Challenges in therapeutic glycoprotein production

In-Membrane Enrichment and Peptic Digestion to Facilitate Analysis of Monoclonal Antibody Glycosylation

The number of therapeutic monoclonal antibodies (mAbs) is growing rapidly due to their widespread use for treating various diseases and health conditions. Assessing the glycosylation profile of mAbs during production is essential to ensuring their safety and efficacy. This research aims to rapidly isolate and digest mAbs for liquid chromatography-tandem mass spectrometry (LC-MS/MS) identification of glycans and monitoring of glycosylation patterns, potentially during manufacturing. Immobilization of an Fc region-specific ligand, oFc20, in a porous membrane enables the enrichment of mAbs from cell culture supernatant and efficient elution with an acidic solution. Subsequent digestion of the mAb eluate occurred in a pepsin-modified membrane within 5 min. The procedure does not require alkylation and desalting, greatly shortening the sample preparation time. Subsequent LC-MS/MS analysis identified 11 major mAb N-glycan proteoforms and assessed the relative peak areas of the glycosylated peptides. This approach is suitable for the glycosylation profiling of various human IgG mAbs, including biosimilars and different IgG subclasses. The total time required for this workflow is less than 2 h, whereas the conventional enzymatic release and labeling of glycans can take much longer. Thus, the integrated membranes are suitable for facilitating the analysis of mAb glycosylation patterns.

Using High-Throughput Experiments To Screen N-Glycosyltransferases with Altered Specificities

The important roles that protein glycosylation plays in modulating the activities and efficacies of protein therapeutics have motivated the development of synthetic glycosylation systems in living bacteria and in vitro. A key challenge is the lack of glycosyltransferases that can efficiently and site-specifically glycosylate desired target proteins without the need to alter primary amino acid sequences at the acceptor site. Here, we report an efficient and systematic method to screen a library of glycosyltransferases capable of modifying comprehensive sets of acceptor peptide sequences in parallel. This approach is enabled by cell-free protein synthesis and mass spectrometry of self-assembled monolayers and is used to engineer a recently discovered prokaryotic N-glycosyltransferase (NGT). We screened 26 pools of site-saturated NGT libraries to identify relevant residues that determine polypeptide specificity and then characterized 122 NGT mutants, using 1052 unique peptides and 52,894 unique reaction conditions. We define a panel of 14 NGTs that can modify 93% of all sequences within the canonical X-1-N-X+1-S/T eukaryotic glycosylation sequences as well as another panel for many noncanonical sequences (with 10 of 17 non-S/T amino acids at the X+2 position). We then successfully applied our panel of NGTs to increase the efficiency of glycosylation for three protein therapeutics. Our work promises to significantly expand the substrates amenable to in vitro and bacterial glycoengineering.

Comparative transport analysis of cell penetrating peptides and Lysosomal sequences for selective tropism towards RPE cells

Cell penetrating peptides are typically nonspecific, targeting multiple cell types without discrimination. However, subsets of Cell penetrating peptides (CPP) have been found, which show a 'homing' capacity or increased likelihood of internalizing into specific cell types and subcellular locations. Therapeutics intended to be delivered to tissues with a high degree of cellular diversity, such as the intraocular space, would benefit from delivery using CPP that can discriminate across multiple cell types. Lysosomal storage diseases in the retinal pigment epithelium (RPE) can impair cargo clearance, leading to RPE atrophy and blindness. Characterizing CPP for their capacity to effectively deliver cargo to the lysosomes of different cell types may expand treatment options for lysosomal storage disorders. We developed a combinatorial library of CPP and lysosomal sorting signals, applied to ARPE19 and B3 corneal lens cells, for the purpose of determining cell line specificity and internal targeting. Several candidate classes of CPP were found to have as much as 4 times the internalization efficiency in ARPE19 compared to B3. Follow-up cargo transport studies were also performed, which demonstrate effective internalization and lysosomal targeting in ARPE19 cells.

Simplifying glycan monitoring of complex antigens such as the SARS-CoV-2 spike to accelerate vaccine development

Glycosylation is a key quality attribute that must be closely monitored for protein therapeutics. Established assays such as HILIC-Fld of released glycans and LC-MS of glycopeptides work well for glycoproteins with a few glycosylation sites but are less amenable for those with multiple glycosylation sites, resulting in complex datasets that are time consuming to generate and difficult to analyze. As part of efforts to improve preparedness for future pandemics, researchers are currently assessing where time can be saved in the vaccine development and production process. In this context, we evaluated if neutral and acidic monosaccharides analysis via HPAEC-PAD could be used as a rapid and robust alternative to LC-MS and HILIC-Fld for monitoring glycosylation between protein production batches. Using glycoengineered spike proteins we show that the HPAEC-PAD monosaccharide assays could quickly and reproducibly detect both major and minor glycosylation differences between batches. Moreover, the monosaccharide results aligned well with those obtained by HILIC-Fld and LC-MS.

Rapid biosynthesis of glycoprotein therapeutics and vaccines from freeze-dried bacterial cell lysates

The advent of distributed biomanufacturing platforms promises to increase agility in biologic production and expand access by reducing reliance on refrigerated supply chains. However, such platforms are not capable of robustly producing glycoproteins, which represent the majority of biologics approved or in development. To address this limitation, we developed cell-free technologies that enable rapid, modular production of glycoprotein therapeutics and vaccines from freeze-dried Escherichia coli cell lysates. Here, we describe a protocol for generation of cell-free lysates and freeze-dried reactions for on-demand synthesis of desired glycoproteins. The protocol includes construction and culture of the bacterial chassis strain, cell-free lysate production, assembly of freeze-dried reactions, cell-free glycoprotein synthesis, and glycoprotein characterization, all of which can be completed in one week or less. We anticipate that cell-free technologies, along with this comprehensive user manual, will help accelerate development and distribution of glycoprotein therapeutics and vaccines.

Improving recombinant protein production in CHO cells using the CRISPR-Cas system

Chinese hamster ovary (CHO) cells are among the most widely used mammalian cell lines in the biopharmaceutical industry. Therefore, it is not surprising that significant efforts have been made around the engineering of CHO cells using genetic engineering methods such as the CRISPR-Cas system. In this review, we summarize key recent studies that have used different CRISPR-Cas systems such as Cas9, Cas13 or dCas9 fused with effector domains to improve recombinant protein (r-protein) production in CHO cells. Here, every relevant stage of production was considered, underscoring the advantages and limitations of these systems, as well as discussing their bottlenecks and probable solutions. A special emphasis was given on how these systems could disrupt and/or regulate genes related to glycan composition, which has relevant effects over r-protein properties and in vivo activity. Furthermore, the related promising future applications of CRISPR to achieve a tunable, reversible, or highly stable editing of CHO cells are discussed. Overall, the studies covered in this review show that despite the complexity of mammalian cells, the synthetic biology community has developed many mature strategies to improve r-protein production using CHO cells. In this regard, CRISPR-Cas technology clearly provides efficient and flexible genetic manipulation and allows for the generation of more productive CHO cell lines, leading to more cost-efficient production of biopharmaceuticals, however, there is still a need for many emerging techniques in CRISPR to be reported in CHO cells; therefore, more research in these cells is needed to realize the full potential of this technology.

