Glycoengineering: the effect of glycosylation on the properties of therapeutic proteins

Identification and quantification of unreported sialylated N-glycan isomers with α2-3 and α2-6 linkages in the egg yolk protein phosvitin

Phosvitin (PV), a highly phosphorylated protein found in chicken egg yolk, possesses multiple bioactivities (including anti-aging and anticancer) and functional properties (including emulsifier and metal-binding capacities). The carbohydrate moiety attached to PV has been reported, but its N-glycan structure is unknown. In this study, we performed structural and quantitative analyses of N-glycans from PV using liquid chromatography-tandem mass spectrometry (MS/MS). N-glycan structures were identified using observed precursor ion m/z and MS/MS fragment ions. Each quantity was obtained relative to the total N-glycans (100%). Thirty-seven N-glycans were identified, including 22 sialylations with a negative charge (a sum of the relative quantity of each, 96.4%) comprising 13 mono- (31.6%), 7 di- (57.5%), 2 tri- (7.3%) sialylations. The sialylated N-glycan isomers with α2-3 (flexible conformation) and α2-6 (rigid conformation) linkages were distinguished using α2-3- and α2-3,6 sialidase treatments and intensity ratios of the N-acetylglucosamine and sialic acid ions (Ln/Nn) with different fragmentation stabilities. The α2-6/α2-6 (53.8%), α2-6 (31.6%), α2-3/α2-6/α2-6 (6.5%), and α2-3/α2-6 (3.7%) linkages in mono-, di, or tri-antennary structures were identified. These negatively charged structures may affect the emulsification and metal-binding capacity of PV. This is the first study to identify and quantify N-glycans in PV, including predominantly 22 sialylated N-glycan isomers with more rigid α2-6 linkages than α2-3 linkages.

Investigation of Protein Therapeutics in Frozen Conditions Using DNP MAS NMR: A Study on Pembrolizumab

The success of modern biopharmaceutical products depends on enhancing the stability of protein therapeutics. Freezing and thawing, which are common thermal stresses encountered throughout the lifecycle of drug substances, spanning protein production, formulation design, manufacturing, storage, and shipping, can impact this stability. Understanding the physicochemical and molecular behaviors of components in biological drug products at temperatures relevant to manufacturing and shipping is essential for assessing stability risks and determining appropriate storage conditions. This study focuses on the stability of high-concentration monoclonal antibody (mAb) pembrolizumab, the drug substance of Keytruda (Merck & Co., Inc., Rahway, NJ, United States), and its excipients in a frozen solution. By leveraging dynamic nuclear polarization (DNP), we achieve more than 100-fold signal enhancements in solid-state NMR (ssNMR), enabling efficient low-temperature (LT) analysis of pembrolizumab without isotopic enrichment. Through both ex situ and in situ ssNMR experiments conducted across a temperature range of 297 to 77 K, we provide insights into the stability of crystalline pembrolizumab under frozen conditions. Importantly, utilizing LT magic-angle spinning (MAS) probes allows us to study molecular dynamics in pembrolizumab from room temperature down to liquid nitrogen temperatures (<100 K). Our results demonstrate that valuable insights into protein conformation and dynamics, crystallinity, and the phase transformations of excipients during the freezing of the formulation matrix can be readily obtained for biological drug products. This study underscores the potential of LT-MAS ssNMR and DNP techniques for analyzing protein therapeutics and vaccines in frozen solutions.

Rapid total sialic acid monitoring during cell culture process using a machine learning model based soft sensor

Total sialic acid content (TSA) in biotherapeutic proteins is often a critical quality attribute as it impacts the drug efficacy. Traditional wet chemical assays to quantify TSA in biotherapeutic proteins during cell culture typically takes several hours or longer due to the complexity of the assay which involves isolation of sialic acid from the protein of interest, followed by sample preparation and chromatographic based separation for analysis. Here, we developed a machine learning model-based technology to rapidly predict TSA during cell culture by using typically measured process parameters. The technology features a user interface, where the users only have to upload cell culture process parameters as input variables and TSA values are instantly displayed on a dashboard platform based on the model predictions. In this study, multiple machine learning algorithms were assessed on our dataset, with the Random Forest model being identified as the most promising model. Feature importance analysis from the Random Forest model revealed that attributes like viable cell density (VCD), glutamate, ammonium, phosphate, and basal medium type are critical for predictions. Notably, while the model demonstrated strong predictability by Day 14 of observation, challenges remain in forecasting TSA values at the edges of the calibration range. This research not only emphasizes the transformative power of machine learning and soft sensors in bioprocessing but also introduces a rapid and efficient tool for sialic acid prediction, signaling significant advancements in bioprocessing. Future endeavors may focus on data augmentation to further enhance model precision and exploration of process control capabilities.

Comprehensive Glycosylation Characterization of Recombinant Human Erythropoietin by Electron-Activated Dissociation Mass Spectrometry

Recombinant human erythropoietin (rhEPO) is a glycoprotein that acts as the main hormone involved in regulating red blood cell production to treat anemia caused by chronic kidney disease or chemotherapy, which has three N-glycosylation sites and one O-glycosylation site. It contains a variety of different glycosylation modifications, such as sialyation, O-acetylation on sialic acids, etc., which causes a big challenge for the glycosylation analysis of rhEPO. In this study, a liquid chromatography-mass spectrometry (LC-MS) method combined with electron-activated dissociation (EAD) technology was used in qualitative and quantitative characterization of rhEPO N-glycosylation and O-glycosylation in just one injection. The usage of EAD not only generated abundant MS/MS fragment ions of glycopeptides and improved the MS/MS sequence coverage but also preserved the glycan structures in the MS/MS fragment ions and the integrity of the glycosidic bond between the glycans and peptides. Three N-glycosylation sites (N24, N38, and N83) and one O-glycosylation site (S126) of rhEPO samples were successfully identified. Among them, the glycosylation ratios of N24, N38, and N83 sites were 82.7%, 100%, and 100% respectively, and 15, 10, and 12 different N-glycans could be identified at the glycopeptide level. The total average number of sialic acids, N-hydroxyacetylneuraminoic acid, and O-acetylation on sialic acid were 7.28, 4.21, and 0.66 at the intact protein level, respectively. For O-glycosylation site S126, O-glycosylation ratios analyzed at the intact protein level and the glycopeptide level were 80.2% and 80.3%, respectively, and two O-glycans were identified, including Core1_S1 and Core1_S2. This study also compared the difference of the glycans and their relative contents in batch-to-batch rhEPO samples. The results proved that the workflow using EAD fragmentation in LC-MS method could be effectively applied for characterizing the glycosylation analysis of rhEPO samples and batch-to-batch consistency analysis, which would help to reasonably guide the optimization of rhEPO production process.

Generalizing a Ligation Site at the N-Glycosylation Sequon for Chemical Synthesis of N-Linked Glycopeptides and Glycoproteins

Chemical synthesis can generate homogeneous glycoproteins with well-defined and modifiable glycan structures at designated sites. The precision and flexibility of the chemical synthetic approach provide a solution to the heterogeneity problem of glycopeptides/glycoproteins obtained through biological approaches. In this study, we reported that the conserved N-glycosylation sequon (Asn-Xaa-Ser/Thr) of glycoproteins can serve as a general site for performing Ser/Thr ligation to achieve N-linked glycoprotein synthesis. We developed an N + 2 strategy to prepare the corresponding glycopeptide salicylaldehyde esters for Ser/Thr ligation and demonstrated that Ser/Thr ligation at the sequon was not affected by the steric hindrance brought about by the large-sized glycan structures. The effectiveness of this strategy was showcased by the total synthesis of the glycosylated receptor-binding domain (RBD) of the SARS-CoV-2 spike protein.

