged protein ions from aqueous ammonium bicarbonate solution is a fascinating phenomenon referred to as electrothermal supercharging (ETS). Although the precise mechanism involved is not clearly understood, previous studies predominantly suggest that ETS is due to native protein destabilization in the presence of bicarbonate anion inside the electrospray ionization droplets under high temperatures and spray voltages. To evaluate existing hypotheses surrounding the underlying mechanism of ETS, the effects of several additives on protein charging under ETS conditions were investigated. The changes in the protein charge state distributions were compared by measuring the ratios between the intensities of highest intensity charge states of native and unfolded protein envelopes and shifts in the lowest and highest observed charge states. This study demonstrated that source temperature plays a more important role in ETS compared to spray voltage, especially when using a nebulized microelectrospray ionization source. Moreover, the effect of amino acids on ETS were generally in good agreement with the extensive literature available on the stabilization or destabilization of proteins by these additives in bulk solution. Among the natural amino acids, protein supercharging was significantly reduced by proline and glycine; however, imidazole provided the highest degree of noncovalent complex stabilization against ETS, outperforming the amino acids. Overall, our study shows that the simple addition of stabilizing reagents such as proline and imidazole can reduce the extent of apparent protein unfolding and supercharging in ammonium bicarbonate solution and provide evidence against the roles of charge depletion and thermal unfolding during ETS.

Synthesis of Butterfly-Like Shaped Gold Nanomaterial: For the Regulation of Liquid-Liquid Phase-Separated Biomacromolecule Droplets

Nanotechnology is a critical tool to manipulate the sophisticated behavior of biological structures and has provided new research fields. Liquid-liquid phase-separated (LLPS) droplets gather attention as basic reaction fields in a living cell. Droplets play critical roles in regulating protein behavior, including enzyme compartmentalization, stress response, and disease pathogenesis. The dynamic manipulation of LLPS droplet formation/deformation has become a crucial target in nanobiotechnology. However, the development of nanodevices specifically designed for this purpose remains a challenge. Therefore, this study presents butterfly-shaped gold nanobutterflies (GNBs) as novel nanodevices for manipulating LLPS droplet dynamics. The growth process of the GNBs is analyzed via time-lapse electroscopic imaging, time-lapse spectroscopy, and additives assays. Interestingly, GNBs demonstrate the ability to induce LLPS droplet formation in systems such as adenosine triphosphate/poly-l-lysine and human immunoglobulin G, whereas spherical and rod-shaped gold nanoparticles exhibit no such capability. This indicates that the GNB concave surface interacts with the droplet precursors facilitating the LLPS droplet formation. Near-infrared-laser irradiation applied to GNBs enables on-demand deformation of the droplets through localized heat effects. GNB regulates the enzymatic reaction of lysozymes. The innovative design of GNBs presents a promising strategy for manipulating LLPS dynamics and offers exciting prospects for future research.

A comprehensive evaluation of arginine and its derivatives as protein formulation stabilizers

Arginine and its derivatives (such as arginine ethyl ester and acetyl arginine) have varying degrees of protein aggregation suppressor effect across different protein solutions. To understand this performance ambiguity, we evaluated the activity of arginine, acetyl arginine, and arginine ethyl ester for aggregation suppressor effect against human intravenous immunoglobulin G (IgG) solution at pH 4.8. Both arginine and its cationic derivative arginine ethyl ester in their hydrochloride salt forms significantly reduced the colloidal and conformational stability (reduced kd and Tm) of IgG. Consequently, the monomer content was decreased with an increase in subvisible particulates after agitation or thermal stress. Furthermore, compared to arginine, arginine ethyl ester with one more cationic charge and hydrochloride salt form readily precipitated IgG at temperatures higher than 25 °C. On the contrary, acetyl arginine, which mostly exists in a neutral state at pH 4.8, efficiently suppressed the formation of subvisible particles retaining a high amount of monomer owing to its higher colloidal and conformational stability. Concisely, the charged state of additives significantly impacts protein stability. This study demonstrated that contrary to popular belief, arginine and its derivatives may either enhance or suppress protein aggregation depending on their net charge and concentration.

