The effects of arginine on refolding of aggregated proteins: not facilitate refolding, but suppress aggregation

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.

The research on the synergistic improvement of water retention capacity and eating quality of marinated pork meat by the combination of basic arginine and acidic aspartic acid

Effects of varying levels of arginine (Arg) and aspartic acid (Asp) on the water-holding capacity (WHC) and eating quality of marinated pork meat were investigated. The addition of Arg significantly enhanced the WHC of marinated pork meat (P < 0.05) due to the increased pH levels of the meat. Besides, when the pH values of the meat were consistent, the combined use of Arg and Asp significantly decreased the cooking loss (CL) from 9.0 % to 6.4 % (P < 0.05) and increased the hardness and springiness (P < 0.05). These outcomes could be attributed to the combined effects of Arg and Asp, which promoted the dissociation of actomyosin and enhanced the antioxidant capacity of proteins, leading to a significant increase in the ordered structure. Moreover, Asp affected the extensibility of the perimysium, improving the tightness between fiber bundles. These modifications in muscle structures improved the WHC and texture of the meat.

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.

Basic Amino Acids as Salt Substitutes in Low-Salt Gel-Based Meat Products: A Comprehensive Review of Mechanisms, Benefits, and Future Perspectives

Gel-based meat products have appealing market potential due to their unique texture, elasticity, and tender taste. Sodium chloride (NaCl) is commonly used in these products to enhance flavor, improve texture, ensure food safety, and extend shelf life. However, excessive long-term NaCl intake is connected with health issues such as hypertension and cardiovascular diseases, raising concerns about its impact on human health. As a result, the reduction of NaCl in these products, while maintaining their flavor and texture, has become a key area in the food industry. Salt reduction strategies often compromise product quality, limiting the search for substitutes. Consequently, there is growing interest in developing new salt substitutes. Recently, basic amino acids (BAA) have emerged as a viable alternative to NaCl in low-salt gel-based meat products. Studies have shown that BAAs not only enhance the solubility, gelation, and emulsification properties of salt-soluble proteins but also reduce protein and lipid oxidation in low-salt conditions, improving sensory characteristics and texture. When combined with chloride salts, BAAs can further lower salt content while improving the quality of the products. In addition, adding modern processing techniques (such as ultrasound, pulsed electric fields) has indicated positive effects on the taste and texture of low-salt meat products. Future studies should deploy advanced tools to dissect the micro-/macro-level impacts of BAAs on low-salt gel products. Furthermore, integrating modern food processing and information technologies could lead to the development of personalized, intelligent low-salt meat products that satisfy consumer demands for both health and taste.

Exploring non-alcohol-based disinfectant: virucidal efficacy of arginine and Zinc chloride against feline calicivirus

Introduction

Norovirus, a leading cause of acute gastroenteritis worldwide, is notably stable in the environment due to its non-enveloped nature. In the absence of effective vaccines or treatments, disinfection remains the primary prevention strategy, highlighting the importance of virucidal efficacy in household care products. Conventional effective disinfectants are predominantly alcohol-based, but alcohol is known to pose health risks, such as skin irritation. This study investigates a non-alcohol-based alternative, specifically a combination of Arginine and Zinc chloride (ZnCl2).

Methods

Utilizing MS2 bacteriophage as a surrogate, we identified a robust combination of arginine and ZnCl2 that is effective against Feline Calicivirus (FCV), a mammalian virus surrogate model for Norovirus.

Results

Our results determined a 5 min contact time at pH 11 as optimal, achieving significant virucidal activity against FCV without pH-induced reversibility. Dynamic Light Scattering (DLS) and transmission electron microscopy (TEM) analyses suggested that the mechanism of action for the Arg-Zn2+-Arg complex does not involve capsid disruption. Further insights from molecular modeling studies revealed that the complex potentially inhibits FCV by occupying a key capsid binding pocket essential for Junctional Adhesion Molecule (JAM) receptor engagement, thereby preventing viral entry.

Conclusion

These findings allow us to propose a novel and non-alcohol-based virucidal approach against viruses from the Caliciviridae family, highlighting the potential of Arg-Zn2+-Arg complexes in public health protection.

A universal method for the purification of C2H2 zinc finger arrays

Zinc fingers (ZFs) are compact, modular, sequence-specific polynucleotide-binding domains uniquely suited for use as DNA probes and for the targeted delivery of effector domains for purposes such as gene regulation and editing. Despite recent advances in both the design and application of ZF-containing proteins, there is still a lack of a general method for their expression and purification. Here we describe a simple method, involving two chromatographic steps, for the production of homogeneous, functional ZF proteins in high yield (one milligram per liter of bacterial culture), and we demonstrate the generality of this method by applying it to a diverse set of eight C2H2-type ZF proteins. By incorporating a surface-exposed terminal cysteine residue that enables site-specific conjugation with maleimide-activated fluorophores, we confirm the suitability of these probes for in situ labeling of specific DNA sequences in human cells.

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.

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.

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.

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.

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.

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.

Interaction between preservatives and a monoclonal antibody in support of multidose formulation development

Multidose formulations have patient-centric advantages over single-dose formats. A major challenge in developing multidose formulations is the prevention of microbial growth that can potentially be introduced during multiple drawings. The incorporation of antimicrobial preservatives (APs) is a common approach to inhibit this microbial growth. Selection of the right preservative while maintaining drug product stability is often challenging. We explored the effects of three APs, 1.1 % (w/v) benzyl alcohol, 0.62 % (w/v) phenol, and 0.42 % (w/v) m-cresol, on a model immunoglobulin G1 monoclonal antibody, termed the "NIST mAb." As measured by hydrogen exchange-mass spectrometry (HX-MS) and differential scanning calorimetry, conformational stability was decreased in the presence of APs. Specifically, flexibility (faster HX) was significantly increased in the CH2 domain (HC 238-255) across all APs. The addition of phenol caused the greatest conformational destabilization, followed by m-cresol and benzyl alcohol. Storage stability studies conducted by subvisible particle (SVP) analysis at 40 °C over 4 weeks further revealed an increase in SVPs in the presence of phenol and m-cresol but not in the presence of benzyl alcohol. However, as monitored by size exclusion chromatography, there was neither a significant change in the monomeric content nor an accumulation of soluble aggregate in the presence of APs.

