N- and O-linked carbohydrates and glycosylation site occupancy in recombinant human granulocyte-macrophage colony-stimulating factor secreted by a Chinese hamster ovary cell line

A comprehensive study of glucose and oxygen gradients in a scaled-down model of recombinant HuGM-CSF production in thermoinduced Escherichia coli fed-batch cultures

The effect of gradients of elevated glucose and low dissolved oxygen in the addition zone of fed-batch E. coli thermoinduced recombinant high cell density cultures can be evaluated through two-compartment scale-down models. Here, glucose was fed in the inlet of a plug flow bioreactor (PFB) connected to a stirred tank bioreactor (STB). E. coli cells diminished growth from 48.2 ± 2.2 g/L in the stage of RP production if compared to control (STB) with STB-PFB experiments, when residence time inside the PFB was 25 s (34.1 ± 3.5 g/L) and 40 s (25.6 ± 5.1 g/L), respectively. The recombinant granulocyte-macrophage colony-stimulating factor (rHuGM-CSF) production decreased from 34 ± 7% of RP in inclusion bodies (IB) in control cultures to 21 ± 8%, and 7 ± 4% during the thermoinduction production phase when increasing residence time inside the PFB to 25 s and 40 s, respectively. This, along with the accumulation of acetic and formic acid (up to 4 g/L), indicates metabolic redirection of central carbon routes through metabolic flow and mixed acid fermentation. Special care must be taken when producing a recombinant protein in heat-induced E. coli, because the yield and productivity of the protein decreases as the size of the bioreactors increases, especially if they are carried at high cell density.

Generation and Characterization of Stable Redox-Reporter Mammalian Cell Lines of Biotechnological Relevance

Cellular functions such as DNA replication and protein translation are influenced by changes in the intracellular redox milieu. Exogenous (i.e., nutrients, deterioration of media components, xenobiotics) and endogenous factors (i.e., metabolism, growth) may alter the redox homeostasis of cells. Thus, monitoring redox changes in real time and in situ is deemed essential for optimizing the production of recombinant proteins. Recently, different redox-sensitive variants of green fluorescent proteins (e.g., rxYFP, roGFP2, and rxmRuby2) have been engineered and proved suitable to detect, in a non-invasive manner, perturbations in the pool of reduced and oxidized glutathione, the major low molecular mass thiol in mammals. In this study, we validate the use of cytosolic rxYFP on two cell lines widely used in biomanufacturing processes, namely, CHO-K1 cells expressing the human granulocyte macrophage colony-stimulating factor (hGM-CSF) and HEK-293. Flow cytometry was selected as the read-out technique for rxYFP signal given its high-throughput and statistical robustness. Growth kinetics and cellular metabolism (glucose consumption, lactate and ammonia production) of the redox reporter cells were comparable to those of the parental cell lines. The hGM-CSF production was not affected by the expression of the biosensor. The redox reporter cell lines showed a sensitive and reversible response to different redox stimuli (reducing and oxidant reagents). Under batch culture conditions, a significant and progressive oxidation of the biosensor occurred when CHO-K1-hGM-CSF cells entered the late-log phase. Medium replenishment restored, albeit partially, the intracellular redox homeostasis. Our study highlights the utility of genetically encoded redox biosensors to guide metabolic engineering or intervention strategies aimed at optimizing cell viability, growth, and productivity.

Plant-Expressed Receptor Binding Domain of the SARS-CoV-2 Spike Protein Elicits Humoral Immunity in Mice

The current 15-month coronavirus disease-19 (COVID-19) pandemic caused by SARS-CoV-2 has accounted for 3.77 million deaths and enormous worldwide social and economic losses. A high volume of vaccine production is urgently required to eliminate COVID-19. Inexpensive and robust production platforms will improve the distribution of vaccines to resource-limited countries. Plant species offer such platforms, particularly through the production of recombinant proteins to serve as immunogens. To achieve this goal, here we expressed the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein in the glycoengineered-tobacco plant Nicotiana benthamiana to provide a candidate subunit vaccine. This recombinant RBD elicited humoral immunity in mice via induction of highly neutralizing antibodies. These findings provide a strong foundation to further advance the development of plant-expressed RBD antigens for use as an effective, safe, and inexpensive SARS-CoV-2 vaccine. Moreover, our study further highlights the utility of plant species for vaccine development.