Optimising expression and extraction of recombinant proteins in plants

Recombinant proteins are of paramount importance for research, industrial and medical use. Numerous expression chassis are available for recombinant protein production, and while bacterial and mammalian cell cultures are the most widely used, recent developments have positioned transgenic plant chassis as viable and often preferential options. Plant chassis are easily maintained at low cost, are hugely scalable, and capable of producing large quantities of protein bearing complex post-translational modification. Several protein targets, including antibodies and vaccines against human disease, have been successfully produced in plants, highlighting the significant potential of plant chassis. The aim of this review is to act as a guide to producing recombinant protein in plants, discussing recent progress in the field and summarising the factors that must be considered when utilising plants as recombinant protein expression systems, with a focus on optimising recombinant protein expression at the genetic level, and the subsequent extraction and purification of target proteins, which can lead to substantial improvements in protein stability, yield and purity.

Engineering Self-Assembling Protein Nanoparticles for Therapeutic Delivery

Despite remarkable advances over the past several decades, many therapeutic nanomaterials fail to overcome major in vivo delivery barriers. Controlling immunogenicity, optimizing biodistribution, and engineering environmental responsiveness are key outstanding delivery problems for most nanotherapeutics. However, notable exceptions exist including some lipid and polymeric nanoparticles, some virus-based nanoparticles, and nanoparticle vaccines where immunogenicity is desired. Self-assembling protein nanoparticles offer a powerful blend of modularity and precise designability to the field, and have the potential to solve many of the major barriers to delivery. In this review, we provide a brief overview of key designable features of protein nanoparticles and their implications for therapeutic delivery applications. We anticipate that protein nanoparticles will rapidly grow in their prevalence and impact as clinically relevant delivery platforms.

Accelerating therapeutic protein design

Protein structures provide for defined microenvironments that can support complex pharmacological functions, otherwise unachievable by small molecules. The advent of therapeutic proteins has thus greatly broadened the range of manageable disorders. Leveraging the knowledge and recent advances in de novo protein design methods has the prospect of revolutionizing how protein drugs are discovered and developed. This review lays out the main challenges facing therapeutic proteins discovery and development, and how present and future advancements of protein design can accelerate the protein drug pipelines.

Analysis of N-glycan profile of Arabidopsis alg3 cell culture

N-Glycosylation is essential for protein stability, activity and characteristics, and is often needed to deliver pharmaceutical glycoproteins to target cells. A paucimannosidic structure, Man₃GlcNAc₂ (M3), has been reported to enable cellular uptake of glycoproteins through the mannose receptor (MR) in humans, and such uptake has been exploited for the treatment of certain diseases. However, M3 is generally produced at a very low level in plants. In this study, a cell culture was established from an Arabidopsis alg3 mutant plant lacking asparagine-linked glycosylation 3 (ALG3) enzyme activity. Arabidopsis alg3 cell culture produced glycoproteins with predominantly M3 and GlcNAc-terminal structures, while the amount of plant-specific N-glycans was very low. Pharmaceutical glycoproteins with these characteristics would be valuable for cellular delivery through the MR, and safe for human therapy.

Biotechnology Applications of Cell-Free Expression Systems

Cell-free systems are a rapidly expanding platform technology with an important role in the engineering of biological systems. The key advantages that drive their broad adoption are increased efficiency, versatility, and low cost compared to in vivo systems. Traditionally, in vivo platforms have been used to synthesize novel and industrially relevant proteins and serve as a testbed for prototyping numerous biotechnologies such as genetic circuits and biosensors. Although in vivo platforms currently have many applications within biotechnology, they are hindered by time-constraining growth cycles, homeostatic considerations, and limited adaptability in production. Conversely, cell-free platforms are not hindered by constraints for supporting life and are therefore highly adaptable to a broad range of production and testing schemes. The advantages of cell-free platforms are being leveraged more commonly by the biotechnology community, and cell-free applications are expected to grow exponentially in the next decade. In this study, new and emerging applications of cell-free platforms, with a specific focus on cell-free protein synthesis (CFPS), will be examined. The current and near-future role of CFPS within metabolic engineering, prototyping, and biomanufacturing will be investigated as well as how the integration of machine learning is beneficial to these applications.

Glycoproteomic Characterization of FUT8 Knock-Out CHO Cells Reveals Roles of FUT8 in the Glycosylation

The α1,6-fucosyltransferase (encoded by FUT8 gene) is the key enzyme transferring fucose to the innermost GlcNAc residue on an N-glycan through an α-1,6 linkage in the mammalian cells. The presence of core fucose on antibody Fc region can inhibit antibody-dependent cellular cytotoxicity (ADCC) and reduce antibody therapeutic efficiency in vivo. Chinese hamster ovary (CHO) cells are the predominant production platform in biopharmaceutical manufacturing. Therefore, the generation of FUT8 knock-out (FUT8KO) CHO cell line is favorable and can be applied to produce completely non-fucosylated antibodies. The characterization of monoclonal antibodies as well as host cell glycoprotein impurities are required for quality control purposes under regulation rules. To understand the role of FUT8 in the glycosylation of CHO cells, we generated a FUT8 knock-out CHO cell line and performed a large-scale glycoproteomics to characterize the FUT8KO and wild-type (WT) CHO cells. The glycopeptides were enriched by hydrophilic chromatography and fractionated 25 fractions by bRPLC followed by analysis using high-resolution liquid chromatography mass spectrometry (LC-MS). A total of 7,127 unique N-linked glycosite-containing intact glycopeptides (IGPs), 928 glycosites, and 442 glycoproteins were identified from FUT8KO and WT CHO cells. Moreover, 28.62% in 442 identified glycoproteins and 26.69% in 928 identified glycosites were significantly changed in the FUT8KO CHO compared to wild-type CHO cells. The relative abundance of all the three N-glycan types (high-mannose, hybrid, and complex) was determined in FUT8KO comparing to wild-type CHO cells. Furthermore, a decrease in fucosylation content was observed in FUT8KO cells, in which core-fucosylated glycans almost disappeared as an effect of FUT8 gene knockout. Meantime, a total of 51 glycosylation-related enzymes were also quantified in these two cell types and 16 of them were significantly altered in the FUT8KO cells, in which sialyltransferases and glucosyltransferases were sharply decreased. These glycoproteomic results revealed that the knock-out of FUT8 not only influenced the core-fucosylation of proteins but also altered other glycosylation synthesis processes and changed the relative abundance of protein glycosylation.