Immobilized enzyme cascade for targeted glycosylation

Glycosylation is a critical post-translational protein modification that affects folding, half-life and functionality. Glycosylation is a non-templated and heterogeneous process because of the promiscuity of the enzymes involved. We describe a platform for sequential glycosylation reactions for tailored sugar structures (SUGAR-TARGET) that allows bespoke, controlled N-linked glycosylation in vitro enabled by immobilized enzymes produced with a one-step immobilization/purification method. We reconstruct a reaction cascade mimicking a glycosylation pathway where promiscuity naturally exists to humanize a range of proteins derived from different cellular systems, yielding near-homogeneous glycoforms. Immobilized β-1,4-galactosyltransferase is used to enhance the galactosylation profile of three IgGs, yielding 80.2-96.3% terminal galactosylation. Enzyme recycling is demonstrated for a reaction time greater than 80 h. The platform is easy to implement, modular and reusable and can therefore produce homogeneous glycan structures derived from various hosts for functional and clinical evaluation.

Development of a biotechnology process for the production of a novel hyperglycosylated long-acting recombinant bovine follicle-stimulating hormone

Follicle-stimulating hormone (FSH) is an important protein used for bovine ovarian hyperstimulation in multiple ovulation and embryo transfer technology (MOET). Several attempts to produce bovine FSH (bFSH) in recombinant systems have been reported, nonetheless, up to date, the most commonly used products are partially purified preparations derived from porcine or ovine (pFSH or oFSH) pituitaries. Here we describe the development of a biotechnology process to produce a novel, hyperglycosylated, long-acting recombinant bFSH (LA-rbFSH) by fusing copies of a highly O-glycosylated peptide. LA-rbFSH and a nonmodified version (rbFSH) were produced in suspension CHO cell cultures and purified by IMAC with high purity levels (>99%). LA-rbFSH presented a higher glycosylation degree and sialic acid content than rbFSH. It also demonstrated a notable improvement in pharmacokinetic properties after administration to rats, including a higher concentration in plasma and a significant (seven-fold) reduction in apparent clearance (CLapp). In addition, the in vivo specific bioactivity of LA-rbFSH in rats was 2.4-fold higher compared to rbFSH. These results postulate this new molecule as an attractive substitute for commercially available porcine pituitary-derived products.

Growing Glycans in Rosetta: Accurate de novo glycan modeling, density fitting, and rational sequon design

Carbohydrates and glycoproteins modulate key biological functions. However, experimental structure determination of sugar polymers is notoriously difficult. Computational approaches can aid in carbohydrate structure prediction, structure determination, and design. In this work, we developed a glycan-modeling algorithm, GlycanTreeModeler, that computationally builds glycans layer-by-layer, using adaptive kernel density estimates (KDE) of common glycan conformations derived from data in the Protein Data Bank (PDB) and from quantum mechanics (QM) calculations. GlycanTreeModeler was benchmarked on a test set of glycan structures of varying lengths, or "trees". Structures predicted by GlycanTreeModeler agreed with native structures at high accuracy for both de novo modeling and experimental density-guided building. We employed these tools to design de novo glycan trees into a protein nanoparticle vaccine to shield regions of the scaffold from antibody recognition, and experimentally verified shielding. This work will inform glycoprotein model prediction, glycan masking, and further aid computational methods in experimental structure determination and refinement.

Enhancing Protein Solubility via Glycosylation: From Chemical Synthesis to Machine Learning Predictions

Glycosylation is a valuable tool for modulating protein solubility; however, the lack of reliable research strategies has impeded efficient progress in understanding and applying this modification. This study aimed to bridge this gap by investigating the solubility of a model glycoprotein molecule, the carbohydrate-binding module (CBM), through a two-stage process. In the first stage, an approach involving chemical synthesis, comparative analysis, and molecular dynamics simulations of a library of glycoforms was employed to elucidate the effect of different glycosylation patterns on solubility and the key factors responsible for the effect. In the second stage, a predictive mathematical formula, innovatively harnessing machine learning algorithms, was derived to relate solubility to the identified key factors and accurately predict the solubility of the newly designed glycoforms. Demonstrating feasibility and effectiveness, this two-stage approach offers a valuable strategy for advancing glycosylation research, especially for the discovery of glycoforms with increased solubility.

What is the role of current mass spectrometry in pharmaceutical analysis?

The role of mass spectrometry (MS) has become more important in most application domains in recent years. Pharmaceutical analysis is specific due to its stringent regulation procedures, the need for good laboratory/manufacturing practices, and a large number of routine quality control analyses to be carried out. The role of MS is, therefore, very different throughout the whole drug development cycle. While it dominates within the drug discovery and development phase, in routine quality control, the role of MS is minor and indispensable only for selected applications. Moreover, its role is very different in the case of analysis of small molecule pharmaceuticals and biopharmaceuticals. Our review explains the role of current MS in the analysis of both small-molecule chemical drugs and biopharmaceuticals. Important features of MS-based technologies being implemented, method requirements, and related challenges are discussed. The differences in analytical procedures for small molecule pharmaceuticals and biopharmaceuticals are pointed out. While a single method or a small set of methods is usually sufficient for quality control in the case of small molecule pharmaceuticals and MS is often not indispensable, a large panel of methods including extensive use of MS must be used for quality control of biopharmaceuticals. Finally, expected development and future trends are outlined.

Effect of Modification Strategies on the Biological Activity of Peptides/Proteins

Covalent attachment of biologically active peptides/proteins with functional moieties is an effective strategy to control their biodistribution, pharmacokinetics, enzymatic digestion, and toxicity. This review focuses on the characteristics of different modification strategies and their effects on the biological activity of peptides/proteins and illustrates their relevant applications and potential.

Towards development of biobetter: L-asparaginase a case study

BACKGROUND

L-asparaginase (ASNase) has played a key role in the management of acute lymphoblastic leukaemia (ALL). As an amidohydrolase, it catalyzes the hydrolysis of L-asparagine, a crucial step in the treatment of ALL. Various ASNase variants have evolved from diverse sources since it was first used in paediatric patients in the 1960s. This review describes the available ASNase and approaches being used to develop ASNase as a biobetter candidate.

SCOPE OF REVIEW

The review discusses the Glycosylation and PEGylation techniques, which are frequently used to develop biobetter versions of the majority of the therapeutic proteins. Further, it explores current ASNase biobetters in therapeutic use and discusses the protein engineering and chemical modification approaches that were employed to reduce immunogenicity, extend protein half-life, and enhance protease stability of ASNase. Emerging strategies like immobilization and encapsulation are also highlighted as potential pathways for improving ASNase properties.

MAJOR CONCLUSIONS

The purpose of the development of ASNase biobetter is to achieve a novel therapeutic candidate that could improve catalytic efficiency, in vivo stability with minimum glutaminase (GLNase) activity and toxicity. Modification of ASNase by immobilization and encapsulation or by fusion technologies like Albumin fusion, Fc fusion, ELP fusion, XTEN fusion, etc. can be exploited to develop a novel biobetter candidate suitable for therapeutic approaches.

GENERAL SIGNIFICANCE

This review emphasizes the importance of biobetter development for therapeutic proteins like ASNase. Improved ASNase molecules have the potential to significantly advance the treatment of ALL and have broader implications in the pharmaceutical industry.

Identification, quantification, and structural role of N-glycans in two highly purified isoforms of sheep testicular hyaluronidase

Animal-derived hyaluronidase, which hydrolyzes the polysaccharide hyaluronic acid, has been used in medical applications despite its limited purity. Additionally, the N-glycan characterization of sheep testicular hyaluronidase (STH) and its structural role remain poorly understood. In this study, STH was purified from the commercially available STH preparation (containing at least 14 impurity proteins) using heparin-affinity chromatography followed by size exclusion chromatography. The structure and quantity of N-glycans of STH were investigated using liquid chromatography-electrospray ionization-high energy collision dissociation-tandem mass spectrometry. Two isoforms, H3S1 and H3S2, of STH were obtained (purity >98 %) with a yield of 3.4 % and 5.1 %, respectively. Fourteen N-glycans, including nine core-fucosylated N-glycans (important for the stability and function of glycoproteins), were identified in both H3S1 and H3S2, with similar quantities of each N-glycan. The amino acid sequences of the proteolytic peptides of H3S1 and H3S2 were compared with those reported in STH. The hyaluronic acid-degrading activity of deglycosylated H3S1 and H3S2 was reduced to 70.8 % and 71.1 % compared to that (100 %) of H3S1 and H3S2, respectively. This is the first report of N-glycan characterization of two highly purified isoforms of STH. These H3S1 and H3S2 will be useful for medical use without unwanted effects of partially purified STH.