Impact of L-arginine on the quality of heat-treated Antarctic krill: Influence of pH and the guanidinium group

Antarctic krill suffers from severe water loss after heating, and its quality deteriorates, so it is in urgent need of a green and healthy improver. In this paper, the effects of L-arginine (L-Arg) soaking on the modification of the quality of heat-treated Antarctic krill and the structure of myofibrillar proteins (MPs) in Antarctic krill were investigated. The results showed that L-Arg had an ameliorating effect on heat-treated krill in a concentration-dependent relationship. The water-holding capacity of L-Arg-soaked krill was 1.41 times higher than that of sodium tripolyphosphate (STPP) at an equivalent concentration (80 mM). At 120 mM L-Arg soaked, L* and hardness of krill decreased to 58.31 and 334.81 g, while resilience and moisture content increased to 0.47 and 85.29 % after heating, respectively. The scanning electron microscopy (SEM) results revealed that the tissue state of the pH-corrected groups was better than the control, but not as well as that of the pH-uncorrected groups. pH and the guanidinium group in L-Arg both played roles in promoting the transition of MPs from disordered to ordered secondary structures. This transition reduced the exposure of hydrophobic and sulfhydryl groups in MPs, inhibited the protein aggregation and increased the solubility of MPs to 71.61 %, which ultimately improved the quality of heat-treated krill. It is worth noting that the pH effect had a primary influence on the observed effects, while the guanidinium group made a secondary contribution. These results could broaden the potential application of L-Arg as an improver of the quality of heat-treated krill.

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.

Behavior, BDNF and epigenetic mechanisms in response to social isolation and social support in middle aged rats exposed to chronic stress

Social deprivation can be stressful for group-living mammals. On the other hand, an amazing response of these animals to stress is seeking social contact to give and receive joint protection in threatening situations. We explored the effects of social isolation and social support on epigenetic and behavioral responses to chronic stress. More specifically, we investigated the behavioral responses, corticosterone levels, BDNF gene expression, and markers of hippocampal epigenetic alterations (levels of H3K9 acetylation and methylation, H3K27 methylation, HDAC5, DNMT1, and DNMT3a gene expressions) in middle-aged adult rats maintained in different housing conditions (isolation or accompanied housing) and exposed to the chronic unpredictable stress protocol (CUS). Isolation was associated with decreased basal levels of corticosterone, impaired long-term memory, and decreased expression of the BDNF gene, besides altering the balance of H3K9 from acetylation to methylation and increasing the DNMT1 gene expression. The CUS protocol decreased H3K9 acetylation, besides increasing H3K27 methylation and DNMT1 gene expression, but had no significant effects on memory and BDNF gene expression. Interestingly, the effects of CUS on corticosterone and HDAC5 gene expression were seen only in isolated animals, whereas the effects of CUS on DNMT1 gene expression were more pronounced in isolated than accompanied animals. In conclusion, social isolation in middle age showed broader effects than chronic unpredictable stress on behavioral and epigenetic alterations potentially associated with decreased BDNF expression. Moreover, social support prevented the adverse effects of CUS on HPA axis functioning, HDAC5, and DNMT1 gene expressions.

Calcium-dependent affinity ligands for the purification of antibody fragments at neutral pH

The emerging formats of antibody fragments for biotherapeutics suffer from inadequate purification methods, delaying the advances of innovative therapies. One of the top therapeutic candidates, the single-chain variable fragment (scFv), requires the development of individual purification protocols dependent on the type of scFv. The available approaches that are based on selective affinity chromatography but do not involve the use of a purification tag, such as Protein L and Protein A chromatography, require acidic elution buffers. These elution conditions can cause the formation of aggregates and thereby greatly compromise the yield, which can be a major problem for scFvs that are generally unstable molecules. Due to the costly and time-consuming production of biological drugs, like antibody fragments, we have engineered novel purification ligands that elute the scFvs in a calcium-dependent manner. The developed ligands are equipped with new, selective binding surfaces and were shown to efficiently elute all captured scFv at neutral pH with the use of a calcium chelator. Further, two of three ligands were proven not to bind to the CDRs of the scFv, indicating potential for use as generic affinity ligands to a range of different scFvs. Multimerization and optimization of the most promising ligand led to a 3-fold increase in binding capacity for the hexamer compared to the monomer, in addition to highly selective and efficient purification of a scFv with >95% purity in a single purification step. This calcium-dependent ligand could revolutionize the scFv industry, greatly facilitating the purification procedure and improving the quality of the final product.

Non-Affinity Purification of Antibodies

Currently, purification of antibodies is mainly carried out using a platform technology composed primarily of Protein A chromatography as a capture step, regardless of the scale. However, Protein A chromatography has a number of drawbacks, which are summarized in this review. As an alternative, we propose a simple small-scale purification protocol without Protein A that uses novel agarose native gel electrophoresis and protein extraction. For large-scale antibody purification, we suggest mixed-mode chromatography that can in part mimic the properties of Protein A resin, focusing on 4-Mercapto-ethyl-pyridine (MEP) column chromatography.