Cross-identification of N-Glycans by CE-LIF using two capillary coatings and three labeling dyes

Recombinant protein biopharmaceuticals comprise a significant portion of the current drug development landscape. The glycosylation profile of these proteins is a key quality parameter as it can affect their safety, efficacy, and stability. However, glycan analysis is challenging because of the complexity of their structures. To overcome this challenge in achieving accurate glycan identification, cross-identification of N-Glycans by CE-LIF method using two capillary coatings and three labeling dyes was developed in this work. This work explored whether complementary separation capabilities can be achieved using homemade polyvinyl alcohol (PVA) coating and commercial Guarant™ (Guarant) coating in the analysis of N-glycans. Similar separation profiles were observed using the two capillary coatings, and hence the N-glycan GU databases generated by these coatings were comparable and complementary. The performance of cross-validation by labeling with three fluorescent dyes indicated that low covariance of APTS and Turquoise™ labeling can be obtained, and hence these two labeling mechanisms provided better accuracy for the identification of glycans. Superior reproducibility with RSDs less than 1% for all target glycan standards was achieved by the internal standards (IS) method using maltodextrin ladders as additives in the separation buffer. The developed CE-LIF analysis method was applied to the identification of N-glycans in IgG samples.

Genetic and process engineering strategies for enhanced recombinant N-glycoprotein production in bacteria

Background

The production of N-linked glycoproteins in genetically amenable bacterial hosts offers great potential for reduced cost, faster/simpler bioprocesses, greater customisation, and utility for distributed manufacturing of glycoconjugate vaccines and glycoprotein therapeutics. Efforts to optimize production hosts have included heterologous expression of glycosylation enzymes, metabolic engineering, use of alternative secretion pathways, and attenuation of gene expression. However, a major bottleneck to enhance glycosylation efficiency, which limits the utility of the other improvements, is the impact of target protein sequon accessibility during glycosylation.

Results

Here, we explore a series of genetic and process engineering strategies to increase recombinant N-linked glycosylation, mediated by the Campylobacter-derived PglB oligosaccharyltransferase in Escherichia coli. Strategies include increasing membrane residency time of the target protein by modifying the cleavage site of its secretion signal, and modulating protein folding in the periplasm by use of oxygen limitation or strains with compromised oxidoreductase or disulphide-bond isomerase activity. These approaches achieve up to twofold improvement in glycosylation efficiency. Furthermore, we also demonstrate that supplementation with the chemical oxidant cystine enhances the titre of glycoprotein in an oxidoreductase knockout strain by improving total protein production and cell fitness, while at the same time maintaining higher levels of glycosylation efficiency.

Conclusions

In this study, we demonstrate that improved protein glycosylation in the heterologous host could be achieved by mimicking the coordination between protein translocation, folding and glycosylation observed in native host such as Campylobacter jejuni and mammalian cells. Furthermore, it provides insight into strain engineering and bioprocess strategies, to improve glycoprotein yield and titre, and to avoid physiological burden of unfolded protein stress upon cell growth. The process and genetic strategies identified herein will inform further optimisation and scale-up of heterologous recombinant N-glycoprotein production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01689-x.

Studying the Expression Efficiencies of Human Clotting Factor IX Analogs, Rationally-designed for Hyper-glycosylation

Glyco-engineering has attracted lots of interest in studies dealing with the pharmacokinetics of therapeutic proteins. Based on our previous in-silico studies, two sites were selected in the N-terminal gamma-carboxy glutamic acid-rich (Gla) domain of the human clotting factor IX (hFIX) to add new N-glycosylation sites. Site-directed mutagenesis was employed to conduct K22N and R37N substitutions and introduce new N-glycosylation sites in the mature hFIX. The expression efficiencies of the mutants, in parallel with the wild-type hFIX (hFIX^wt), were assessed in suspension adapted Chinese hamster ovary (CHO-s) cells at transcriptional, translational, and post-translational levels. The transcription levels of both N-glycosylation mutants were significantly lower than that of the hFIX^wt. In contrast, at the protein level, the two hFIX mutants showed higher expression. The occurrence of hyper-glycosylation was only confirmed in the case of the hFIX^R37N mutant, which decreased the clotting activity. The higher expression of the hFIX mutants at protein level was evidenced, which could be attributed to higher protein stability, via omitting certain protease cleavage sites. The coagulation activity decline in the hyper-glycosylated hFIX^R37N mutant is probably due to the interference of the new N-glycan with protein-protein interactions in the coagulation cascade.

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.

Production of Human Acid-Alpha Glucosidase With a Paucimannose Structure by Glycoengineered Arabidopsis Cell Culture

Plant cell cultures have emerged as a promising platform for the production of biopharmaceutics due to their cost-effectiveness, safety, ability to control the cultivation, and secrete products into culture medium. However, the use of this platform is hindered by the generation of plant-specific N-glycans, the inability to produce essential N-glycans for cellular delivery of biopharmaceutics, and low productivity. In this study, an alternative acid-alpha glucosidase (GAA) for enzyme replacement therapy of Pompe disease was produced in a glycoengineered Arabidopsis alg3 cell culture. The N-glycan composition of the GAA consisted of a predominantly paucimannosidic structure, Man3GlcNAc2 (M3), without the plant-specific N-glycans. Supplementing the culture medium with NaCl to a final concentration of 50 mM successfully increased GAA production by 3.8-fold. GAA from an NaCl-supplemented culture showed a similar N-glycan profile, indicating that the NaCl supplementation did not affect N-glycosylation. The results of this study highlight the feasibility of using a glycoengineered plant cell culture to produce recombinant proteins for which M3 or mannose receptor-mediated delivery is desired.