Urea-catalyzed N-Glycosylation of Amides/Azacycles with Glycosyl Halides

The efficient synthesis of N-glycosides via direct N-glycosylation of amides/azacycles has been reported. The glycosylation of amides/azacycles with glycosyl halides in the presence of a catalytic amount of urea proceeded smoothly to provide the corresponding N-glycosylated amides or nucleosides in good to excellent yields with 1,2-trans-stereoselectivity. Moreover, by the addition of terpyridine, the 1,2-cis-stereoselectivity was achieved.

Lipidization as a tool toward peptide therapeutics

Peptides, as potential therapeutics continue to gain importance in the search for active substances for the treatment of numerous human diseases, some of which are, to this day, incurable. As potential therapeutic drugs, peptides have many favorable chemical and pharmacological properties, starting with their great diversity, through their high affinity for binding to all sort of natural receptors, and ending with the various pathways of their breakdown, which produces nothing but amino acids that are nontoxic to the body. Despite these and other advantages, however, they also have their pitfalls. One of these disadvantages is the very low stability of natural peptides. They have a short half-life and tend to be cleared from the organism very quickly. Their instability in the gastrointestinal tract, makes it impossible to administer peptidic drugs orally. To achieve the best pharmacologic effect, it is desirable to look for ways of modifying peptides that enable the use of these substances as pharmaceuticals. There are many ways to modify peptides. Herein we summarize the approaches that are currently in use, including lipidization, PEGylation, glycosylation and others, focusing on lipidization. We describe how individual types of lipidization are achieved and describe their advantages and drawbacks. Peptide modifications are performed with the goal of reaching a longer half-life, reducing immunogenicity and improving bioavailability. In the case of neuropeptides, lipidization aids their activity in the central nervous system after the peripheral administration. At the end of our review, we summarize all lipidized peptide-based drugs that are currently on the market.

Engineered therapeutic proteins for sustained-release drug delivery systems

Proteins play a vital role in diverse biological processes in the human body, and protein therapeutics have been applied to treat different diseases such as cancers, genetic disorders, autoimmunity, and inflammation. Protein therapeutics have demonstrated their advantages, such as specific pharmaceutical effects, low toxicity, and strong solubility. However, several disadvantages arise in clinical applications, including short half-life, immunogenicity, and low permeation, leading to reduced drug effectiveness. The structure of protein therapeutics can be modified to increase molecular size, leading to prolonged stability and increased plasma half-life. Notably, the controlled-release delivery systems for the sustained release of protein drugs and preserving the stability of cargo proteins are envisioned as a potential approach to overcome these challenges. In this review, we summarize recent research progress related to structural modifications (PEGylation, glycosylation, poly amino acid modification, and molecular biology-based strategies) and promising long-term delivery systems, such as polymer-based systems (injectable gel/implants, microparticles, nanoparticles, micro/nanogels, functional polymers), lipid-based systems (liposomes, solid lipid nanoparticles, nanostructured lipid carriers), and inorganic nanoparticles exploited for protein therapeutics. STATEMENT OF SIGNIFICANCE: In this review, we highlight recent advances concerning modifying proteins directly to enhance their stability and functionality and discuss state-of-the-art methods for the delivery and controlled long-term release of active protein therapeutics to their target site. In terms of drug modifications, four widely used strategies, including PEGylation, poly amino acid modification, glycosylation, and genetic, are discussed. As for drug delivery systems, we emphasize recent progress relating to polymer-based systems, lipid-based systems developed, and inorganic nanoparticles for protein sustained-release delivery. This review points out the areas requiring focused research attention before the full potential of protein therapeutics for human health and disease can be realized.

Glycosylation shapes the efficacy and safety of diverse protein, gene and cell therapies

Over recent decades, therapeutic proteins have had widespread success in treating a myriad of diseases. Glycosylation, a near universal feature of this class of drugs, is a critical quality attribute that significantly influences the physical properties, safety profile and biological activity of therapeutic proteins. Optimizing protein glycosylation, therefore, offers an important avenue to developing more efficacious therapies. In this review, we discuss specific examples of how variations in glycan structure and glycoengineering impacts the stability, safety, and clinical efficacy of protein-based drugs that are already in the market as well as those that are still in preclinical development. We also highlight the impact of glycosylation on next generation biologics such as T cell-based cancer therapy and gene therapy.

Deglycosylation of eukaryotic-expressed flagellin restores adjuvanticity

Flagellin, the TLR5 agonist, shows potent adjuvant activities in diverse vaccines and immunotherapies. Vibrio vulnificus flagellin B expressed in eukaryotic cells (eFlaB) could not stimulate TLR5 signaling. Enzymatic deglycosylation restored eFlaB's TLR5 stimulating functionality, suggesting that glycosylation interferes with eFlaB binding to TLR5. Site-directed mutagenesis of N-glycosylation residues restored TLR5 stimulation and adjuvanticity. Collectively, deglycosylated eFlaB may provide a built-in adjuvant platform for eukaryotic-expressed antigens and nucleic acid vaccines.

Use of new recombinant proteins for ovarian stimulation in ruminants

Currently, gonadotropin products (follicle stimulating hormone, FSH, and luteinizing hormone, LH) used in animal reproduction are produced by extraction and purification from abattoir-derived pituitary glands. This method, relying on animal-derived materials, carries the potential risk of hormone contamination and pathogen transmission. Additionally, chorionic gonadotropins are extracted from the blood of pregnant mares (equine chorionic gonadotropin; eCG) or the urine of pregnant women (human chorionic gonadotropin; hCG). However, recent advancements have introduced recombinant gonadotropins for assisted animal reproduction therapies. The traditional use of FSH for superovulation has limitations, including labor requirements and variability in superovulation response, affecting the success of in vivo (SOV) and in vitro (OPU/IVEP) embryo production. FSH treatment for superstimulation before OPU can promote the growth of a homogenous follicular population and the recovery of competent oocytes suitable for IVEP procedures. At present, a single injection of a preparation of long-acting bovine recombinant FSH (rFSH) produced similar superovulation responses resulting in the production of good-quality in vivo and in vitro embryos. Furthermore, the treatment with eCG at FTAI protocol has demonstrated its efficacy in promoting follicular growth, ovulation, and P/AI, mainly in heifers and anestrous cows. Currently, treatment with recombinant glycoproteins with eCG-like activity (r-eCG) have shown promising results in increasing follicular growth, ovulation, and P/AI in cows submitted to P4/E2 -based protocols. Bovine somatotropin (bST) is a naturally occurring hormone found in cows. Recombinant bovine somatotropin (rbST), produced through genetic engineering techniques, has shown potential in enhancing reproductive outcomes in ruminants. Treatment with rbST has been found to improve P/IA, increase donor embryo production, and enhance P/ET in recipients. The use of recombinant hormones allows to produce non-animal-derived products, offering several advantages in assisted reproductive technologies for ruminants. This advancement opens up new possibilities for improving reproductive efficiency and success rates in the field of animal reproduction.