Characterization of a novel + 70 Da modification in rhGM-CSF expressed in E. coli using chemical assays in combination with mass spectrometry

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine and a white blood cell growth factor that has found usage as a therapeutic protein. During analysis of different fermentation batches of GM-CSF recombinantly expressed in E. coli, a covalent modification was identified on the protein by intact mass spectrometry. The modification gave a mass shift of + 70 Da and peptide mapping analysis demonstrated that it located to the protein N-terminus and lysine side chains. The chemical composition of C₄H₆O was found to be the best candidate by peptide fragmentation using tandem mass spectrometry. The modification likely contains a carbonyl group, since the mass of the modification increased by 2 Da by reduction with borane pyridine complex and it reacted with 2,4-dinitrophenylhydrazine. On the basis of chemical and tandem mass spectrometry fragmentation behavior, the modification could be attributed to crotonaldehyde, a reactive compound formed during lipid peroxidation. A low recorded oxygen pressure in the reactor during protein expression could be linked to the formation of this compound. This study shows the importance of maintaining full control over all reaction parameters during recombinant protein production.

Granulocyte-macrophage colony stimulating factor (GM-CSF) is fully expressed in the genital tract, seminal plasma and spermatozoa of male pigs

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a pro-inflammatory cytokine identified in boar seminal plasma (SP) but until now unexplored in terms of place of production and its association to spermatozoa. This study aimed to explore these aspects by evaluating the presence of GM-CSF in porcine reproductive organs (testes, epididymis and accessory sex glands), SP and mature spermatozoa (from cauda epididymis and ejaculated) using Western blot (WB), immunohistochemistry and immunocytochemistry. Positive labelling was obtained in tissues, SP and spermatozoa. In reproductive organs, WB revealed three forms of GM-CSF with different glycosylation degrees (15, 31 and 40 kDa). In SP and epididymal fluid, the GM-CSF appeared only in its active form while in spermatozoa the GM-CSF form present varied among sperm sources. Non-viable spermatozoa showed more GM-CSF than viable spermatozoa (14.87 ± 1.98 RU vs. 7.25 ± 0.52 RU) of fluorescence intensity. In conclusion, GM-CSF is widely present in the reproductive tract of male pigs, attached to the spermatozoa already in the epididymis as well as verted to SP. Consequently, the GM-CSF ought to regulate male genital tract and sperm function as well as mediating initial inflammatory responses and further mediating later immune actions by the female to semen deposition.

A Novel Methanol-Free Platform for Extracellular Expression of rhGM-CSF in Pichia pastoris

The production of the recombinant proteins under the control of AOX1 promoter is a one of the most common expression systems in the methylotrophic yeast Pichia pastoris which is induced by methanol. The application of this expression platform is restricted by the toxicity and inflammatory nature of methanol, especially in food and pharmaceutical products. Human granulocyte macrophage-colony stimulating factor (hGM-CSF) is an important pharmaceutical protein, playing a crucial role in the proliferation and differentiation of innate immune cells. In this study, a methanol-free expression platform for extracellular expression of hGM-CSF was developed. To attain this goal, a novel constructed expression vector pEP(α)101, carrying the FMD promoter regulating recombinant expression by glycerol derepression was designed. The optimized hGM-CSF gene was subcloned into pEP(α)101 and transformed into P. pastoris. The expression of rhGM-CSF in three different culture media were investigated. Based on the observed heterogeneous glycosylation pattern on SDS-PAGE and western blot, the glycoproteins were deglycosylated to remove carbohydrate units. According to the results, the novel methanol independent P_FMD expression platform would be a suitable candidate for driving heterologous gene expression especially for the production of food-grade and therapeutically important recombinant proteins.