Alternative Excipients for Protein Stabilization in Protein Therapeutics: Overcoming the Limitations of Polysorbates

Given their safety and efficiency in protecting protein integrity, polysorbates (PSs) have been the most widely used excipients for the stabilization of protein therapeutics for years. In recent decades, however, there have been numerous reports about visible or sub-visible particles in PS-containing biotherapeutic products, which is a major quality concern for parenteral drugs. Alternative excipients that are safe for parenteral administration, efficient in protecting different protein drugs against various stress conditions, effective in protein stabilization in high-concentrated liquid formulations, stable under the storage conditions for the duration of the product's shelf-life, and compatible with other formulation components and the primary packaging are highly sought after. The aim of this paper is to review potential alternative excipients from different families, including surfactants, carbohydrate- and amino acid-based excipients, synthetic amphiphilic polymers, and ionic liquids that enable protein stabilization. For each category, important characteristics such as the ability to stabilize proteins against thermal and mechanical stresses, current knowledge related to the safety profile for parenteral administration, potential interactions with other formulation components, and primary packaging are debated. Based on the provided information and the detailed discussion thereof, this paper may pave the way for the identification or development of efficient excipients for biotherapeutic protein stabilization.

Enhanced protein aggregation suppressor activity of N-acetyl-l-arginine for agitation-induced aggregation with silicone oil and its impact on innate immune responses

Previously, N-acetyl-l-arginine (NALA) suppressed the aggregation of intravenous immunoglobulins (IVIG) more effectively and with a minimum decrease in transition temperature (T_m) than arginine monohydrochloride. In this study, we performed a comparative study with etanercept (commercial product: Enbrel®), where 25 mM arginine monohydrochloride (arginine) was added to the prefilled syringe. The biophysical properties were investigated using differential scanning calorimetry (DSC), dynamic light scattering (DLS), size-exclusion chromatography (SEC), and flow-imaging microscopy (FI). NALA retained the transition temperature of etanercept better than arginine, where arginine significantly reduced the T_m by increasing its concentration. End-over-end rotation was applied to each formulation for 5 days to accelerate protein aggregation and subvisible particle formation. Higher monomeric content was retained with NALA with a decrease in particle level. Higher aggregation onset temperature (T_agg) was detected for etanercept with NALA than arginine. The results of this comparative study were consistent with previous study, suggesting that NALA could be a better excipient for liquid protein formulations. Agitated IVIG and etanercept were injected into C57BL/6 J female mice to observe immunogenic response after 24 h. In the presence of silicone oil, NALA dramatically reduced IL-1 expression, implying that decreased aggregation was related to reduced immunogenicity of both etanercept and IVIG.

The mechanism of thermal aggregation of glutamate dehydrogenase. The effect of chemical chaperones

Chemical chaperones are low-molecular compounds counteracting protein aggregation. Understanding of the mechanism of their effects is key to their potential use in biotechnology. The aggregation of bovine liver glutamate dehydrogenase (GDH) was studied at 40 °C and 50 °C using dynamic light scattering, analytical ultracentrifugation, size-exclusion chromatography and differential scanning calorimetry. At 40 °C the GDH aggregation proceeds through the slow stages of hexamer dissociation and formation of small oligomeric aggregates. At 50 °C these stages are transient. The rate-limiting stage of the overall aggregation process is unfolding of the protein molecule; the order of aggregation with respect to protein, n = 1. The test system based on GDH aggregation at 50 °C was used to quantify the anti-aggregation activity of chemical chaperones by comparing their half-saturation concentrations [L]_0.5. Arginine ethyl ester had the highest anti-aggregation activity, with [L]_0.5 = 4 ± 1 mM. For other additives, [L]_0.5 was 22 ± 1 mM (arginine), 18 ± 1 mM (argininamide) and 95 ± 12 mM (proline). Arginine at concentrations up to 300 mM, argininamide at concentrations higher than 300 mM and arginine ethyl ester at concentrations higher than 500 mM enhance aggregate-aggregate sticking. These results explain the mechanism of heat-induced GDH aggregation and its peculiarities at different temperatures or in the presence of chemical chaperones.

Investigating protein-excipient interactions of a multivalent VHH therapeutic protein using NMR spectroscopy

Multispecific therapeutic proteins come in a variety of formats, including bi- and tri-specific antibodies, dual-variable domain antibodies, and CrossMabs. These multivalent proteins are engineered to interact with multiple therapeutic target proteins with high specificity. Multi-domain proteins can be created by linking together a variety of high-affinity antibody fragments. The choice of protein domains and linkers not only affects the interactions of these molecules with therapeutic targets but also influences the intrinsic behavior in solution that affects their stability. The complexity of solution interactions may translate into developability and manufacturing challenges. Here, we use nuclear magnetic resonance (NMR) spectroscopy to study the solution behavior of a multivalent V_HH molecule composed of three flexibly linked heavy-chain-only domains that show dramatic stabilization against thermal degradation in the presence of sucrose. A collection of NMR fingerprinting and profiling methods were used to simultaneously monitor the protein solution behavior and capture details of protein–excipient interactions. We provide a framework to characterize and begin to understand the role of molecular flexibility in protein stabilization with potential applications in the design of novel therapeutic protein scaffolds that include multivalent proteins, fusion proteins, antibody-drug conjugates, and proteins modified with flexible lipids.

Kinetics theories to understand the mechanism of aggregation of a protein and to design strategies for its inhibition

Protein aggregation phenomenon is closely related to the formation of amyloids which results in many neurodegenerative diseases like Alzheimer's, Parkinson's, Huntington's, and Amyotrophic Lateral Sclerosis. In order to prevent and treat these diseases, a clear understanding of the mechanism of misfolding and self-assembly of peptides and proteins is very crucial. The aggregation of a protein may involve various microscopic events. Multiple simulations utilizing the solutions of the master equation have given a better understanding of the kinetic profiles involved in the presence and absence of a particular microscopic event. This review focuses on understanding the contribution of these molecular events to protein aggregation based on the analysis of kinetic profiles of aggregation. We also discuss the effect of inhibitors, which target various species of aggregation pathways, on the kinetic profile of protein aggregation. At the end of this review, some strategies for the inhibition of aggregation that can be utilized by combining the chemical kinetics approach with thermodynamics are proposed.