Gut microbiome-serum metabolic profiles: insight into the hypoglycemic effect of Porphyra haitanensis glycoprotein on hyperglycemic mice

The hypoglycemic activity of natural algal glycoproteins has attracted interest, but studies of their mechanism of regulating glucose metabolism are lacking. This study investigated the hypoglycemic activity of Porphyra haitanensis glycoprotein (PG) in a mouse hyperglycemia model. The underlying mechanism was elucidated by monitoring changes in the gut microbiome and untargeted serum metabolomics. The results indicated that 30-300 mg kg-1 PG regulated blood glucose levels by increasing insulin secretion, reducing glycated hemoglobin, and improving streptozotocin-induced hyperglycemia in a concentration-dependent manner. In particular, 300 mg kg-1 PG decreased fasting blood glucose by 63.11% and glycosylated hemoglobin by 24.50% and increased insulin secretion by 163.97%. The mechanism of the improvement of hyperglycemia by PG may involve regulating beneficial intestinal bacteria (e.g., norank_f__Muribaculaceae and Lachnospiraceae) and altering the serum metabolic profile (e.g., upregulation of hypotaurine, 3-hydroxy-2-naphthoic acid, and L-glycine), to regulate taurine and hypotaurine, the TCA cycle, AMPK, and pyruvate metabolism. Our findings supported the development of Porphyra haitanensis and its glycoprotein as novel natural antidiabetic compounds to regulate the glycemic balance.

Comparison of Activity and Safety of DSPAα1 and Its N-Glycosylation Mutants

DSPAα1 is a potent rude thrombolytic protein with high medicative value. DSPAα1 has two natural N-glycan sites (N153Q-S154-S155, N398Q-K399-T400) that may lead to immune responses when administered in vivo. We aimed to study the effect of its N-glycosylation sites on DSPAα1 in vitro and in vivo by mutating these N-glycosylation sites. In this experiment, four single mutants and one double mutant were predicted and expressed in Pichia pastoris. When the N398Q-K399-T400 site was mutated, the fibrinolytic activity of the mutant was reduced by 75%. When the N153Q-S154-S155 sites were inactivated as described above, the plasminogen activating activity of its mutant was reduced by 40%, and fibrin selectivity was significantly reduced by 21-fold. The introduction of N-glycosylation on N184-G185-A186T and K368N-S369-S370 also considerably reduced the activity and fibrin selectivity of DSPAα1. The pH tolerance and thermotolerance of all mutants did not change significantly. In vivo experiments also confirmed that N-glycosylation mutations can reduce the safety of DSPAα1, lead to prolonged bleeding time, non-physiological reduction of coagulation factor (α2-AP, PAI) concentration, and increase the risk of irregular bleeding. This study ultimately demonstrated the effect of N-glycosylation mutations on the activity and safety of DSPAα1.

Molecular cloning, characterization and 3D modelling of spotted snakehead fbn1 C-terminal region encoding asprosin and expression analysis of fbn1

The FBN1 gene encodes profibrillin protein that is cleaved by the enzyme furin to release fibrillin-1 and a glucogenic hormone, asprosin. Asprosin is implicated in diverse metabolic functions as well as pathological conditions in mammals. However, till date, there are no studies on asprosin in any non-mammalian vertebrate. In this study, we have retrieved the spotted snakehead Channa punctata fbn1 gene (ss fbn1) from the testicular transcriptome data and validated it. The transcript is predicted to encode 2817 amino acid long putative profibrillin protein. Amino acid sequence alignment of deduced ss profibrillin with human profibrillin revealed that the furin cleavage site in profibrillin is well conserved in C. punctata. Further, differential expression of ss fbn1 was observed in various tissues with the highest expression in gonads. Prominent expression of furin was also observed in the gonads suggesting the possibility of proteolytic cleavage of profibrillin protein and secretion of asprosin in C. punctata. In addition, the C-terminal of the fbn1 gene of C. punctata that codes for asprosin protein has been cloned. Using in silico approach, physicochemical properties of the putative ss asprosin were characterized and post-translational changes were predicted. The putative ss asprosin protein sequence is predicted to consist of 142 amino acid residues, with conserved glycosylation sites. Further, the 3D model of ss asprosin was predicted followed by MD (molecular dynamics) simulation for energy minimization. Thus, the current study, for the first time in non-mammalian vertebrates, predicts and characterizes the novel protein asprosin using in silico approach.

New insight into strategies used to develop long-acting G-CSF biologics for neutropenia therapy

Over the last 20 years, granulocyte colony-stimulating factors (G-CSFs) have become the major therapeutic option for the treatment of patients with neutropenia. Most of the current G-CSFs require daily injections, which are inconvenient and expensive for patients. Increased understanding of G-CSFs' structure, expression, and mechanism of clearance has been very instrumental in the development of new generations of long-acting G-CSFs with improved efficacy. Several approaches to reducing G-CSF clearance via conjugation techniques have been investigated. PEGylation, glycosylation, polysialylation, or conjugation with immunoglobulins or albumins have successfully increased G-CSFs' half-lives. Pegfilgrastim (Neulasta) has been successfully approved and marketed for the treatment of patients with neutropenia. The rapidly expanding market for G-CSFs has increased demand for G-CSF biosimilars. Therefore, the importance of this review is to highlight the principle, elimination's route, half-life, clearance, safety, benefits, and limitations of different strategies and techniques used to increase the half-life of biotherapeutic G-CSFs. Understanding these strategies will allow for a new treatment with more competitive manufacturing and lower unit costs compared with that of Neulasta.

In silico analysis of glycosylation pattern in 5th-6th repeat sequence of reelin glycoprotein

Reelin is an extracellular matrix glycoprotein that plays a key role in cortical development, maturation, synaptic plasticity, and memory formation in the adult mammalian brain. Glycosylation is a significant post- and co-translational modification of proteins. Although glycosylation contributes to the characteristic of proteins from their production to molecular interactions, the knowledge about the glycosylation pattern of reelin is very limited. In this study, we aimed to predict the potential glycosylation pattern of the 5^th-6^th repeat of central reelin fragment that responsible for their signaling, by using in silico methods. We found that the predicted glycosylation pattern of the 5^th-6^th repeat of human reelin was highly conserved between vertebrate species. However, this conservation was not observed in analyzed invertebrates. For the first time, we described the sites of glycosylation at a three-dimensional protein structure in human reelin. Because the sites were very closed to EGF-like repeats and receptor binding sites, they could contribute the interaction with a partner of reelin in addition to the effect of thermostability to protein. Many of the residues related glycosylation were also conserved in analyzed species. These findings may guide biochemical, genetic, and glycobiology base on further experiments about reelin glycosylation. The understanding of reelin glycosylation might change the point of view of treatment for many pathological conditions in neurodegenerative diseases such as Alzheimer's disease. Communicated by Ramaswamy H. Sarma.

Impact of N-Linked Glycosylation on Therapeutic Proteins

Therapeutic proteins have unique advantages over small-molecule drugs in the treatment of various diseases, such as higher target specificity, stronger pharmacological efficacy and relatively low side effects. These advantages make them increasingly valued in drug development and clinical practice. However, although highly valued, the intrinsic limitations in their physical, chemical and pharmacological properties often restrict their wider applications. As one of the most important post-translational modifications, glycosylation has been shown to exert positive effects on many properties of proteins, including molecular stability, and pharmacodynamic and pharmacokinetic characteristics. Glycoengineering, which involves changing the glycosylation patterns of proteins, is therefore expected to be an effective means of overcoming the problems of therapeutic proteins. In this review, we summarize recent efforts and advances in the glycoengineering of erythropoietin and IgG monoclonal antibodies, with the goals of illustrating the importance of this strategy in improving the performance of therapeutic proteins and providing a brief overview of how glycoengineering is applied to protein-based drugs.