Construction of a full-length antibody phage display vector

Antibody phage display technology plays an important role in the development of monoclonal antibodies, humanization, and affinity evolution of antibodies. Thus far, antibody phage display mainly focuses on the display of antibody variable region or antigen-binding fragments. In this study, we constructed a new phage display system that can display full-length IgG antibodies on M13 phage. The phage display vector contains open reading frames (ORFs) encoding full-length the heavy and light chains of the antibody. NcoI/XhoI restriction enzyme sites were used to clone the variable region of the heavy chain into the heavy chain ORF, and SalI/NotI sites were used to clone the light chain variable region. SnaBI and SbfI restriction enzyme sites were designed between the cloning sites of heavy and light chains, respectively, to increase the cloning efficiency. The full-length antibodies of nivolumab against programmed death factor 1, trastuzumab against human epidermal growth factor 2, diL2K against the cluster of differentiation 3 epsilon, and adalimumab against tumor necrosis factor- alpha were displayed on phage with the vector. Phage-displayed antibodies showed their original antigen-binding activity. An amber codon shifted the vector to express IgG in non-suppressed Escherichia coli. The heavy and light chains of the E. coli-expressed antibodies could be detected through western blotting, and the antigen-binding activity was confirmed using an enzyme-linked immunosorbent assay. Biopanning was carried out with a model phage display antibody library, and the results showed that the novel phage system could be used for antibody library construction and highly efficient antibody screening. The reported system is the first full-length antibody phage display system.

Galactosialidosis: preclinical enzyme replacement therapy in a mouse model of the disease, a proof of concept

Galactosialidosis is a rare lysosomal storage disease caused by a congenital defect of protective protein/cathepsin A (PPCA) and secondary deficiency of neuraminidase-1 and β-galactosidase. PPCA is a lysosomal serine carboxypeptidase that functions as a chaperone for neuraminidase-1 and β-galactosidase within a lysosomal multi-protein complex. Combined deficiency of the three enzymes leads to accumulation of sialylated glycoproteins and oligosaccharides in tissues and body fluids and manifests in a systemic disease pathology with severity mostly correlating with the type of mutation(s) and age of onset of the symptoms. Here, we describe a proof-of-concept, preclinical study toward the development of enzyme replacement therapy for galactosialidosis, using a recombinant human PPCA. We show that the recombinant enzyme, taken up by patient-derived fibroblasts, restored cathepsin A, neuraminidase-1, and β-galactosidase activities. Long-term, bi-weekly injection of the recombinant enzyme in a cohort of mice with null mutation at the PPCA (CTSA) locus (PPCA -/- ), a faithful model of the disease, demonstrated a dose-dependent, systemic internalization of the enzyme by cells of various organs, including the brain. This resulted in restoration/normalization of the three enzyme activities, resolution of histopathology, and reduction of sialyloligosacchariduria. These positive results underscore the benefits of a PPCA-mediated enzyme replacement therapy for the treatment of galactosialidosis.

Understanding the effect of increased cell specific productivity on galactosylation of monoclonal antibodies produced using Chinese hamster ovary cells

Achieving optimal productivity and desired product quality of the therapeutic monoclonal antibody (mAb) is one of the primary goals of process development. Across the various mAb programs at our company, we observed that increasing the specific productivity (q_p) results in a decrease in the % galactosylation (%Gal) level on the protein. In order to gain further insight into this correlation, cells were cultured under different process conditions such as pH or media osmolality or in the presence of supplements such as sodium butyrate. A range of q_p and N-glycan profiles were obtained with the greatest changes observed under high pH (lower q_p, higher %Gal), higher osmolality (higher q_p, lower %Gal) or sodium butyrate (moderately higher q_p, moderately lower %Gal) conditions. Abundance of individual glycan species highlighted different bottlenecks in the N-glycosylation pathway depending on the treatment condition. Transcriptomics analysis was performed to identify changes in gene expression profiles that correlate with the inverse relationship between q_p and %Gal. Results showed downregulation of Beta-1,4-galactosyltransferase 1 (B4GalT1), UDP-GlcNAc and Mn²⁺ transporter (slc35a3 and slc39a8 respectively) for the high osmolality conditions. Significant downregulation of slc39a8 (Mn²⁺ transporter) was observed for the sodium butyrate condition. No significant differences were observed for any of the genes in the N-glycosylation pathway under the high pH condition even though this condition showed highest %Gal. Together, data suggests that different treatments have distinct complex mechanisms by which the overall glycan levels of a mAb are influenced. Further studies based on these results will help build the knowledge necessary to design strategies to obtain the desired productivity and product quality of mAbs.

On-demand biomanufacturing of protective conjugate vaccines

Conjugate vaccines are among the most effective methods for preventing bacterial infections. However, existing manufacturing approaches limit access to conjugate vaccines due to centralized production and cold chain distribution requirements. To address these limitations, we developed a modular technology for in vitro conjugate vaccine expression (iVAX) in portable, freeze-dried lysates from detoxified, nonpathogenic Escherichia coli. Upon rehydration, iVAX reactions synthesize clinically relevant doses of conjugate vaccines against diverse bacterial pathogens in 1 hour. We show that iVAX-synthesized vaccines against Francisella tularensis subsp. tularensis (type A) strain Schu S4 protected mice from lethal intranasal F. tularensis challenge. The iVAX platform promises to accelerate development of new conjugate vaccines with increased access through refrigeration-independent distribution and portable production.

Recombinant H7 hemagglutinin expressed in glycoengineered Pichia pastoris forms nanoparticles that protect mice from challenge with H7N9 influenza virus

Cases of H7N9 human infection caused by an avian-origin H7N9 virus emerged in eastern China in 2013, leading to the urgent requirement of developing an effective vaccine to reduce its pandemic potential. In this report, the full-length recombinant H7 protein (rH7) of A/Hangzhou/1/2013 (H7N9) virus was expressed by a glycoengineered Pichia pastoris system. The rH7 protein underwent complex glycosylation modifications and polymerized to nanoparticles of 30-50 nm in diameter. Recombinant H7 (1.9 µg) elicited a > 1:40 hemagglutination inhibition titer, and 3.75 µg rH7 protected 100% of the mice in the mice challenge model with 10-fold 50% lethal dose of the A/Shanghai/2/2013 (H7N9) rat lung-adapted strain. In conclusion, rH7 produced by the glycoengineered P. pastoris can be used for vaccination against the H7N9 virus, and provides an effective platform for the rapid production of future influenza vaccines.

Cell-free systems for accelerating glycoprotein expression and biomanufacturing

Protein glycosylation, the enzymatic modification of amino acid sidechains with sugar moieties, plays critical roles in cellular function, human health, and biotechnology. However, studying and producing defined glycoproteins remains challenging. Cell-free glycoprotein synthesis systems, in which protein synthesis and glycosylation are performed in crude cell extracts, offer new approaches to address these challenges. Here, we review versatile, state-of-the-art systems for biomanufacturing glycoproteins in prokaryotic and eukaryotic cell-free systems with natural and synthetic N-linked glycosylation pathways. We discuss existing challenges and future opportunities in the use of cell-free systems for the design, manufacture, and study of glycoprotein biomedicines.