Assay system development to measure the concentration of sargramostim with high specificity in patients with autoimmune pulmonary alveolar proteinosis after single-dose inhalation

During a clinical trial of a Saccharomyces cerviciae-derived recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF), sargramostim, in patients with autoimmune pulmonary alveolar proteinosis (aPAP), we conducted a pharmacokinetic study of single-dose sargramostim inhalation. Several problems were encountered whereby sargramostim formed an immune-complex with GM-CSF autoantibodies (GMAbs) immediately after entering the body; thus, we could not measure the concentration of sargramostim using a commercial high sensitivity enzyme-linked immunosorbent assay (ELISA). Moreover, the ELISA could not discriminate inhaled sargramostim from intrinsic GM-CSF. To solve these problems, we developed a novel ELISA system with a capture antibody that is specific for sargramostim and a detection antibody capable of binding with GM-CSF. This system quantified the serum sargramostim concentration, but not E. coli-, CHO-, or HEK293T-derived human recombinant GM-CSF. Using this system, serum pharmacokinetics were estimated in five patients after inhalation of 250 μg sargramostim, with a mean Cmax of 9.7 ± 2.85 pg/ml at a Tmax of 2 ± 1.22 h.

Quantification of N-glycosylation site occupancy status based on labeling/label-free strategies with LC-MS/MS

Protein N-glycosylation plays important roles in physiological and pathological processes. Characterizing the site-specific N-glycosylation including N-glycan macroheterogeneity (glycosylation site occupancy) and microheterogeneity (site-specific glycan structure) is important for understanding of glycoprotein biosynthesis and function. N-Glycan macroheterogeneity is a physiological property of glycoprotein and the technical obstacles have restricted research into the regulation and functions of this heterogeneity. Quantification of N-glycosylation site occupancy would uncover the critical role of macroheterogeneity in a variety of biological properties. Liquid chromatography (LC)- mass spectrometry (MS)-based quantification is emerging as a powerful tool for glycosylation characterization. This review summarizes the labeling and label-free quantitative MS approaches for quantifying N-glycosylation site occupancy, including its quantification for target glycoproteins in recent years.

Biological roles of glycans

Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

DNA-protein immunization using Leishmania peroxidoxin-1 induces a strong CD4+ T cell response and partially protects mice from cutaneous leishmaniasis: role of fusion murine granulocyte-macrophage colony-stimulating factor DNA adjuvant

BACKGROUND

To date, no universally effective and safe vaccine has been developed for general human use. Leishmania donovani Peroxidoxin-1 (LdPxn-1) is a member of the antioxidant family of proteins and is predominantly expressed in the amastigote stage of the parasite. The aim of this study was to evaluate the immunogenicity and protective efficacy of LdPxn-1 in BALB/c mice in heterologous DNA-Protein immunization regimen in the presence of fusion murine granulocyte-macrophage colony-stimulating factor (mGMCSF) DNA adjuvant.

METHODOLOGY AND PRINCIPAL FINDINGS

A fusion DNA of LdPxn1 and mGMCSF was cloned into a modified pcDNA vector. To confirm the expression in mammalian system, Chinese hamster ovary cells were transfected with the plasmid vector containing LdPxn1 gene. BALB/c mice were immunized twice with pcDNA-mGMCSF-LdPxn-1 or pcDNA-LdPxn1 DNA and boosted once with recombinant LdPxn-1 protein. Three weeks after the last immunization, mice were infected with Leishmania major promastigotes. The result showed that immunization with pcDNA-mGMCSF-LdPxn1 elicited a mixed Th-1/Th-2 immune response with significantly higher production of IFN-γ than controls. Intracellular cytokine staining of antigen-stimulated spleen cells showed that immunization with this antigen elicited significantly higher proportion of CD4+ T cells that express IFN-γ, TNF-α, or IL-2. The antigen also induced significantly higher proportion of multipotent CD4+ cells that simultaneously express the three Th-1 cytokines. Moreover, a significant reduction in the footpad swelling was seen in mice immunized with pcDNA-mGMCSF-LdPxn1 antigen. Expression study in CHO cells demonstrated that pcDNA-mGMCSF-LdPxn-1 was expressed in mammalian system.

CONCLUSION

The result demonstrates that immunization of BALB/c mice with a plasmid expressing LdPxn1 in the presence of mGMCSF adjuvant elicits a strong specific immune response with high level induction of multipotent CD4+ cells that mediate protection of the mice from Leishmania major infection. To our knowledge, this is the first study showing the vaccine potential of Leishmania peroxidoxin -1.