Identification of the effect of N-glycan modification and its sialylation on proteolytic stability and glucose-stabilizing activity of glucagon-like peptide 1 by site-directed enzymatic glycosylation

In this study, an approach to prepare long-acting glucagon-like peptide 1 (GLP-1) by site-directed enzymatic glycosylation with homogeneous biantennary complex-type N-glycan has been developed. All the N-glycan-modified GLP-1 analogues preserved an unchanged secondary structure. The glycosylated GLP-1 analogues with sialyl complex-type N-glycan modified at Asn26 and Asn34 exhibited a 36.7- and 24.0-fold in vitro half-life respectively when incubated with dipeptidyl peptidase-IV (DPP-IV), and 25.0- and 13.9-fold respectively when incubated with mouse serum. Compared to native GLP-1, both glycosylated GLP-1 analogues modified at Asn34 by asialyl and sialyl N-glycan demonstrated lower maximum blood glucose levels, as well as more rapid and more persistent glucose-stabilizing capability in type 2 diabetic db/db mice. Our results indicated that the selection of an appropriate position (to avoid hindering the peptide-receptor binding) is crucial for N-glycan modification and its sialylation to improve the therapeutic properties of the modified peptides. The information learned would facilitate future design of therapeutic glycopeptides/glycoproteins with N-glycan to achieve enhanced pharmacological properties.

A universal glycoenzyme biosynthesis pipeline that enables efficient cell-free remodeling of glycans

The ability to reconstitute natural glycosylation pathways or prototype entirely new ones from scratch is hampered by the limited availability of functional glycoenzymes, many of which are membrane proteins that fail to express in heterologous hosts. Here, we describe a strategy for topologically converting membrane-bound glycosyltransferases (GTs) into water soluble biocatalysts, which are expressed at high levels in the cytoplasm of living cells with retention of biological activity. We demonstrate the universality of the approach through facile production of 98 difficult-to-express GTs, predominantly of human origin, across several commonly used expression platforms. Using a subset of these water-soluble enzymes, we perform structural remodeling of both free and protein-linked glycans including those found on the monoclonal antibody therapeutic trastuzumab. Overall, our strategy for rationally redesigning GTs provides an effective and versatile biosynthetic route to large quantities of diverse, enzymatically active GTs, which should find use in structure-function studies as well as in biochemical and biomedical applications involving complex glycomolecules.

Sequential in vitro enzymatic N-glycoprotein modification reveals site-specific rates of glycoenzyme processing

N-glycosylation is an essential eukaryotic posttranslational modification that affects various glycoprotein properties, including folding, solubility, protein–protein interactions, and half-life. N-glycans are processed in the secretory pathway to form varied ensembles of structures, and diversity at a single site on a glycoprotein is termed ‘microheterogeneity’. To understand the factors that influence glycan microheterogeneity, we hypothesized that local steric and electrostatic factors surrounding each site influence glycan availability for enzymatic modification. We tested this hypothesis via expression of reporter N-linked glycoproteins in N-acetylglucosaminyltransferase MGAT1-null HEK293 cells to produce immature Man₅GlcNAc₂ glycoforms (38 glycan sites total). These glycoproteins were then sequentially modified in vitro from high mannose to hybrid and on to biantennary, core-fucosylated, complex structures by a panel of N-glycosylation enzymes, and each reaction time course was quantified by LC-MS/MS. Substantial differences in rates of in vitro enzymatic modification were observed between glycan sites on the same protein, and differences in modification rates varied depending on the glycoenzyme being evaluated. In comparison, proteolytic digestion of the reporters prior to N-glycan processing eliminated differences in in vitro enzymatic modification. Furthermore, comparison of in vitro rates of enzymatic modification with the glycan structures found on the mature reporters expressed in WT cells correlated well with the enzymatic bottlenecks observed in vivo. These data suggest higher order local structures surrounding each glycosylation site contribute to the efficiency of modification both in vitro and in vivo to establish the spectrum of microheterogeneity in N-linked glycoproteins.

Effect of N-glycosylation on secretion, stability, and biological activity of recombinant human interleukin-3 (hIL-3) in Pichia pastoris

Human interleukin-3 (hIL-3) is a clinically important cytokine used to treat hematological malignancies, bone marrow transplantation, cytopenias, and immunological disorders. The cloning of hIL-3 gene was previously reported by our group, where its expression was optimized under methanol-inducible AOX1 promoter having N-terminal α mating factor signal sequence from Saccharomyces cerevisiae. This study investigated the role of glycosylation pattern on its molecular stability, secretion efficiency, and biological activity using the mutagenesis approach. The two N-linked glycosylation positions at N15th (Asn15) and N70th (Asn70) were sequentially mutated to generate three recombinant hIL-3 variants, i.e., N15A, N70A, and N15/70A. Asparagine at these positions was replaced with non-polar alanine amino acid (Ala, A). The alteration of N-linked glycosylation sites was disadvantageous to its efficient secretion in Pichia pastoris, where a 52.32%, 36.48%, 71.41% lower production was observed in N15A, N70A, and N15/70A mutants, respectively, as compared to native control. The fully glycosylated native hIL-3 protein showed higher thermal stability over its deglycosylated counterparts. The biological activity of native, N15A, N70A, and N15/70A hIL-3 protein was evaluated, where N15/70A mutant showed slightly higher proliferation efficacy than other combinations.

Different N-Glycosylation Sites Reduce the Activity of Recombinant DSPAα2

Bat plasminogen activators α2 (DSPAα2) has extremely high medicinal value as a powerful natural thrombolytic protein. However, wild-type DSPAα2 has two N-glycosylation sites (N185 and N398) and its non-human classes of high-mannose-type N-glycans may cause immune responses in vivo. By mutating the N-glycosylation sites, we aimed to study the effect of its N-glycan chain on plasminogen activation, fibrin sensitivity, and to observe the physicochemical properties of DSPAα2. A logical structure design was performed in this study. Four single mutants and one double mutant were constructed and expressed in Pichia pastoris. When the N398 site was eliminated, the plasminogen activator in the mutants had their activities reduced to ~40%. When the N185 site was inactivated, there was a weak decrease in the plasminogen activation of its mutant, while the fibrin sensitivity significantly decreased by ~10-fold. Neither N-glycosylation nor deglycosylation mutations changed the pH resistance or heat resistance of DSPAα2. This study confirms that N-glycosylation affects the biochemical function of DSPAα2, which provides a reference for subsequent applications of DSPAα2.

Association of platelet indices with glycemic status in diabetic dogs

We investigated the platelet count (PLT), mean platelet volume (MPV), and plateletcrit (PCT) in dogs with type 1 diabetes mellitus (DM) compared to healthy controls, and their association with the major fraction of glycated hemoglobin (HbA1c). Blood samples from 33 clinically healthy dogs and 14 newly diagnosed diabetic dogs were included. CBCs were performed with the Advia 120; HbA1c was determined using a validated assay (Capillarys 2 flex-piercing; Sebia). Median [range] PLT and PCT were significantly higher (p = 0.040 and p = 0.010, respectively) in diabetic dogs (434 [176-987] × 10⁹/L and 0.60 [0.26-1.22]%, respectively) compared to healthy dogs (297 [223-671] × 10⁹/L and 0.35 [0.24-0.87]%, respectively]. Thrombocytosis was observed in 6 of 14 (43%) diabetic dogs. The median MPV was not significantly different (p = 0.114) between the diabetic (13.6 fL, 10.1-22.6 fL) and healthy dogs (11.9 fL, 8.6-19.1 fL). A significant, albeit weak, correlation was detected between HbA1c and PLT (rho = 0.298, p = 0.042) and PCT (rho = 0.340, p = 0.019), but no significant correlation was found with MPV (rho = 0.199, p = 0.180). Canine DM was associated with increased PLT and PCT, which was correlated with glycemic status. Our findings suggest dysregulated megakaryopoiesis in diabetic dogs, but this should be confirmed by large-scale studies, and the clinical implications should be investigated.