Anti-EGFR VHH Antibody under Thermal Stress Is Better Solubilized with a Lysine than with an Arginine SEP Tag

In this study, we assessed the potential of arginine and lysine solubility-enhancing peptide (SEP) tags to control the solubility of a model protein, anti-EGFR V_HH-7D12, in a thermally denatured state at a high temperature. We produced V_HH-7D12 antibodies attached with a C-terminal SEP tag made of either five or nine arginines or lysines (7D12-C5R, 7D12-C9R, 7D12-C5K and 7D12-C9K, respectively). The 5-arginine and 5-lysine SEP tags increased the E. coli expression of V_HH-7D12 by over 80%. Biophysical and biochemical analysis confirmed the native-like secondary and tertiary structural properties and the monomeric nature of all V_HH-7D12 variants. Moreover, all V_HH-7D12 variants retained a full binding activity to the EGFR extracellular domain. Finally, thermal stress with 45-minute incubation at 60 and 75 °C, where V_HH-7D12 variants are unfolded, showed that the untagged V_HH-7D12 formed aggregates in all of the four buffers, and the supernatant protein concentration was reduced by up to 35%. 7D12-C5R and 7D12-C9R did not aggregate in Na-acetate (pH 4.7) and Tris-HCl (pH 8.5) but formed aggregates in phosphate buffer (PB, pH 7.4) and phosphate buffer saline (PBS, pH 7.4). The lysine tags (either C5K or C9K) had the strongest solubilization effect, and both 7D12-C5K and 7D12-C9K remained in the supernatant. Altogether, our results indicate that, under a thermal stress condition, the lysine SEP tags solubilization effect is more potent than that of an arginine SEP tags, and the SEP tags did not affect the structural and functional properties of the protein.

Glass-like protein condensate for the long-term storage of proteins

Long-term storage of proteins at ambient temperature is required for applications in pharmaceutics and biotechnology. Lyophilization is a versatile approach for stabilizing proteins at ambient temperature, although its freezing and drying processes negatively affect the protein structure. In this study, we show a glass-like protein condensate (GLPC) as a new method for protein stabilization at ambient temperature. Various protein types, including immunoglobulin G, gamma globulin, albumin, and chymotrypsin, formed a glassy state during ultracentrifugation and natural drying, while proteins that tend to crystalize, such as hen egg-white lysozyme, did not. The GLPCs were characterized by a transparent solid state, similar to a dry glass ball. Importantly, the GLPCs were dissolved easily in saline solution at a physiological concentration, thereby retaining their native structures and functions. The GLPCs preserved their native structures even after 1 year of incubation at ambient temperature. These results provide a framework for the development of protein preservation methods at ambient temperature other than lyophilization.

Optical cryomicroscopy and differential scanning calorimetry of buffer solutions containing cryoprotectants

In the pharmaceutical industry, cryoprotectants are added to buffer formulations to protect the active pharmaceutical ingredient from freeze- and thaw damage. We investigated the freezing and thawing of aqueous sodium citrate buffer with various cryoprotectants, specifically amino acids (cysteine, histidine, arginine, proline and lysine), disaccharides (trehalose and sucrose), polyhydric alcohols (glycerol and mannitol) and surfactants (polysorbate 20 and polysorbate 80). Hereby, we employed optical cryomicroscopy in combination with differential scanning calorimetry in the temperature range to -80 °C. The effect of cryoprotectants on the morphology of the ice crystals, the glass transition temperature and the initial melting temperature is presented. Some of the cryoprotectants have a significant impact on ice crystal size. Disaccharides restrict ice crystal growth, whereas surfactants and glycerol allow ice crystals to increase in size. Cysteine and mannitol cause dehydration after thawing. Either one or two glass transition temperatures were detected, where arginine, surfactants, glycerol, proline and lysine suppress the second, implying a uniform freeze-concentrated solution. The initial melting temperature of pure buffer solution can be shifted up by adding mannitol, both disaccharides and both surfactants; but down by glycerol, proline and lysine.

Ameliorative effects of L-arginine? On heat-induced phase separation of Aristichthys nobilis myosin are associated with the absence of ordered secondary structures of myosin

This investigation aimed to study the potential mechanism of L-arginine (L-Arg) on the heat-induced phase separation phenomenon of myosin from the perspective of conformational changes of myosin. L-Arg ameliorated the phase separation of myosin after a two-step heating procedure via suppression of heat-induced aggregation of myosin. The effect of L-Arg on the heating of myosin at high temperatures (75-85 °C) was more pronounced than that in the setting stage (35-45 °C), suggesting that the ameliorative effects of L-Arg on the heat-induced phase separation of myosin are mainly attributed to the inhibition of rod-rod cross-linking between denatured myosin molecules. Additionally, L-Arg without pH modification exhibited an increased ability to suppress the gelation of myosin compared with pH modification, indicating that both pH effects and the particular structure of L-Arg play noticeable roles in the suppression of myosin gelation. Far-UV circular dichroism, intrinsic fluorescence spectroscopy and differential scanning calorimetry demonstrated that L-Arg induced the absence of ordered secondary structures of myosin molecules, especially β-sheets, and thus generated a looser protein structure, which may represent the dominant suppression mechanisms of L-Arg on the heat-induced aggregation of myosin. This work provided support for the use of L-Arg as a food additive, and the results of this study will be attractive to the meat and beverage products.