Low concentrations of recombinant granulocyte macrophage-colony stimulating factor derived from Chinese hamster ovary cells augments long-term bioactivity with delayed clearance in vitro

To date, the biological activity of granulocyte macrophage-colony stimulating factor (GM-CSF) has been investigated by using mostly Escherichia coli- or yeast cell-derived recombinant human GM-CSF (erhGM-CSF and yrhGM-CSF, respectively). However, Chinese hamster ovary cell-derived recombinant human GM-CSF (crhGM-CSF), as well as natural human GM-CSF, is a distinct molecule that includes modifications by complicated oligosaccharide moieties. In the present study, we reevaluated the bioactivity of crhGM-CSF by comparing it with those of erhGM-CSF and yrhGM-CSF. The effect of short-term stimulation (0.5h) on the activation of neutrophils/monocytes or peripheral blood mononuclear cells (PBMCs) by crhGM-CSF was lower than those with erhGM-CSF or yrhGM-CSF at low concentrations (under 60pM). Intermediate-term stimulation (24h) among the different rhGM-CSFs with respect to its effect on the activation of TF-1 cells, a GM-CSF-dependent cell line, or PBMCs was not significantly different. In contrast, the proliferation/survival of TF-1 cells or PBMCs after long-term stimulation (72-168h) was higher at low concentrations of crhGM-CSF (15-30pM) than that of cells treated with other GM-CSFs. The proportion of apoptotic TF-1 cells after incubation with crhGM-CSF for 72h was lower than that of cells incubated with other rhGM-CSFs. These effects were attenuated by desialylation of crhGM-CSF. Clearance of crhGM-CSF but not desialylated-crhGM-CSF by both TF-1 cells and PBMCs was delayed compared with that of erhGM-CSF or yrhGM-CSF. These results suggest that sialylation of oligosaccharide moieties delayed the clearance of GM-CSF, thus eliciting increased long-term bioactivity in vitro.

GlycoDelete engineering of mammalian cells simplifies N-glycosylation of recombinant proteins

Heterogeneity in the N-glycans on therapeutic proteins causes difficulties for protein purification and process reproducibility and can lead to variable therapeutic efficacy. This heterogeneity arises from the multistep process of mammalian complex-type N-glycan synthesis. Here we report a glycoengineering strategy--which we call GlycoDelete--that shortens the Golgi N-glycosylation pathway in mammalian cells. This shortening results in the expression of proteins with small, sialylated trisaccharide N-glycans and reduced complexity compared to native mammalian cell glycoproteins. GlycoDelete engineering does not interfere with the functioning of N-glycans in protein folding, and the physiology of cells modified by GlycoDelete is similar to that of wild-type cells. A therapeutic human IgG expressed in GlycoDelete cells had properties, such as reduced initial clearance, that might be beneficial when the therapeutic goal is antigen neutralization. This strategy for reducing N-glycan heterogeneity on mammalian proteins could lead to more consistent performance of therapeutic proteins and modulation of biopharmaceutical functions.

Synthesis of granulocyte-macrophage colony-stimulating factor as homogeneous glycoforms and early comparisons with yeast cell-derived material

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a medicinally important glycoprotein, used as an immunostimulant following bone-marrow transplant. On the basis of reports of its potential utility as an anticancer vaccine adjuvant, we undertook to develop a synthetic route toward single-glycoform GM-CSF. We describe herein a convergent total synthesis of GM-CSF aglycone and two homogeneous glycoforms. Analytical and biological studies confirm the structure and activity of these synthetic congeners.

Effect of rice cell-derived human granulocyte-macrophage colony-stimulating factor on 5-fluorouracil-induced mucositis in hamsters