Modulation of Barley (Hordeum vulgare L.) Grain Protein Sink-Source Relations Towards Human Epidermal Growth Factor Instead of B-hordein Storage Protein

Seeds have evolutionarily developed to store protein without immediately degrading it and constitute ideal tissues for recombinant protein storage. Unfortunately, the production of recombinant protein in seeds is compromised by low yield as compared to other heterologous expression systems. In order to improve the yield of the human epidermal growth factor (EGF) in barley, protein sink-source relations in the developing grain were modulated towards EGF instead of the barley storage protein. The EGF gene, under the control of a B-hordein and a seed-specific oat globulin promoter, was introduced by crossing EGF lines into the Risø 56 mutant deficient in B-hordein storage protein synthesis. Offspring plants were analysed for EGF and Hordein expression and for expression of the unfolded protein response (UPR) genes PDI and CRT to monitor changes in ER stress levels. EGF content was increased significantly in the mature grain of homozygous offspring and PDI and CRT gene expressions were upregulated. We demonstrate, for the first time in barley, that replacement of an abundant seed storage protein with a specific heterologous protein driven by the promoter of the removed gene can accelerate the production of a specific heterologous protein in barley grains.

New advances and potentials of fungal immunomodulatory proteins for therapeutic purposes

Fungal immunomodulatory proteins (FIPs) are fascinating small and heat-stable bioactive proteins in a distinct protein family due to similarities in their structures and sequences. They are found in fungi, including the fruiting bodies producing fungi comprised of culinary and medicinal mushrooms. Structurally, most FIPs exist as homodimers; each subunit consisting of an N-terminal α-helix dimerization and a C-terminal fibronectin III domain. Increasing numbers of identified FIPs from either different or same fungal species clearly indicates the growing research interests into its medicinal properties which include immunomodulatory, anti-inflammation, anti-allergy, and anticancer. Most FIPs increased IFN-γ production in peripheral blood mononuclear cells, potentially exerting immunomodulatory and anti-inflammatory effects by inhibiting overproduction of T helper-2 (Th2) cytokines common in an allergy reaction. Recently, FIP from Ganoderma microsporum (FIP-gmi) was shown to promote neurite outgrowth for potential therapeutic applications in neuro-disorders. This review discussed FIPs' structural and protein characteristics, their recombinant protein production for functional studies, and the recent advances in their development and applications as pharmaceutics and functional foods.

Glycoprotein- and Lectin-Based Approaches for Detection of Pathogens

Infectious diseases alone are estimated to result in approximately 40% of the 50 million total annual deaths globally. The importance of basic research in the control of emerging and re-emerging diseases cannot be overemphasized. However, new nanotechnology-based methodologies exploiting unique surface-located glycoproteins or their patterns can be exploited to detect pathogens at the point of use or on-site with high specificity and sensitivity. These technologies will, therefore, affect our ability in the future to more accurately assess risk. The critical challenge is making these new methodologies cost-effective, as well as simple to use, for the diagnostics industry and public healthcare providers. Miniaturization of biochemical assays in lab-on-a-chip devices has emerged as a promising tool. Miniaturization has the potential to shape modern biotechnology and how point-of-care testing of infectious diseases will be performed by developing smart microdevices that require minute amounts of sample and reagents and are cost-effective, robust, and sensitive and specific. The current review provides a short overview of some of the futuristic approaches using simple molecular interactions between glycoproteins and glycoprotein-binding molecules for the efficient and rapid detection of various pathogens at the point of use, advancing the emerging field of glyconanodiagnostics.

Engineering orthogonal human O-linked glycoprotein biosynthesis in bacteria

A major objective of synthetic glycobiology is to re-engineer existing cellular glycosylation pathways from the top down or construct non-natural ones from the bottom up for new and useful purposes. Here, we have developed a set of orthogonal pathways for eukaryotic O-linked protein glycosylation in Escherichia coli that installed the cancer-associated mucin-type glycans Tn, T, sialyl-Tn and sialyl-T onto serine residues in acceptor motifs derived from different human O-glycoproteins. These same glycoengineered bacteria were used to supply crude cell extracts enriched with glycosylation machinery that permitted cell-free construction of O-glycoproteins in a one-pot reaction. In addition, O-glycosylation-competent bacteria were able to generate an antigenically authentic Tn-MUC1 glycoform that exhibited reactivity with antibody 5E5, which specifically recognizes cancer-associated glycoforms of MUC1. We anticipate that the orthogonal glycoprotein biosynthesis pathways developed here will provide facile access to structurally diverse O-glycoforms for a range of important scientific and therapeutic applications.

Synthetic Glycobiology: Parts, Systems, and Applications

Protein glycosylation, the attachment of sugars to amino acid side chains, can endow proteins with a wide variety of properties of great interest to the engineering biology community. However, natural glycosylation systems are limited in the diversity of glycoproteins they can synthesize, the scale at which they can be harnessed for biotechnology, and the homogeneity of glycoprotein structures they can produce. Here we provide an overview of the emerging field of synthetic glycobiology, the application of synthetic biology tools and design principles to better understand and engineer glycosylation. Specifically, we focus on how the biosynthetic and analytical tools of synthetic biology have been used to redesign glycosylation systems to obtain defined glycosylation structures on proteins for diverse applications in medicine, materials, and diagnostics. We review the key biological parts available to synthetic biologists interested in engineering glycoproteins to solve compelling problems in glycoscience, describe recent efforts to construct synthetic glycoprotein synthesis systems, and outline exemplary applications as well as new opportunities in this emerging space.

Sequential Glycosylation of Proteins with Substrate-Specific N-Glycosyltransferases

Protein glycosylation is a common post-translational modification that influences the functions and properties of proteins. Despite advances in methods to produce defined glycoproteins by chemoenzymatic elaboration of monosaccharides, the understanding and engineering of glycoproteins remain challenging, in part, due to the difficulty of site-specifically controlling glycosylation at each of several positions within a protein. Here, we address this limitation by discovering and exploiting the unique, conditionally orthogonal peptide acceptor specificities of N-glycosyltransferases (NGTs). We used cell-free protein synthesis and mass spectrometry of self-assembled monolayers to rapidly screen 41 putative NGTs and rigorously characterize the unique acceptor sequence preferences of four NGT variants using 1254 acceptor peptides and 8306 reaction conditions. We then used the optimized NGT-acceptor sequence pairs to sequentially install monosaccharides at four sites within one target protein. This strategy to site-specifically control the installation of N-linked monosaccharides for elaboration to a variety of functional N-glycans overcomes a major limitation in synthesizing defined glycoproteins for research and therapeutic applications.