Mutational and biophysical robustness in a prestabilized monobody

The fibronectin type III (FN3) monobody domain is a promising non-antibody scaffold, which features a less complex architecture than an antibody while maintaining analogous binding loops. We previously developed FN3Con, a hyperstable monobody derivative with diagnostic and therapeutic potential. Prestabilization of the scaffold mitigates the stability–function trade-off commonly associated with evolving a protein domain toward biological activity. Here, we aimed to examine if the FN3Con monobody could take on antibody-like binding to therapeutic targets, while retaining its extreme stability. We targeted the first of the Adnectin derivative of monobodies to reach clinical trials, which was engineered by directed evolution for binding to the therapeutic target VEGFR2; however, this function was gained at the expense of large losses in thermostability and increased oligomerization. In order to mitigate these losses, we grafted the binding loops from Adnectin-anti-VEGFR2 (CT-322) onto the prestabilized FN3Con scaffold to produce a domain that successfully bound with high affinity to the therapeutic target VEGFR2. This FN3Con-anti-VEGFR2 construct also maintains high thermostability, including remarkable long-term stability, retaining binding activity after 2 years of storage at 36 °C. Further investigations into buffer excipients doubled the presence of monomeric monobody in accelerated stability trials. These data suggest that loop grafting onto a prestabilized scaffold is a viable strategy for the development of monobody domains with desirable biophysical characteristics and that FN3Con is therefore well-suited to applications such as the evolution of multiple paratopes or shelf-stable diagnostics and therapeutics.

Protein Aggregation Inhibitors as Disease-Modifying Therapies for Polyglutamine Diseases

The polyglutamine (polyQ) diseases are a group of inherited neurodegenerative diseases caused by the abnormal expansion of a CAG trinucleotide repeat that are translated into an expanded polyQ stretch in the disease-causative proteins. The expanded polyQ stretch itself plays a critical disease-causative role in the pathomechanisms underlying polyQ diseases. Notably, the expanded polyQ stretch undergoes a conformational transition from the native monomer into the β-sheet-rich monomer, followed by the formation of soluble oligomers and then insoluble aggregates with amyloid fibrillar structures. The intermediate soluble species including the β-sheet-rich monomer and oligomers exhibit substantial neurotoxicity. Therefore, protein conformation stabilization and aggregation inhibition that target the upstream of the insoluble aggregate formation would be a promising approach toward the development of disease-modifying therapies for polyQ diseases. PolyQ aggregation inhibitors of different chemical categories, such as intrabodies, peptides, and small chemical compounds, have been identified through intensive screening methods. Among them, recent advances in the brain delivery methods of several peptides and the screening of small chemical compounds have brought them closer to clinical utility. Notably, the recent discovery of arginine as a potent conformation stabilizer and aggregation inhibitor of polyQ proteins both in vitro and in vivo have paved way to the clinical trial for the patients with polyQ diseases. Meanwhile, expression reduction of expanded polyQ proteins per se would be another promising approach toward disease modification of polyQ diseases. Gene silencing, especially by antisense oligonucleotides (ASOs), have succeeded in reducing the expression of polyQ proteins in the animal models of various polyQ diseases by targeting the aberrant mRNA with expanded CAG repeats. Of note, some of these ASOs have recently been translated into clinical trials. Here we overview and discuss these recent advances toward the development of disease modifying therapies for polyQ diseases. We envision that combination therapies using aggregation inhibitors and gene silencing would meet the needs of the patients with polyQ diseases and their caregivers in the near future to delay or prevent the onset and progression of these currently intractable diseases.

Stacking of nanorings to generate nanotubes for acceleration of protein refolding

Self-assembly and photoisomerization of azobenzene-based amphiphilic molecules produced nanorings with an inner diameter of 25 nm and lengths of <40 nm. The nanorings, which consisted of a single bilayer membrane of the amphiphiles, retained their morphology in the presence of a stacking inhibitor; whereas in the absence of the inhibitor, the nanorings stacked into short nanotubes (<500 nm). When subjected to mild heat treatment, these nanotubes joined end-to-end to form nanotubes with lengths of several tens of micrometers. The nanorings and the short and long nanotubes were able to encapsulate proteins and thereby suppress aggregation induced by thermal denaturation. In addition, the nanotubes accelerated refolding of denatured proteins by encapsulating them and then releasing them into the bulk solution; refolding occurred simultaneously with release. In contrast, the nanorings did not accelerate protein refolding. Refolding efficiency increased with increasing nanotube length, indicating that the re-aggregation of the proteins was strictly inhibited by lowering the concentration of the proteins in the bulk solution as the result of the slow release from the longer nanotubes. The migration of the proteins through the long, narrow nanochannels during the release process will also contribute to refolding.

Arginine is a disease modifier for polyQ disease models that stabilizes polyQ protein conformation

The polyglutamine (polyQ) diseases are a group of inherited neurodegenerative diseases that include Huntington's disease, various spinocerebellar ataxias, spinal and bulbar muscular atrophy, and dentatorubral pallidoluysian atrophy. They are caused by the abnormal expansion of a CAG repeat coding for the polyQ stretch in the causative gene of each disease. The expanded polyQ stretches trigger abnormal β-sheet conformational transition and oligomerization followed by aggregation of the polyQ proteins in the affected neurons, leading to neuronal toxicity and neurodegeneration. Disease-modifying therapies that attenuate both symptoms and molecular pathogenesis of polyQ diseases remain an unmet clinical need. Here we identified arginine, a chemical chaperone that facilitates proper protein folding, as a novel compound that targets the upstream processes of polyQ protein aggregation by stabilizing the polyQ protein conformation. We first screened representative chemical chaperones using an in vitro polyQ aggregation assay, and identified arginine as a potent polyQ aggregation inhibitor. Our in vitro and cellular assays revealed that arginine exerts its anti-aggregation property by inhibiting the toxic β-sheet conformational transition and oligomerization of polyQ proteins before the formation of insoluble aggregates. Arginine exhibited therapeutic effects on neurological symptoms and protein aggregation pathology in Caenorhabditis elegans, Drosophila, and two different mouse models of polyQ diseases. Arginine was also effective in a polyQ mouse model when administered after symptom onset. As arginine has been safely used for urea cycle defects and for mitochondrial myopathy, encephalopathy, lactic acid and stroke syndrome patients, and efficiently crosses the blood-brain barrier, a drug-repositioning approach for arginine would enable prompt clinical application as a promising disease-modifier drug for the polyQ diseases.