Application of Formulation Principles to Stability Issues Encountered During Processing, Manufacturing, and Storage of Drug Substance and Drug Product Protein Therapeutics

The field of formulation and stabilization of protein therapeutics has become rather extensive. However, most of the focus has been on stabilization of the final drug product. Yet, proteins experience stress and degradation through the manufacturing process, starting with fermentaition. This review describes how formulation principles can be applied to stabilize biopharmaceutical proteins during bioprocessing and manufacturing, considering each unit operation involved in prepration of the drug substance. In addition, the impact of the container on stabilty is discussed as well.

An investigation of excipients for a stable Orf viral vector formulation

The Orf virus (ORFV) is a promising candidate for vector vaccines as well as for immunomodulatory and oncolytic therapies. However, few publications are available on its infectivity degradation or on suitable additives for prolonging its viral stability. In this study, the non-supplemented ORFV itself showed a very high stability at storage temperatures up to 28 °C, with a linear titer loss of 0.10 log infectious particles per day at 4 °C over a period of five weeks. To prolong this inherent stability, thirty additives, i.e., detergents, sugars, proteins, salts, and buffers as well as amino acids, were tested for their time- and temperature-dependent influence on the ORFV infectivity. A stabilizing effect on the infectivity was identified for the addition of all tested proteins, i.e., gelatine, bovine serum albumin, and recombinant human serum albumin (rHSA), of several sugars, i.e., mannitol, galactose, sucrose, and trehalose, of amino acids, i.e., arginine and proline, of the detergent Pluronic F68, and of the salt Na2SO4. The infectivity preservation was especially pronounced for proteins in liquid and frozen formulations, sugars in frozen state, and arginine und Pluronic in liquid formulations at high storage temperatures (37 °C). The addition of 1% rHSA with and without 5% sucrose was evaluated as a very stable formulation with a high safety profile and economic validity at storage temperatures up to 28 °C. At increased temperatures, the supplementation with 200 mM arginine performed better than with rHSA. In summary, this comprehensive data provides different options for a stable ORFV formulation, considering temperature, storage time, economic aspects, and downstream processing integrity.

Mechanistic Insight into Poly-Reactivity of Immune Antibodies upon Acid Denaturation or Arginine Mutation in Antigen-Binding Regions

The poly-reactivity of antibodies is defined as their binding to specific antigens as well as to related proteins and also to unrelated targets. Poly-reactivity can occur in individual molecules of natural serum antibodies, likely due to their conformation flexibility, and, for therapeutic antibodies, it plays a critical role in their clinical development. On the one hand, it can enhance their binding to target antigens and cognate receptors, but, on the other hand, it may lead to a loss of antibody function by binding to off-target proteins. Notably, poly-reactivity has been observed in antibodies subjected to treatments with dissociating, destabilizing or denaturing agents, in particular acidic pH, a common step in the therapeutic antibody production process involving the elution of Protein-A bound antibodies and viral clearance using low pH buffers. Additionally, poly-reactivity can emerge during the affinity maturation in the immune system, such as the germinal center. This review delves into the underlying potential causes of poly-reactivity, highlighting the importance of conformational flexibility, which can be further augmented by the acid denaturation of antibodies and the introduction of arginine mutations into the complementary regions of antibody-variable domains. The focus is placed on a particular antibody's acid conformation, meticulously characterized through circular dichroism, differential scanning calorimetry, and sedimentation velocity analyses. By gaining a deeper understanding of these mechanisms, we aim to shed light on the complexities of antibody poly-reactivity and its implications for therapeutic applications.