Glycoengineering bioconjugate vaccines, therapeutics, and diagnostics in E. coli

The first, general glycosylation pathway in bacteria, the N-linked glycosylation system of Campylobacter jejuni, was discovered two decades ago. Since then, many diverse prokaryotic glycosylation systems have been characterized, including O-linked glycosylation systems that have no homologous counterparts in eukaryotic organisms. Shortly after these discoveries, glycosylation pathways were recombinantly introduced into E. coli creating the field of bacterial glycoengineering. Bacterial glycoengineering is an emerging biotechnological tool that harnesses prokaryotic glycosylation systems for the generation of recombinantly glycosylated proteins using E. coli as a host. Over the last decade, as our understanding of prokaryotic glycosylation systems has advanced, so too has the glycoengineering toolbox. Currently, glycoengineering utilizes two broad approaches to recombinantly glycosylate proteins, both of which can generate N- or O-linkages: oligosaccharyltransferase (OTase)-dependent and OTase-independent. This review discusses the applications of these bacterial glycoengineering techniques as they relate to the development of glycoconjugate vaccines, therapeutic proteins, and diagnostics.

ProGlycProt V2.0, a repository of experimentally validated glycoproteins and protein glycosyltransferases of prokaryotes

Knowledge of glycosylation status and glycan-pattern of proteins are of considerable medical, academic and application interest. ProGlycProt V2.0 (www.proglycprot.org) therefore, is conceived and maintained as an exclusive web-resource providing comprehensive information on experimentally validated glycoproteins and protein glycosyltransferases (GTs) of prokaryotic origin. The second release of ProGlycProt features a major update with a 191% increase in the total number of entries, manually collected and curated from 607 peer-reviewed publications, on the subject. Protein GTs from prokaryotes that catalyze a varied range of glycan linkages are amenable glycoengineering tools. Therefore, the second release presents content that is greatly expanded and reorganized in two sub-databases: ProGPdb and ProGTdb. While ProGPdb provides information about validated glycoproteins (222 entries), ProGTdb catalogs enzymes/proteins that are instrumental in protein glycosylation, directly (122) or as accessory proteins (182). ProGlycProt V2.0 remains highly cross-referenced yet exclusive and complementary in content to other related databases. The second release further features enhanced search capability, a "compare" entries option and an innovative geoanalytical tool (MapView) facilitating location-assisted search-cum filtering of the entries using geo-positioning information of researchers/groups cited in the ProGlycProt V2.0 databases. Thus, ProGlycProt V2.0 continues to serve as a useful one-point web-resource on various evidence-based information on protein glycosylation in prokaryotes.

A cell-free biosynthesis platform for modular construction of protein glycosylation pathways

Glycosylation plays important roles in cellular function and endows protein therapeutics with beneficial properties. However, constructing biosynthetic pathways to study and engineer precise glycan structures on proteins remains a bottleneck. Here, we report a modular, versatile cell-free platform for glycosylation pathway assembly by rapid in vitro mixing and expression (GlycoPRIME). In GlycoPRIME, glycosylation pathways are assembled by mixing-and-matching cell-free synthesized glycosyltransferases that can elaborate a glucose primer installed onto protein targets by an N-glycosyltransferase. We demonstrate GlycoPRIME by constructing 37 putative protein glycosylation pathways, creating 23 unique glycan motifs, 18 of which have not yet been synthesized on proteins. We use selected pathways to synthesize a protein vaccine candidate with an α-galactose adjuvant motif in a one-pot cell-free system and human antibody constant regions with minimal sialic acid motifs in glycoengineered Escherichia coli. We anticipate that these methods and pathways will facilitate glycoscience and make possible new glycoengineering applications.

Constructing biosynthetic pathways to study and engineer glycoprotein structures is difficult. Here, the authors use GlycoPRIME, a cell-free workflow for mixing-and-matching glycosylation enzymes, to evaluate 37 putative glycosylation pathways and discover routes to 18 new glycoprotein structures

Coexpression of CMP-sialic acid transporter reduces N-glycolylneuraminic acid levels of recombinant glycoproteins in Chinese hamster ovary cells

Recombinant glycoproteins expressed in Chinese hamster ovary (CHO) cells contain two forms of sialic acids; N-acetylneuraminic acid (Neu5Ac) as a major type and N-glycolylneuraminic acid (Neu5Gc) as a minor type. The Neu5Gc glycan moieties in therapeutic glycoproteins can elicit immune responses because they do not exist in human. In the present work, to reduce Neu5Gc levels of recombinant glycoproteins from CHO cell cultures, we coexpressed cytidine-5'-monophosphate-sialic acid transporter (CMP-SAT) that is an antiporter and transports cytosolic CMP-sialic acids (both forms) into Golgi lumen. When human erythropoietin was used as a target human glycoprotein, coexpression of CMP-SAT resulted in a significant decrease of Neu5Gc level by 41.4% and a notable increase of Neu5Ac level by 21.2%. This result could be reasonably explained by our hypothesis that the turnover rate of Neu5Ac to Neu5Gc catalyzed by CMP-Neu5Ac hydroxylase would be reduced through facilitated transportation of Neu5Ac into Golgi apparatus by coexpression of CMP-SAT. We confirmed the effects of CMP-SAT coexpression on the decrease of Neu5Gc level and the increase of Neu5Ac level using another glycoprotein human DNase I. Therefore, CMP-SAT coexpression might be an effective strategy to reduce the levels of undesired Neu5Gc in recombinant therapeutic glycoproteins from CHO cell cultures.

An Introduction to "Recent Trends in the Biotechnology Industry: Development and Manufacturing of Recombinant Antibodies and Proteins"

The production of the first therapeutic proteins in the early 1980s heralded the launch of the biopharmaceuticals industry. The number of approved products has grown year on year over the past three decades to now represent a significant share of the entire pharmaceuticals market. More than 200 therapeutic proteins have been approved, approximately a quarter of which are represented by monoclonal antibodies and their derivatives. In 2016, the list of the top 15 best-selling drugs included more than eight biologics and in 2020 the trend will continue, with more than 50% of the top 20 best-selling drugs predicted to be biologics. From 1986 to 2014 several first-in-class, advance-in-class, and breakthrough designated therapeutic options were approved, with advanced therapies such as immuno-oncology and cell-based therapies being approved for several indications.