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important regulator of the maturation and function of cells in the granulocyte and macrophage lineages, and also plays a significant role in wound healing. In a previous study, we expressed human GM-CSF in rice cells (rice cell-derived human GM-CSF; rhGM-CSF). The purpose of the present study was to evaluate its effect on wound healing in oral mucositis. Oral mucositis was induced in Syrian hamster cheek pouches by 5-fluorouracil treatment and mechanical scratching. Ulcerated areas were treated from days 3 to 14 with an application of 200 µL saline, or of the same volume of a solution containing 0.04, 0.2, or 1 µg/mL rhGM-CSF. Treatment of hamsters with rhGM-CSF reduced the ulcerated areas of the oral mucosa, compared with the control. Early in the healing process, the mucositis tissue layer of the rhGM-CSF-treated group showed significantly decreased myeloperoxidase activity and increased numbers of proliferating cell nuclear antigen (PCNA)-positive cells. Treatment with rhGM-CSF also affected expression of inflammatory cytokines in the ulcerative mucosal tissue. These results demonstrate the efficacy of plant-produced rhGM-CSF in wound healing and have significant implications for the development of rhGM-CSF as a therapeutic agent for ulcerative oral mucositis.

Molecular cloning, sequencing and structural studies of granulocyte-macrophage colony-stimulating factor (GM-CSF) from Indian water buffalo (Bubalus bubalis)

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine that is essential for growth and development of progenitors of granulocytes and monocytes/macrophages. In this study, we report molecular cloning, sequencing and characterization of GM-CSF from Indian water buffalo, Bubalus bubalis. In addition, we performed sequence and structural analysis for buffalo GM-CSF. Buffalo GM-CSF has been compared with 17 mammalian GM-CSFs using multiple sequence alignment and phylogenetic tree. Three-dimensional model for buffalo GM-CSF and human receptor complex was built using homology modelling to study cross-reactivity between two species. Detailed analysis was performed to study GM-CSF interface and various interactions at the interface.

Chimeric HIV-1 envelope glycoproteins with potent intrinsic granulocyte-macrophage colony-stimulating factor (GM-CSF) activity

HIV-1 acquisition can be prevented by broadly neutralizing antibodies (BrNAbs) that target the envelope glycoprotein complex (Env). An ideal vaccine should therefore be able to induce BrNAbs that can provide immunity over a prolonged period of time, but the low intrinsic immunogenicity of HIV-1 Env makes the elicitation of such BrNAbs challenging. Co-stimulatory molecules can increase the immunogenicity of Env and we have engineered a soluble chimeric Env trimer with an embedded granulocyte-macrophage colony-stimulating factor (GM-CSF) domain. This chimeric molecule induced enhanced B and helper T cell responses in mice compared to Env without GM-CSF. We studied whether we could optimize the activity of the embedded GM-CSF as well as the antigenic structure of the Env component of the chimeric molecule. We assessed the effect of truncating GM-CSF, removing glycosylation-sites in GM-CSF, and adjusting the linker length between GM-CSF and Env. One of our designed Env(GM-CSF) chimeras improved GM-CSF-dependent cell proliferation by 6-fold, reaching the same activity as soluble recombinant GM-CSF. In addition, we incorporated GM-CSF into a cleavable Env trimer and found that insertion of GM-CSF did not compromise Env cleavage, while Env cleavage did not compromise GM-CSF activity. Importantly, these optimized Env(GM-CSF) proteins were able to differentiate human monocytes into cells with a macrophage-like phenotype. Chimeric Env(GM-CSF) should be useful for improving humoral immunity against HIV-1 and these studies should inform the design of other chimeric proteins.

A new generation of carbohydrate-based therapeutics: recombinant mucin-type fusion proteins as versatile inhibitors of protein-carbohydrate interactions

Cell surface carbohydrates are essential for a multitude of biomedically important interactions that take place at the cell surface. Carbohydrate-binding proteins are, therefore, significant targets for the development of carbohydrate-based inhibitors. Due to their multivalent character, monovalent low-molecular-weight sugar homologues or analogues are usually poor inhibitors of these interactions. Recent advances in organic and chemoenzymatic synthesis of carbohydrates will undoubtedly increase the pace by which new multivalent carbohydrate-based drugs are developed. Knowledge gained on the glycosyltransferases that are involved in glycan biosynthesis can be used to engineer host cells for recombinant production of proteins with tailored glycan substitution. In particular, recombinant mucin-type proteins can serve as natural scaffolds for multivalent presentation of therapeutic carbohydrate determinants.