Effect of arginine on stability and aggregation of muscle glycogen phosphorylase b

Arginine (Arg) is frequently used in biotechnology and pharmaceutics to stabilize protein preparations. When using charged ions like Arg, it is necessary to take into account their contribution to the increase in ionic strength, in addition to the effect of Arg on particular processes occurring under the conditions of constancy of ionic strength. Here, we examined contribution of ionic strength (0.15 and 0.5 M) to the effects of Arg on denaturation, thermal inactivation and aggregation of skeletal muscle glycogen phosphorylase b (Phb). Dynamic light scattering, analytical ultracentrifugation, differential scanning calorimetry, circular dichroism and enzymatic activity assay were used to assess the effects of Arg at constant ionic strength compared with the effects of ionic strength alone. We found that high ionic strength did not affect the secondary structure of Phb, but changed conformation of the protein. Such a destabilization of the enzyme causes an increase in the initial rate of aggregation and inactivation of Phb thereby affecting its denaturation. Binding of Arg causes additional changes in the protein conformation, weakening the bonds between monomers in the dimer. This causes the dimer to dissociate into monomers, which rapidly aggregate. Thus, Arg acts on these processes much stronger than just ionic strength.

A versatile tool in controlling aggregation and Ag nanoparticles assisted in vitro folding of thermally denatured zDHFR

Background

Proteins have tendency to form inactive aggregates at higher temperatures due to thermal instability. Maintenance of thermal stability is essential to gain the protein in sufficient quantity and biologically active form during their commercial production.

Methods

BL21-DE3 Rosetta E. coli cells which contains plasmid pET43.1a vector was used for producing zDHFR protein commercially. The purification of N-terminal Histidine tagged zDHFR was performed by Immobilized Metal Ion chromatography (IMAC). Investigations were performed in existence and non existence of Silver nanoparticles (AgNPs). The inactivation kinetics of zDHFR in existence and non existence of AgNPs were monitored over a range of 40–80 °C as monitored by UV–Visible absorption spectroscopy.

Results

The protein completely lost its activity at 55 °C. Kinetics of inactivated zDHFR follows first order model in presence and absence of AgNPs. Decrease in rate constant (k) values at respective temperatures depicts that AgNPs contribute in the thermostability of the protein. AgNPs also assists in regaining the activity of zDHFR protein.

Conclusions

AgNPs helps in maintaining thermostability and reducing the aggregation propensity of zDHFR protein.

General significance

Result explains that AgNPs are recommended as a valuable system in enhancing the industrial production of biologically active zDHFR protein which is an important component in folate cycle and essential for survival of cells and prevents the protein from being aggregated.

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Recombinant proteins have the ability to get aggregated during their commercial production due to factors like temperature, pH, etc. Aggregation of protein can be prevented with the help of AgNPs by increasing their thermal stability.

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AgNPs maintain the stability of thermally-denatured zDHFR under high temperatures which is confirmed by kinetic and thermodynamic parameters.

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AgNPs also assists in refolding of the thermally-denatured protein which proves that AgNPs plays a supportive role in maintaining the stability of the protein and thus preventing it from being aggregated.

Protein aggregation as a consequence of non-enzymatic glycation: Therapeutic intervention using aspartic acid and arginine

Non-enzymatic glycation tempted AGEs of proteins are currently at the heart of a number of pathological conditions. Production of chemically stable AGEs can permanently alter the protein structure and function, concomitantly leading to dilapidated situations. Keeping in perspective, present study aims to report the glycation induced structural and functional modification of a cystatin type isolated from rai mustard seeds, using RSC-glucose and RSC-ribose as model system. Among the sugars studied, ribose was found to be most potent glycating agent as evident from different biophysical assays. During the course of incubation, RSC was observed to pass through a series of structural intermediates as revealed by circular dichroism, altered intrinsic fluorescence and high ANS binding. RSC incubation with ribose post day 36 revealed the possible buildup of β structures as observed in CD spectral analysis, hinting towards the generation of aggregated structures in RSC. High thioflavin T fluorescence and increased Congo red absorbance together with enhanced turbidity of the modified form confirmed the aggregation of RSC. The study further revealed anti-glycation and anti-aggregation potential of amino acids; aspartic acid and arginine as they prevented and/or slowed down the process of AGEs and β structure buildup in a concentration dependent manner with arginine proving to be the most effective one.

N-Acetylated-L-arginine (NALA) is an enhanced protein aggregation suppressor under interfacial stresses and elevated temperature for protein liquid formulations

Even though arginine hydrochloride has been recognized as a protein aggregation suppressor in the biopharmaceutical industry, its use has been questioned due to decreasing transition unfolding temperatures (T_m). Four compounds were designed to enhance the role of arginine by changing the length of the carbon chain with removal or N-acetylation of α-amino group. Biophysical properties were observed by differential scanning calorimetry (DSC), dynamic light scattering (DLS), size-exclusion chromatography (SEC), and flow imaging (FI). N-Acetyl-L-arginine (NALA) performed the best at minimizing decrease in T_m with arginine at different pH. NALA also demonstrated relatively higher colloidal stability than arginine hydrochloride, especially in the acidic pH, thereby reducing agitation stress of IgG. Moreover, NALA exhibited a cooperative effect with commercially used glycine buffer for IVIG to maintain the monomer contents with almost no change and suppressed larger particle formation after agitation with heat. The study concludes that the decreasing T_m of proteins by arginine hydrochloride is due to amide group in the α-carbon chain. Moreover, chemical modification on the group compared to removing it will be a breakthrough of arginine's limitations and optimize storage stability of protein therapeutics.