The glycosylation design space for recombinant lysosomal replacement enzymes produced in CHO cells

Lysosomal replacement enzymes are essential therapeutic options for rare congenital lysosomal enzyme deficiencies, but enzymes in clinical use are only partially effective due to short circulatory half-life and inefficient biodistribution. Replacement enzymes are primarily taken up by cell surface glycan receptors, and glycan structures influence uptake, biodistribution, and circulation time. It has not been possible to design and systematically study effects of different glycan features. Here we present a comprehensive gene engineering screen in Chinese hamster ovary cells that enables production of lysosomal enzymes with N-glycans custom designed to affect key glycan features guiding cellular uptake and circulation. We demonstrate distinct circulation time and organ distribution of selected glycoforms of α-galactosidase A in a Fabry disease mouse model, and find that an α2-3 sialylated glycoform designed to eliminate uptake by the mannose 6-phosphate and mannose receptors exhibits improved circulation time and targeting to hard-to-reach organs such as heart. The developed design matrix and engineered CHO cell lines enables systematic studies towards improving enzyme replacement therapeutics.

Lysosomal replacement enzymes are taken up by cell surface receptors that recognize glycans, the effects of different glycan features are unknown. Here the authors present a gene engineering screen in CHO cells that allows custom N-glycan-decorated enzymes with improved circulation time and organ distribution.

Increased branching and sialylation of N-linked glycans correlate with an improved pharmacokinetic profile for BAY 81-8973 compared with other full-length rFVIII products

Background

BAY 81-8973 (Kovaltry) is an unmodified full-length recombinant factor VIII (rFVIII) for treatment of hemophilia A. The BAY 81-8973 manufacturing process results in a product of enhanced purity with a consistently high degree of branching and sialylation of N-linked glycans. This study evaluated whether a relationship exists between N-linked glycosylation patterns of BAY 81-8973 and two other rFVIII (sucrose-formulated rFVIII [rFVIII-FS; Kogenate FS]) and antihemophilic factor (recombinant) plasma/albumin-free method (rAHF-PFM; Advate) and their pharmacokinetic (PK) characteristics.

Materials and methods

N-linked glycans or terminal carbohydrates were enzymatically removed from immobilized BAY 81-8973, rFVIII-FS, and rAHF-PFM proteins and analyzed using high-performance liquid chromatography to determine the percentage of individual N-linked glycan structures and degree of sialylation of each structure. PK data were available from two separate phase 1 crossover studies in which the PK profile of BAY 81-8973 was compared with that of rFVIII-FS (n=26) and rAHF-PFM (n=18) in patients with severe hemophilia A who received a single 50 IU/kg dose of each product.

Results

BAY 81-8973 and rFVIII-FS had increased N-linked glycan branching with higher levels of sialylation compared with rAHF-PFM. Levels of trisialylated glycans were 29.0% for BAY 81-8973 vs 11.5% for rFVIII-FS and 4.8%-5.5% for rAHF-PFM; tetrasialylated glycans were 12.0% vs 2.8% and 0.6%, respectively. Degree of sialylation was 96% for BAY 81-8973, 94% for rFVIII-FS, and 78%-81% for rAHF-PFM. Based on chromogenic assay results from the single-dose phase 1 PK studies, BAY 81-8973 half-life was 15% longer than that for rFVIII-FS and 16% longer than rAHF-PFM.

Conclusion

Increased N-glycan branching and sialylation were seen for BAY 81-8973 vs rFVIII-FS and rAHF-PFM. Improved PK for BAY 81-8973 relative to rFVIII-FS and rAHF-PFM as seen in single-dose crossover PK studies might be related to this greater level of branching and sialylation, which can prolong the time BAY 81-8973 remains in the circulation.

Medaka follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh): Developmental profiles of pituitary protein and gene expression levels

The two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) are of particular importance within the hypothalamic-pituitary-gonadal (HPG) axis of vertebrates. In the current study, we demonstrate the production and validation of Japanese medaka (Oryzias latipes) recombinant (md) gonadotropins Fshβ (mdFshβ), Lhβ (mdLhβ), Fshβα (mdFshβα), and Lhβα (mdLhβα) by Pichia pastoris, the generation of specific rabbit antibodies against their respective β subunits, and their use within the development and validation of competitive enzyme-linked immunosorbent assays (ELISAs) for quantification of medaka Fsh and Lh. mdFsh and mdLh were produced as single-chain polypeptides by linking the α subunit with mdFshβ or mdLhβ mature protein coding sequences to produce a "tethered" polypeptide with the β-chain at the N-terminal and the α-chain at the C-terminal. The specificity of the antibodies raised against mdFshβ and mdLhβ was determined by immunofluorescence (IF) for Fshβ and Lhβ on medaka pituitary tissue, while comparison with fluorescence in situ hybridization (FISH) for fshb and lhb mRNA was used for validation. Competitive ELISAs were developed using antibodies against mdFshβ or mdLhβ, and the tethered proteins mdFshβα or mdLhβα for standard curves. The standard curve for the Fsh ELISA ranged from 97.6 pg/ml to 50 ng/ml, and for the Lh ELISA from 12.21 pg/ml to 6.25 ng/ml. The sensitivity of the assays for Fsh and Lh was 44.7 and 70.8 pg/ml, respectively. A profile of pituitary protein levels of medaka Fsh and Lh comparing juveniles with adults showed significant increase of protein amount from juvenile group (body length from 12 mm to 16.5 mm) to adult group (body length from 21 mm to 26.5 mm) for both hormones in male medaka. Comparing these data to a developmental profile of pituitary mRNA expression of medaka fshb and lhb, the mRNA expression of lhb also increased during male maturation and a linear regression analysis revealed a significant increase of lhb expression with increased body length that proposes a linear model. However, fshb mRNA expression did not change significantly during male development and therefore was not correlated with body length. In summary, we have developed and validated homologous ELISA assays for medaka Fsh and Lh based on proteins produced in P. pastoris, assays that will be used to study the functions and regulations of Fsh and Lh in more detail.

Protein Glycosylation through Sulfur Fluoride Exchange (SuFEx) Chemistry: The Key Role of a Fluorosulfate Thiolactoside

Protein glycosylation is the most complex post-translational modification process. More than 50 % of human cells proteins are glycosylated, whereas bacteria such as E. coli do not have this modification machinery. Indeed, the carbohydrate residues in natural proteins affect their folding, immunogenicity, and stability toward proteases, besides controlling biological properties and activities. It is therefore important to introduce such structural modification in bioengineered proteins lacking the presence of carbohydrate residues. This is not trivial as it requires reagents and conditions compatible with the protein's stability and reactivity. This work reports on the introduction of lactose moieties in two natural proteins, namely ubiquitin (Ub) and l-asparaginase II (ANSII). The synthetic route employed is based on the sulfur(VI) fluoride exchange (SuFEx) coupling of a lactose tethered arylfluorosulfate (Lact-Ar-OSO₂ F) with the ϵ-NH₂ group of lysine residues of the proteins. This metal-free click SuFEx reaction relies on the properties of the fluorosulfate employed, which is easily prepared in multigram scale from available precursors and reacts chemoselectively with the ϵ-NH₂ group of lysine residues under mild conditions. Thus, iterative couplings of Lact-Ar-OSO₂ F to Ub and ANSII, afforded multiple glycosylations of these proteins so that up to three and four Lact-Ar-OSO₂ groups were introduced in Ub and ANSII, respectively, via the formation of a sulfamoyl (OSO₂ -NH) linkage.