Viscosity Prediction of High-Concentration Antibody Solutions with Atomistic Simulations

The computational prediction of the viscosity of dense protein solutions is highly desirable, for example, in the early development phase of high-concentration biopharmaceutical formulations where the material needed for experimental determination is typically limited. Here, we use large-scale atomistic molecular dynamics (MD) simulations with explicit solvation to de novo predict the dynamic viscosities of solutions of a monoclonal IgG1 antibody (mAb) from the pressure fluctuations using a Green-Kubo approach. The viscosities at simulated mAb concentrations of 200 and 250 mg/mL are compared to the experimental values, which we measured with rotational rheometry. The computational viscosity of 24 mPa·s at the mAb concentration of 250 mg/mL matches the experimental value of 23 mPa·s obtained at a concentration of 213 mg/mL, indicating slightly different effective concentrations (or activities) in the MD simulations and in the experiments. This difference is assigned to a slight underestimation of the effective mAb-mAb interactions in the simulations, leading to a too loose dynamic mAb network that governs the viscosity. Taken together, this study demonstrates the feasibility of all-atom MD simulations for predicting the properties of dense mAb solutions and provides detailed microscopic insights into the underlying molecular interactions. At the same time, it also shows that there is room for further improvements and highlights challenges, such as the massive sampling required for computing collective properties of dense biomolecular solutions in the high-viscosity regime with reasonable statistical precision.

Effects of arginine in therapeutic protein formulations: a decade review and perspectives

Arginine (Arg) is a natural amino acid with an acceptable safety profile and a unique chemical structure. Arg and its salts are highly effective in enhancing protein refolding and solubilization, suppressing protein-protein interaction and aggregation and reducing viscosity of high concentration protein formulations. Arg and its salts have been used in research and 20 approved protein injectables. This review summarizes the effects of Arg as an excipient in therapeutic protein formulations with the focus on its physicochemical properties, safety, applications in approved protein products, beneficial and detrimental effects in liquid and lyophilized protein formulations when combined with different counterions and mechanism on protein stabilization and destabilization. The decade literature review indicates that the benefits of Arg overweigh its risks when it is used appropriately. It is recommended to add Arg along with glutamate as a counterion to high concentration protein formulations on top of sugars or polyols to counterbalance the negative effects of Arg hydrochloride. The use of Arg as a viscosity reducer and protein stabilizer in high concentration formulations will be the inevitable future trend of the biopharmaceutical industry for subcutaneous administration.

L-Arginine sulfate reduces irreversible protein binding in immobilized metal affinity chromatography

Immobilized metal affinity chromatography (IMAC) is a powerful technique for capture and purification of relevant biopharmaceuticals in complex biological matrices. However, protein recovery can be drastically compromised due to surface induced spreading and unfolding of the analyte, leading to fouling of the stationary phase. Here, we report on the kinetics of irreversible adsorption of a protease on an IMAC resin in a time span ranging from minutes to several hours. This trend correlated with the thermal data measured by nano differential scanning calorimetry, and showed a time-dependent change in protein unfolding temperature. Our results highlight that 'soft' proteins show a strong time dependent increase in irreversible adsorption. Furthermore, commonly used co-solvents for preservation of the native protein conformation are tested for their ability to reduce fouling. Thermal data suggests that the amino acid l-arginine is beneficial in preventing unfolding, which was confirmed in batch adsorption experiments. The choice of counter-ions has to be considered when using this amino acid. These results show that l-arginine sulfate decelerates the irreversible adsorption kinetics of proteins on the IMAC stationary phase to a greater extent than l-arginine chloride.

L-lysine moderates thermal aggregation of coconut proteins induced by thermal treatment

This work attempts to investigate the inhibitory effect of L-lysine (Lys) on the thermal aggregation of coconut protein (CP). The results showed that under neutral conditions (pH = 7), temperature reduced the solubility and enhanced the thermally induced gel formation of CP. In addition, Lys reduced the fluorescence properties, particle size and increased the turbidity of CP, which had an inhibitory effect on heat induced gels. The results indicate that Lys plays an important role in inhibiting protein thermal aggregation by interacting with CP to create steric hindrance and increase protein electrostatic repulsion.