Pyruvate dehydrogenase complex deficiency: updating the clinical, metabolic and mutational landscapes in a cohort of Portuguese patients

BACKGROUND

The pyruvate dehydrogenase complex (PDC) catalyzes the irreversible decarboxylation of pyruvate into acetyl-CoA. PDC deficiency can be caused by alterations in any of the genes encoding its several subunits. The resulting phenotype, though very heterogeneous, mainly affects the central nervous system. The aim of this study is to describe and discuss the clinical, biochemical and genotypic information from thirteen PDC deficient patients, thus seeking to establish possible genotype-phenotype correlations.

RESULTS

The mutational spectrum showed that seven patients carry mutations in the PDHA1 gene encoding the E1α subunit, five patients carry mutations in the PDHX gene encoding the E3 binding protein, and the remaining patient carries mutations in the DLD gene encoding the E3 subunit. These data corroborate earlier reports describing PDHA1 mutations as the predominant cause of PDC deficiency but also reveal a notable prevalence of PDHX mutations among Portuguese patients, most of them carrying what seems to be a private mutation (p.R284X). The biochemical analyses revealed high lactate and pyruvate plasma levels whereas the lactate/pyruvate ratio was below 16; enzymatic activities, when compared to control values, indicated to be independent from the genotype and ranged from 8.5% to 30%, the latter being considered a cut-off value for primary PDC deficiency. Concerning the clinical features, all patients displayed psychomotor retardation/developmental delay, the severity of which seems to correlate with the type and localization of the mutation carried by the patient. The therapeutic options essentially include the administration of a ketogenic diet and supplementation with thiamine, although arginine aspartate intake revealed to be beneficial in some patients. Moreover, in silico analysis of the missense mutations present in this PDC deficient population allowed to envisage the molecular mechanism underlying these pathogenic variants.

CONCLUSION

The identification of the disease-causing mutations, together with the functional and structural characterization of the mutant protein variants, allow to obtain an insight on the severity of the clinical phenotype and the selection of the most appropriate therapy.

Binding of excipients is a poor predictor for aggregation kinetics of biopharmaceutical proteins

One of the major challenges in formulation development of biopharmaceuticals is improving long-term storage stability, which is often achieved by addition of excipients to the final formulation. Finding the optimal excipient for a given protein is usually done using a trial-and-error approach, due to the lack of general understanding of how excipients work for a particular protein. Previously, preferential interactions (binding or exclusion) of excipients with proteins were postulated as a mechanism explaining diversity in the stabilisation effects. Weak preferential binding is however difficult to quantify experimentally, and the question remains whether the formulation process should seek excipients which preferentially bind with proteins, or not. Here, we apply solution NMR spectroscopy to comprehensively evaluate protein-excipient interactions between therapeutically relevant proteins and commonly used excipients. Additionally, we evaluate the effect of excipients on thermal and colloidal protein stability, on aggregation kinetics and protein storage stability at elevated temperatures. We show that there is a weak negative correlation between the strength of protein-excipient interactions and effect on enhancing protein thermal stability. We found that the overall protein-excipient binding per se can be a poor criterion for choosing excipients enhancing formulation stability. Experiments on a diverse set of excipients and test proteins reveal that while excipients affect all of the different aspects of protein stability, the effects are very much protein specific, and care must be taken to avoid apparent generalisations if a smaller dataset is being used.

QTY code designed thermostable and water-soluble chimeric chemokine receptors with tunable ligand affinity

Chemokine receptors are of great interest as they play a critical role in many immunological and pathological processes. The ability to study chemokine receptors in aqueous solution without detergent would be significant because natural receptors require detergents to become soluble. We previously reported using the QTY code to design detergent-free chemokine receptors. We here report the design of 2 detergent-free chimeric chemokine receptors that were experimentally unattainable in detergent solution. We designed chimeric receptors by switching the N terminus and 3 extracellular (EC) loops between different receptors. Specifically, we replaced the N terminus and 3 EC loops of CCR5^QTY with the N terminus and 3 EC loops of CXCR4. The ligand for CXCR4; namely CXCL12, binds to the chimeric receptor CCR5^QTY (7TM)-CXCR4 (N terminus+3 EC loops), but with lower affinity compared to CXCR4; the CCL5 ligand of CCR5 binds the chimeric receptor with ∼20× lower affinity. The chimeric design helps to elucidate the mechanism of native receptor-ligand interaction. We also show that all detergent-free QTY-designed chemokine receptors, expressed in Escherichia coli, bind to their respective chemokines with affinities in the nanomolar (nM) range, similar to the affinities of native receptors and SF9-produced QTY variants. These QTY-designed receptors exhibit remarkable thermostability in the presence of arginine and retain ligand-binding activity after heat treatment at 60 °C for 4 h and 24 h, and at 100 °C for 10 min. Our design approach enables affordable scale-up production of detergent-free QTY variant chemokine receptors with tunable functionality for various uses.