N-glycosylation, a leading role in viral infection and immunity development

N-linked protein glycosylation is an essential co-and posttranslational protein modification that occurs in all three domains of life; the assembly of N-glycans follows a complex sequence of events spanning the (Endoplasmic Reticulum) ER and the Golgi apparatus. It has a significant impact on both physicochemical properties and biological functions. It plays a significant role in protein folding and quality control, glycoprotein interaction, signal transduction, viral attachment, and immune response to infection. Glycoengineering of protein employed for improving protein properties and plays a vital role in the production of recombinant glycoproteins and struggles to humanize recombinant therapeutic proteins. It considers an alternative platform for biopharmaceuticals production. Many immune proteins and antibodies are glycosylated. Pathogen’s glycoproteins play vital roles during the infection cycle and their expression of specific oligosaccharides via the N-glycosylation pathway to evade detection by the host immune system. This review focuses on the aspects of N-glycosylation processing, glycoengineering approaches, their role in viral attachment, and immune responses to infection.

Assessing detergent-mediated virus inactivation, protein stability, and impurity clearance in biologics downstream processes

Detergent-mediated virus inactivation (VI) provides a valuable orthogonal strategy for viral clearance in mammalian processes, in particular for next-generation continuous manufacturing. Furthermore, there exists an industry-wide need to replace the conventionally employed detergent Triton X-100 with eco-friendly alternatives. However, given Triton X-100 has been the gold standard for VI due its minimal impact on protein stability and high inactivation efficacy, inactivation by other eco-friendly detergents and its impact on protein stability is not well understood. In this study, the sugar-based detergent commonly used in membrane protein purification, n-dodecyl-β- d-maltoside was found to be a promising alternative for VI. We investigated a panel of detergents to compare the relative VI efficacy, impact on therapeutic quality attributes, and clearance of the VI agent and other impurities through subsequent chromatographic steps. Detergent-mediated inactivation and protein stability showed comparable trends to low pH inactivation. Using experimental and modeling data, we found detergent-mediated product aggregation and its kinetics to be driven by extrinsic factors such as detergent and protein concentration. Detergent-mediated aggregation was also impacted by an initial aggregation level as well as intrinsic factors such as the protein sequence and detergent hydrophobicity, and critical micelle concentration. Knowledge gained here on factors driving product stability and VI provides valuable insight to design, standardize, and optimize conditions (concentration and duration of inactivation) for screening of detergent-mediated VI.

Recent Advances Toward Engineering Glycoproteins Using Modified Yeast Display Platforms

Yeast are capable recombinant protein expression hosts that provide eukaryotic posttranslational modifications such as disulfide bond formation and N-glycosylation. This property has been used to create surface display libraries for protein engineering; however, yeast surface display (YSD) with common laboratory strains has limitations in terms of diversifying glycoproteins due to the incorporation of high levels of mannose residues which often obscure important epitopes and are immunogenic in humans. Developing new strains for efficient and appropriate display will require combining existing technologies to permit efficient glycoprotein engineering. Foundational efforts generating knockout strains lacking characteristic hypermannosylation reactions exhibited morphological defects and poor growth. Later strains with "humanized" N-glycosylation machinery surmounted these limitations by targeting a small suite of glycosylhydrolase and glycosyltransferase enzymes from other taxa to the endoplasmic reticulum and Golgi. Advanced yeast strains also provide key modifications at the glycan termini that are essential for the full function of many glycoproteins. Here we review progress toward glycoprotein engineering when glycosylation is required for full function using advanced yeast expression platforms and the suitability of each for YSD of glycoproteins.

Non-human primates in the PKPD evaluation of biologics: Needs and options to reduce, refine, and replace. A BioSafe White Paper

Monoclonal antibodies (mAbs) deliver great benefits to patients with chronic and/or severe diseases thanks to their strong specificity to the therapeutic target. As a result of this specificity, non-human primates (NHP) are often the only preclinical species in which therapeutic antibodies cross-react with the target. Here, we highlight the value and limitations that NHP studies bring to the design of safe and efficient early clinical trials. Indeed, data generated in NHPs are integrated with in vitro information to predict the concentration/effect relationship in human, and therefore the doses to be tested in first-in-human trials. The similarities and differences in the systems defining the pharmacokinetics and pharmacodynamics (PKPD) of mAbs in NHP and human define the nature and the potential of the preclinical investigations performed in NHPs. Examples have been collated where the use of NHP was either pivotal to the design of the first-in-human trial or, inversely, led to the termination of a project prior to clinical development. The potential impact of immunogenicity on the results generated in NHPs is discussed. Strategies to optimize the use of NHPs for PKPD purposes include the addition of PD endpoints in safety assessment studies and the potential re-use of NHPs after non-terminal studies or cassette dosing several therapeutic agents of interest. Efforts are also made to reduce the use of NHPs in the industry through the use of in vitro systems, alternative in vivo models, and in silico approaches. In the case of prediction of ocular PK, the body of evidence gathered over the last two decades renders the use of NHPs obsolete. Expert perspectives, advantages, and pitfalls with these alternative approaches are shared in this review.

Building better biobetters: From fundamentals to industrial application

Biological drugs or biopharmaceuticals off patent open a large market for biosimilars and biobetters, follow-on biologics. Biobetters, in particular, are new drugs designed from existing ones with improved properties such as higher selectivity, stability, half-life and/or lower toxicity/immunogenicity. Glycosylation is one of the most used strategies to improve biological drugs, nonetheless bioconjugation is an additional alternative and refers to the covalent attachment of polymers to biological drugs. Extensive research on novel polymers is underway, nonetheless PEGylation is still the best alternative with the longest clinical track record. Innovative trends based on genetic engineering techniques such as fusion proteins and PASylation are also promising. In this review, all these alternatives wereexplored as well as current market trends, legislation and future perspectives.

Glycosylation decreases aggregation and immunogenicity of adalimumab Fab secreted from Pichia pastoris

Glycoengineering of therapeutic proteins has been applied to improve the clinical efficacy of several therapeutics. Here, we examined the effect of glycosylation on the properties of the Fab of the therapeutic antibody, adalimumab. An N-glycosylation site was introduced at position 178 of the H chain constant region of adalimumab Fab through site-directed mutagenesis (H:L178N Fab), and the H:L178N Fab was produced in Pichia pastoris. Expressed mutant Fab contained long and short glycan chains (L-glyco Fab and S-glyco Fab, respectively). Under the condition of aggregation of Fab upon pH shift-induced stress, both of L-glyco Fab and S-glyco Fab were less prone to aggregation, with L-glyco Fab suppressing aggregation more effectively than the S-glyco Fab. Moreover, the comparison of the antigenicity of glycosylated and wild-type Fabs in mice revealed that glycosylation resulted in the suppression of antigenicity. Analysis of the pharmacokinetic behaviour of the Fab, L-glyco Fab and S-glyco Fab indicated that the half-lives of glycosylated Fabs in the rats were shorter than that of wild-type Fab, with L-glyco Fab having a shorter half-life than S-glyco Fab. Thus, we demonstrated that the glycan chain influences Fab aggregation and immunogenicity, and glycosylation reduces the elimination half-life in vivo.

Glucose-Lipopeptide Conjugates Reveal the Role of Glucose Modification Position in Complexation and the Potential of Malignant Melanoma Therapy

Glycosylation and fatty acid modification are promising strategies to improve peptide performance. We previously studied glycosylation and fatty acid modification of the anticancer peptide R-lycosin-I. In this study, we further investigated the co-modification of fatty acids and monosaccharides in R-lycosin-I. A glucose derivative was covalently coupled to the ε-amino group of the Lys residues of the lipopeptide R-C₁₂, which was derived from R-lycosin-I modified with dodecanoic acid, and obtained seven glycolipid peptides. They exhibited different cytotoxicity profiles, which may be related to the changes in physicochemical properties and binding ability to glucose transporter 1 (GLUT1). Among them, R-C₁₂-4 exhibited the highest cytotoxicity and improved selectivity. A further study demonstrated that R-C₁₂-4 showed significant cytotoxicity and antimetastasis activity in murine melanoma cells, melanoma spheroids, and animal models. Our results indicated that the glucose derivative modification position plays important roles in glucose-lipopeptide conjugates, and R-C₁₂-4 might be a promising lead for developing anticancer drugs.