PiggyBac-based screening identified BEM4 as a suppressor to rescue growth defects in och1-disrupted yeast cells

Glycoengineered yeast cells, which express human-compatible glycan structures, are particularly attractive host cells to produce therapeutic glycoproteins. Disruption of OCH1 gene, which encodes an α-1,6-mannosyltransferase required for mannan-type N-glycan formation, is essential for the elimination of yeast-specific N-glycan structures. However, the gene disruption causes cell wall defects leading to growth defects. Here, we tried to identify factors to rescue the growth defects of och1Δ cells by in vivo mutagenesis using piggyBac (PB)-based transposon. We isolated a mutant strain, named 121, which could grow faster than parental och1Δ cells. The PB element was introduced into the promoter region of BEM4 gene and upregulated the BEM4 expression. Overexpression of BEM4 suppressed growth defects in och1Δ cells. The slow grow phenotypes were partially rescued by expression of Rho1p, whose function is regulated by Bem4p. Our results indicate that BEM4 would be useful to produce therapeutic proteins in glycoengineered yeast without the growth defects.

Design of glycosylation sites by rapid synthesis and analysis of glycosyltransferases

Glycosylation is an abundant post-translational modification that is important in disease and biotechnology. Current methods to understand and engineer glycosylation cannot sufficiently explore the vast experimental landscapes required to accurately predict and design glycosylation sites modified by glycosyltransferases. Here we describe a systematic platform for glycosylation sequence characterization and optimization by rapid expression and screening (GlycoSCORES), which combines cell-free protein synthesis and mass spectrometry of self-assembled monolayers. We produced six N- and O-linked polypeptide-modifying glycosyltransferases from bacteria and humans in vitro and rigorously determined their substrate specificities using 3,480 unique peptides and 13,903 unique reaction conditions. We then used GlycoSCORES to optimize and design small glycosylation sequence motifs that directed efficient N-linked glycosylation in vitro and in the Escherichia coli cytoplasm for three heterologous proteins, including the human immunoglobulin Fc domain. We find that GlycoSCORES is a broadly applicable method to facilitate fundamental understanding of glycosyltransferases and engineer synthetic glycoproteins.

Hollow microcarriers for large-scale expansion of anchorage-dependent cells in a stirred bioreactor

With recent advances in biotechnology, mammalian cells are used in biopharmaceutical industries to produce valuable protein therapeutics and investigated as effective therapeutic agents to permanently degenerative diseases in cell based therapy. In these exciting and actively expanding fields, a reliable, efficient, and affordable platform to culture mammalian cells on a large scale is one of the most vital necessities. To produce and maintain a very large population of anchorage-dependent cells, a microcarrier-based stirred tank bioreactor is commonly used. In this approach, the cells are exposed to harmful hydrodynamic shear stress in the bioreactor and the mass transfer rates of nutrients and gases in the bioreactor are often kept below an optimal level to prevent cellular damages from the shear stress. In this paper, a hollow microcarrier (HMC) is presented as a novel solution to protect cells from shear stress in stirred bioreactors, while ensuring sufficient and uniform mass transfer rate of gases and nutrients. HMC is a hollow microsphere and cells are cultured on its inner surface to be protected, while openings on the HMC provide sufficient exchange of media inside the HMC. As a proof of concept, we demonstrated the expansion of fibroblasts, NIH/3T3 and the expansion and cardiac differentiation of human induced pluripotent stem cells, along with detailed numerical analysis. We believe that the developed HMC can be a practical solution to enable large-scale expansion of shear-sensitive anchorage-dependent cells in an industrial scale with stirred bioreactors.

The ENGases: versatile biocatalysts for the production of homogeneous N-linked glycopeptides and glycoproteins

The endo-β-N-acetylglucosaminidases (ENGases) are an enzyme class (EC 3.2.1.96) produced by a range of organisms, ranging from bacteria, through fungi, to higher order species, including humans, comprising two-sub families of glycosidases which all cleave the chitobiose core of N-linked glycans. Synthetic applications of these enzymes, i.e. to catalyse the reverse of their natural hydrolytic mode of action, allow the attachment of N-glycans to a wide variety of substrates which contain an N-acetylglucosamine (GlcNAc) residue to act as an 'acceptor' handle. The use of N-glycan oxazolines, high energy intermediates on the hydrolytic pathway, as activated donors allows their high yielding attachment to almost any amino acid, peptide or protein that contains a GlcNAc residue as an acceptor. The synthetic effectiveness of these biocatalysts has been significantly increased by the production of mutant glycosynthases; enzymes which can still catalyse synthetic processes using oxazolines as donors, but which do not hydrolyse the reaction products. ENGase biocatalysts are now finding burgeoning application for the production of biologically active glycopeptides and glycoproteins, including therapeutic monoclonal antibodies (mAbs) for which the oligosaccharides have been remodelled to optimise effector functions.

Platforms for Recombinant Therapeutic Glycoprotein Production

The majority of FDA-approved biology-derived products are recombinant glycoproteins. These proteins have been used for the treatment of several diseases, with numerous products currently approved for clinical use. The choice of the expression system is a key step toward a successful functional protein production, since glycosylation influences yield, pharmacokinetics, biological activity, and immunogenicity. This chapter covers the general aspects of therapeutic recombinant glycoproteins and the platforms that are being employed for their production.

Bacterial Glycoengineering as a Biosynthetic Route to Customized Glycomolecules

Bacteria have garnered increased interest in recent years as a platform for the biosynthesis of a variety of glycomolecules such as soluble oligosaccharides, surface-exposed carbohydrates, and glycoproteins. The ability to engineer commonly used laboratory species such as Escherichia coli to efficiently synthesize non-native sugar structures by recombinant expression of enzymes from various carbohydrate biosynthesis pathways has allowed for the facile generation of important products such as conjugate vaccines, glycosylated outer membrane vesicles, and a variety of other research reagents for studying and understanding the role of glycans in living systems. This chapter highlights some of the key discoveries and technologies for equipping bacteria with the requisite biosynthetic machinery to generate such products. As the bacterial glyco-toolbox continues to grow, these technologies are expected to expand the range of glycomolecules produced recombinantly in bacterial systems, thereby opening up this platform to an even larger number of applications.