A computational approach to get insights into multiple faces of additives in modulation of protein aggregation pathways

An enormous population worldwide is presently confronted with debilitating neurodegenerative diseases. The etiology of the disease is connected to protein aggregation and the events involved therein. Thus, a complete understanding of an inhibitor at different stages in the process is imperative for the formulation of a drug molecule. This review presents a detailed summary of the current status of different cosolvents. It further develops how the complex aggregation pathway can be simplified into three steps common to all proteins and the way computer simulations can be exploited to gain insights into the ways by which known inhibitors can affect all these stages. Computation of theoretical parameters in this regard and their correlation with experimental techniques is accentuated. In addition to providing an outline of the scope of different additives, this review showcases the way by which the problem of analyzing an effect of an additive can be addressed effectively via MD simulations.

Application of a mixture DOE for the prediction of formulation critical temperatures during lyophilisation process optimisation

During lyophilisation cycle design, primary drying parameters (chamber pressure and shelf temperature) are adjusted to maximize the sublimation rate and prevent cake collapse, by maintaining the product continuously below its critical temperatures. The objective of this study was to employ mixture design of experiments to generate empirical models capable of predicting glass transition of the maximally freeze concentrated solution (Tg') and collapse temperature (Tc) of amorphous protein (BSA and IgG1) formulations. Additionally, the models developed aid the design of high concentration protein formulations with maximised critical temperatures to obtain shorter and more cost-effective lyophilisation cycles. Formulations contain sucrose as cryo/lyo-protectant and arginine/arginine-HCl as multifunctional excipient (e.g. solubility enhancer, viscosity and aggregation suppressor). The impact of formulation components at varied ratios on critical temperatures was evaluated; the amorphous excipients decrease critical temperatures, on the contrary, the protein increases critical temperatures. The robustness of the empirical models generated with BSA formulations was verified with BSA and IgG1 formulations. The models showed greater accuracy in predicting Tg' than the Fox-Flory equation. For the first time, empirical models are reported to predict both critical temperatures. Finally, unconventional collapse events observed for formulations with and without arginine/arginine-HCl at different protein concentrations are also discussed.

Insulin Hot-Spot Analogs Formed with N-Methylated Amino Acid Residues Inhibit Aggregation of Native Hormone

In this study, N-methylated analogs of hot-spots of insulin were designed and synthesized, in the expectation that they would inhibit the aggregation of both insulin hot-spots and the entire hormone. Synthesis of insulin “amyloidogenic” analogs containing N-methylated amino acid residues was performed by microwave-assisted solid phase according to the Fmoc/tert-Bu strategy. As a coupling reagent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate (DMT/NMM/TosO^-) was used. Three independent methods were applied in aggregation studies of the complexes of insulin with its N-methylated peptides. Additionally, circular dichroism (CD) measurements were used to confirm that aggregation processes did not occur in the presence of the N-methylated analogs of hot-spot insulin fragments, and that insulin retains its native conformation. Of the seven N-methylated analogs of the A- and B-chain hot-spots of insulin, six inhibited insulin aggregation (peptides 1 and 3–7). All tested peptides were found to have a lower ability to inhibit the aggregation of insulin hot-spots compared to the capability to inhibit native hormone aggregation.

Counteracting Effect of Charged Amino Acids Against the Destabilization of Proteins by Arginine

Studies on osmolyte-induced effects on proteins help in enhancing protein stability under stressed conditions for various applications. Using mixtures of osmolytes could indeed widen their applications. The combinatorial effects of osmolytes with methylamines are majorly found in the literature; however, such studies are limited on the amino acid class of osmolytes. The present study examines the effect of charged amino acids Arg, Asp, and Lys on the stability of RNase A and α-LA. The thermal stabilities of the proteins in the presence of osmolytes are monitored by absorption changes, and the structural changes are analyzed using fluorescence quenching and near-UV circular dichroism (CD). These results are compared with our previous report on the effect of Glu. Arg destabilizes both the proteins whereas Asp, Lys, and Glu stabilize the proteins. The extent of stability provided by Asp and Glu is almost same and higher than Lys in RNase A. However, the stability acquired in the presence of Asp and Lys is comparable for α-LA and Glu provides higher stability. Further, the quenching and CD results suggest that the addition of amino acids do not alter the structure of the proteins significantly. The counteracting abilities of the stabilizing amino acids (stAAs) against Arg are then investigated. The results show that Glu could counteract Arg at the lowest fraction in the mixture. Lys requires nearly equimolar concentration whereas Asp needs almost double the concentration to counteract Arg induced destabilization of the proteins. At higher concentrations, the counteracting ability of Asp and Lys is similar for both the proteins. The counteracting ratio might slightly vary among the proteins, and it is not necessary that the amino acid providing higher stability to the protein could more effectively counteract Arg. This could be due to the change in the extent of preferential hydration of the proteins by stAAs in the presence of Arg. The results suggest that the addition of stAAs could be an effective strategy to increase the protein stability in biotechnology and biopharma applications.

Complete observation of all structural, conformational, and fibrillation transitions of monomeric globular proteins at submicellar sodium dodecyl sulfate concentrations

Although considerable information is available regarding protein-sodium dodecyl sulfate (SDS) interactions, it is still unclear as to how much SDS is needed to denature proteins. The role of protein charge and micellar surfactant concentration on amyloid fibrillation is also unclear. This study reports on equilibrium measurements of SDS interaction with six model proteins and analyzes the results to obtain a general understanding of conformational breakdown, reorganization and restructuring of secondary structure, and entry into the amyloid fibrillar state. Significantly, all of these responses are entirely resolved at much lower than the critical micellar concentration (CMC) of SDS. Electrostatic interaction of the dodecyl sulfate anion (DS^- ) with positive surface potential on the protein can completely unfold both secondary and tertiary structures, which is followed by protein chain restructuration to α-helices. All SDS-denatured proteins contain more α-helices than the corresponding native state. SDS interaction stochastically drives proteins to the aggregated fibrillar state.