Engineered Fc-glycosylation switch to eliminate antibody effector function

Antibodies mediate effector functions through Fcγ receptor (FcγR) interactions and complement activation, causing cytokine release, degranulation, phagocytosis, and cell death. They are often undesired for development of therapeutic antibodies where only antigen binding or neutralization would be ideal. Effector elimination has been successful with extensive mutagenesis, but these approaches can potentially lead to manufacturability and immunogenicity issues. By switching the native glycosylation site from position 297 to 298, we created alternative antibody glycosylation variants in the receptor interaction interface as a novel strategy to eliminate the effector functions. The engineered glycosylation site at Asn298 was confirmed by SDS-PAGE, mass spectrometry, and X-ray crystallography (PDB code 6X3I). The lead NNAS mutant (S298N/T299A/Y300S) shows no detectable binding to mouse or human FcγRs by surface plasmon resonance analyses. The effector functions of the mutant are completely eliminated when measured in antibody-dependent cell-meditated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays. In vivo, the NNAS mutant made on an antibody against a human lymphocyte antigen does not deplete T cells or B cells in transgenic mice, in contrast to wild-type antibody. Structural study confirms the successful glycosylation switch to the engineered Asn298 site. The engineered glycosylation would clash with approaching FcγRs based on reported Fc-FcγR co-crystal structures. In addition, the NNAS mutants of multiple antibodies retain binding to antigens and neonatal Fc receptor, exhibit comparable purification yields and thermal stability, and display normal circulation half-life in mice and non-human primate. Our work provides a novel approach for generating therapeutic antibodies devoid of any ADCC and CDC activities with potentially lower immunogenicity.

An integrated modular framework for modeling the effect of ammonium on the sialylation process of monoclonal antibodies produced by CHO cells

BACKGROUND

Monoclonal antibodies (mABs) have emerged as one of the most important therapeutic recombinant proteins in the pharmaceutical industry. Their immunogenicity and therapeutic efficacy are influenced by post-translational modifications, specifically the glycosylation process. Bioprocess conditions can influence the intracellular process of glycosylation. Among all the process conditions that have been recognized to affect the mAB glycoforms, the detailed mechanism underlying how ammonium could perturb glycosylation remains to be fully understood. It was shown that ammonium induces heterogeneity in protein glycosylation by altering the sialic acid content of glycoproteins. Hence, understanding this mechanism would aid pharmaceutical manufacturers to ensure consistent protein glycosylation.

METHODS

Three different mechanisms have been proposed to explain how ammonium influences the sialylation process. In the first, the inhibition of CMP-sialic acid transporter, which transports CMP-sialic acid (sialylation substrate) into the Golgi, by an increase in UDP-GlcNAc content that is brought about by the augmented incorporation of ammonium into glucosamine formation. In the second, ammonia diffuses into the Golgi and raises its pH, thereby decreasing the sialyltransferase enzyme activity. In the third, the reduction of sialyltransferase enzyme expression level in the presence of ammonium. We employed these mechanisms in a novel integrated modular platform to link dynamic alteration in mAB sialylation process with extracellular ammonium concentration to elucidate how ammonium alters the sialic acid content of glycoproteins.

RESULTS

Our results show that the sialylation reaction rate is insensitive to the first mechanism. At low ammonium concentration, the second mechanism is the controlling mechanism in mAB sialylation and by increasing the ammonium level (< 8 mM) the third mechanism becomes the controlling mechanism. At higher ammonium concentrations (> 8 mM) the second mechanism becomes predominant again.

CONCLUSION

The presented model in this study provides a connection between extracellular ammonium and the monoclonal antibody sialylation process. This computational tool could help scientists to develop and formulate cell culture media. The model illustrated here can assist the researchers to select culture media that ensure consistent mAB sialylation.

Customized yeast cell factories for biopharmaceuticals: from cell engineering to process scale up

The manufacture of recombinant therapeutics is a fastest-developing section of therapeutic pharmaceuticals and presently plays a significant role in disease management. Yeasts are established eukaryotic host for heterologous protein production and offer distinctive benefits in synthesising pharmaceutical recombinants. Yeasts are proficient of vigorous growth on inexpensive media, easy for gene manipulations, and are capable of adding post translational changes of eukaryotes. Saccharomyces cerevisiae is model yeast that has been applied as a main host for the manufacture of pharmaceuticals and is the major tool box for genetic studies; nevertheless, numerous other yeasts comprising Pichia pastoris, Kluyveromyces lactis, Hansenula polymorpha, and Yarrowia lipolytica have attained huge attention as non-conventional partners intended for the industrial manufacture of heterologous proteins. Here we review the advances in yeast gene manipulation tools and techniques for heterologous pharmaceutical protein synthesis. Application of secretory pathway engineering, glycosylation engineering strategies and fermentation scale-up strategies in customizing yeast cells for the synthesis of therapeutic proteins has been meticulously described.

Glycoprotein Semisynthesis by Chemical Insertion of Glycosyl Asparagine Using a Bifunctional Thioacid-Mediated Strategy

Glycosylation is a major modification of secreted and cell surface proteins, and the resultant glycans show considerable heterogeneity in their structures. To understand the biological processes arising from each glycoform, the preparation of homogeneous glycoproteins is essential for extensive biological experiments. To establish a more robust and rapid synthetic route for the synthesis of homogeneous glycoproteins, we studied several key reactions based on amino thioacids. We found that diacyl disulfide coupling (DDC) formed with glycosyl asparagine thioacid and peptide thioacid yielded glycopeptides. This efficient coupling reaction enabled us to develop a new glycoprotein synthesis method, such as the bifunctional thioacid-mediated strategy, which can couple two peptides with the N- and C-termini of glycosyl asparagine thioacid. Previous glycoprotein synthesis methods required valuable glycosyl asparagine in the early stage and subsequent multiple glycoprotein synthesis routes, whereas the developed concept can generate glycoproteins within a few steps from peptide and glycosyl asparagine thioacid. Herein, we report the characterization of the DDC of amino thioacids and the efficient ability of glycosyl asparagine thioacid to be used for robust glycoprotein semisynthesis.

Identification and Relative Quantification of hFSH Glycoforms in Women's Sera via MS-PRM-Based Approach

Follicle-stimulating hormone (FSH) is a glycohormone synthesized by adenohypophysis, and it stimulates ovulation in women and spermatogenesis in men by binding to its receptor (FSHR). FSHR is involved in several mechanisms to transduce intracellular signals in response to the FSH stimulus. Exogenous FSH is currently used in the clinic for ovarian hyperstimulation during in vitro fertilization in women, and for treatment of infertility caused by gonadotropin deficiency in men. The glycosylation of FSH strongly affects the binding affinity to its receptor, hence significantly influencing the biological activity of the hormone. Therefore, the accurate measurement and characterization of serum hFSH glycoforms will contribute to elucidating the complex mechanism of action by which different glycoforms elicit distinct biological activity. Nowadays ELISA is the official method with which to monitor serum hFSH, but the test is unable to distinguish between the different FSH glycovariants and is therefore unsuitable to study the biological activity of this hormone. This study presents a preliminary alternative strategy for identifying and quantifying serum hFSH glycoforms based on immunopurification assay and mass spectrometry (MS), and parallel reaction monitoring (PRM) analysis. In this study, we provide an MS–PRM data acquisition method for hFSH glycopeptides identification with high specificity and their quantification by extracting the chromatographic traces of selected fragments of glycopeptides. Once set up for all its features, the proposed method could be transferred to the clinic to improve fertility treatments and follow-ups in men and women.

Exploring the Role of Glycans in the Interaction of SARS-CoV-2 RBD and Human Receptor ACE2

COVID-19 is a highly infectious respiratory disease caused by the novel coronavirus SARS-CoV-2. It has become a global pandemic and its frequent mutations may pose new challenges for vaccine design. During viral infection, the Spike RBD of SARS-CoV-2 binds the human host cell receptor ACE2, enabling the virus to enter the host cell. Both the Spike and ACE2 are densely glycosylated, and it is unclear how distinctive glycan types may modulate the interaction of RBD and ACE2. Detailed understanding of these determinants is key for the development of novel therapeutic strategies. To this end, we perform extensive all-atom simulations of the (i) RBD-ACE2 complex without glycans, (ii) RBD-ACE2 with oligomannose MAN9 glycans in ACE2, and (iii) RBD-ACE2 with complex FA2 glycans in ACE2. These simulations identify the key residues at the RBD-ACE2 interface that form contacts with higher probabilities, thus providing a quantitative evaluation that complements recent structural studies. Notably, we find that this RBD-ACE2 contact signature is not altered by the presence of different glycoforms, suggesting that RBD-ACE2 interaction is robust. Applying our simulated results, we illustrate how the recently prevalent N501Y mutation may alter specific interactions with host ACE2 that facilitate the virus-host binding. Furthermore, our simulations reveal how the glycan on Asn90 of ACE2 can play a distinct role in the binding and unbinding of RBD. Finally, an energetics analysis shows that MAN9 glycans on ACE2 decrease RBD-ACE2 affinity, while FA2 glycans lead to enhanced binding of the complex. Together, our results provide a more comprehensive picture of the detailed interplay between virus and human receptor, which is much needed for the discovery of effective treatments that aim at modulating the physical-chemical properties of this virus.

Rational design of hyper-glycosylated human follicle-stimulating hormone analogs (a bioinformatics approach)

N-glycosylation is a complex mechanism in which the carbohydrate molecules bind to the Asn amino acid in the N-glycan consensus sequence (AsnXxxThr/Ser sequon, where Xxx is any residue, excluding Pro). Introduction of additional N-linked glycosylation site into proposed location in the protein causes to its hyper-glycosylation and can enhance the protein characteristics to provide promising prospects in treatment. Glycoengineering is a favorably used strategy to design and generate hyper-glycosylated variants. In this research, human follicle-stimulating hormone (HuFSH) was considered to identify appropriate positions for adding novel N-glycan sites. A rational computational strategy was applied to predict functional/structural variations induced through changes in polypeptide chain. We analyzed the amino acid chain of FSH to find out the proper locations to introduce asparagine and/or threonine for creating novel N-glycan positions. This analysis resulted in the recognition of 40 possible N-glycosylation positions, and then the eight adequate ones were chosen for additional investigation. The model validation techniques were used to examine 3-dimensional structures of the chosen mutant proteins. Finally, 2 mutants with a further glycan site were recommended as eligible FSH hyper-glycosylated analogs, which may be regarded for subsequent experimental studies. Our in silico approach may decrease tedious and time-wasting laboratory researches of the mutants.Communicated by Ramaswamy H. Sharma.

Process intensification to produce a difficult-to-express therapeutic enzyme by high cell density perfusion or enhanced fed-batch

Intensified bioprocesses have caught industrial interest in the field of biomanufacturing in recent years. Thanks to new technology, intensified processes can support high cell densities, higher productivities and longer process times, which together can offer lower cost of goods. In this study two different intensified process modes, high cell density perfusion and enhanced fed-batch, were evaluated and compared with a conventional fed-batch process for a difficult-to-express therapeutic enzyme. The intensified process modes were cultivated with a target cell density of 100 × 10⁶  cells/ml and with alternating tangential flow filtration, ATF, as cell retention device. The processes were designed to resemble an established optimized fed-batch process using the knowledge of this process without new dedicated optimization for the intensified modes. The design strategy included decision of the ratio of feed concentrate to base medium and glucose supplementation, which were based on target cell-specific consumption rates of key amino acids and glucose, using a targeted feeding approach (TAFE). A difficult-to-express therapeutic enzyme with multiple glycosylation sites was expressed and analyzed in the different production processes. The two new intensified processes both achieved 10 times higher volumetric productivity (mg/L/day) with retained protein quality and minor changes to the glycan profile compared to the fed-batch process. The study demonstrates the potential of using intensified processes for sensitive complex enzymes. It is shown here that it is possible to transfer a developed fed-batch process into high cell density processes either in intensified fed-batch or steady-state perfusion without new dedicated optimization. The results demonstrated as well that these intensified modes significantly increase the productivity while maintaining the desired product quality, for instance the same amount of product was obtained in 1 day during the perfusion process than in a whole fed-batch run. Without any prior optimization of the perfusion rate, the high cell density perfusion process resulted in only 1.2 times higher medium cost per gram produced protein.

Chemical (neo)glycosylation of biological drugs

Biological drugs, specifically proteins and peptides, are a privileged class of medicinal agents and are characterized with high specificity and high potency of therapeutic activity. However, biologics are fragile and require special care during storage, and are often modified to optimize their pharmacokinetics in terms of proteolytic stability and blood residence half-life. In this review, we showcase glycosylation as a method to optimize biologics for storage and application. Specifically, we focus on chemical glycosylation as an approach to modify biological drugs. We present case studies that illustrate the success of this methodology and specifically address the highly important question: does connectivity within the glycoconjugate have to be native or not? We then present the innovative methods of chemical glycosylation of biologics and specifically highlight the emerging and established protecting group-free methodologies of glycosylation. We discuss thermodynamic origins of protein stabilization via glycosylation, and analyze in detail stabilization in terms of proteolytic stability, aggregation upon storage and/or heat treatment. Finally, we present a case study of protein modification using sialic acid-containing glycans to avoid hepatic clearance of biological drugs. This review aims to spur interest in chemical glycosylation as a facile, powerful tool to optimize proteins and peptides as medicinal agents.

Recombinant human lactoferrin carrying humanized glycosylation exhibits antileukemia selective cytotoxicity, microfilament disruption, cell cycle arrest, and apoptosis activities

Lactoferrin has gained extensive attention due to its ample biological properties. In this study, recombinant human lactoferrin carrying humanized glycosylation (rhLf-h-glycan) expressed in the yeast Pichia pastoris SuperMan5, which is genetically glycoengineered to efficiently produce functional humanized glycoproteins inclosing (Man)5(GlcNAc)2 Asn-linked glycans, was analyzed, inspecting its potential toxicity against cancer cells. The live-cell differential nuclear staining assay was used to quantify the rhLf-h-glycan cytotoxicity, which was examined in four human cell lines: acute lymphoblastic leukemia (ALL) CCRF-CEM, T-cell lymphoblastic lymphoma SUP-T1, cervical adenocarcinoma HeLa, and as control, non-cancerous Hs27 cells. The defined CC50 values of rhLf-h-glycan in CCRF-CEM, SUP-T1, HeLa, and Hs27 cells were 144.45 ± 4.44, 548.47 ± 64.41, 350 ± 14.82, and 3359.07 ± 164 µg/mL, respectively. The rhLf-h-glycan exhibited a favorable selective cytotoxicity index (SCI), preferentially killing cancer cells: 23.25 for CCRF-CEM, 9.59 for HeLa, and 6.12 for SUP-T1, as compared with Hs27 cells. Also, rhLf-h-glycan showed significant antiproliferative activity (P < 0.0001) at 24, 48, and 72 h of incubation on CCRF-CEM cells. Additionally, it was observed via fluorescent staining and confocal microscopy that rhLf-h-glycan elicited apoptosis-associated morphological changes, such as blebbing, nuclear fragmentation, chromatin condensation, and apoptotic bodies in ALL cells. Furthermore, rhLf-h-glycan-treated HeLa cells revealed shrinkage of the microfilament structures, generating a speckled/punctuated pattern and also caused PARP-1 cleavage, a hallmark of apoptosis. Moreover, in ALL cells, rhLf-h-glycan altered cell cycle progression inducing the G2/M phase arrest, and caused apoptotic DNA fragmentation. Overall, our findings revealed that rhLf-h-glycan has potential as an anticancer agent and therefore deserves further in vivo evaluation.