Production and characterization of human granulocyte-macrophage colony-stimulating factor (hGM-CSF) expressed in the oleaginous yeast Yarrowia lipolytica

Since its isolation, the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) has been proposed as a new class of therapeutic biological products in the treatment of various diseases. However, the toxicity of this cytokine towards its expression host constitutes a major obstacle to bioprocess development for large-scale production. In this work, the optimized gene encoding hGM-CSF was expressed in the yeast Yarrowia lipolytica in one and two copies under the control of the fatty acid-inducible POX2 promoter. Protein secretion was directed by the targeting sequence of the extracellular lipase (LIP2): preXALip2. After 48 h of induction, Western blot analysis revealed the presence of a nonglycosylated form of 14.5 kDa and a trail of hGM-CSF hyperglycosylated varying from 23 kDa to more than 60 kDa. The two-copy transformants produced hGM-CSF level which was sevenfold higher compared to the single-copy ones. Deglycosylation with PNGase F showed two forms: a mature form of 14.5 kDa and an unprocessed form of 18 kDa. The addition of two alanines to the signal sequence resulted in correct hGM-CSF processing. The production level was estimated at 250 mg/l after preliminary optimization studies of the cultivation and induction phases. The purified hGM-CSF was identified by N-terminal sequencing and LC-MS/MS analysis; its biological activity was confirmed by stimulating the proliferation of TF1 cell line. This study demonstrated that Y. lipolytica is a promising host for the efficient production of active toxic proteins like hGM-CSF.

Ion mobility mass spectrometry for extracting spectra of N-glycans directly from incubation mixtures following glycan release: application to glycans from engineered glycoforms of intact, folded HIV gp120

The analysis of glycosylation from native biological sources is often frustrated by the low abundances of available material. Here, ion mobility combined with electrospray ionization mass spectrometry have been used to extract the spectra of N-glycans released with PNGase F from a serial titration of recombinantly expressed envelope glycoprotein, gp120, from the human immunodeficiency virus (HIV). Analysis was also performed on gp120 expressed in the α-mannosidase inhibitor, and in a matched mammalian cell line deficient in GlcNAc transferase I. Without ion mobility separation, ESI spectra frequently contained no observable ions from the glycans whereas ions from other compounds such as detergents and residual buffer salts were abundant. After ion mobility separation on a Waters T-wave ion mobility mass spectrometer, the N-glycans fell into a unique region of the ion mobility/m/z plot allowing their profiles to be extracted with good signal:noise ratios. This method allowed N-glycan profiles to be extracted from crude incubation mixtures with no clean-up even in the presence of surfactants such as NP40. Furthermore, this technique allowed clear profiles to be obtained from sub-microgram amounts of glycoprotein. Glycan profiles were similar to those generated by MALDI-TOF MS although they were more susceptible to double charging and fragmentation. Structural analysis could be accomplished by MS/MS experiments in either positive or negative ion mode but negative ion mode gave the most informative spectra and provided a reliable approach to the analysis of glycans from small amounts of glycoprotein.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Temperature Reduction in Cultures of hGM-CSF-expressing CHO Cells: Effect on Productivity and Product Quality

We have demonstrated that temperature reduction from 37 to 33 degrees C in the culture of a CHO cell line producing recombinant human granulocyte macrophage colony stimulating factor (CHO-K1-hGM-CSF) leads to a reduced growth rate, increased cell viability, improved cellular productivity, and decreased cell metabolism. In the present study, CHO-K1-hGM-CSF cells were cultured in a biphasic mode: first, a 37 degrees C growth phase for achieving a high cell number, followed by a production phase where the culture temperature was shifted to 33 degrees C. The maximum cell density was not affected after temperature reduction while cell viability remained above 80% for a further 3.7 days in the culture kept at the lower temperature, when compared to the control culture maintained at 37 degrees C. Furthermore, the total rhGM-CSF production increased 6 times in the culture shifted to 33 degrees C. Because the quality and hence the in vivo efficacy of a recombinant protein might be affected by numerous factors, we have analyzed the N- and O-glycosylation of the protein produced under both cell culture conditions using high-pH anion-exchange chromatography and complementary mass spectrometry techniques. The product quality data obtained from the purified protein preparations indicated that decreasing temperature had no significant effect on the rhGM-CSF glycosylation profiles, including the degree of terminal sialylation. Moreover, both preparations exhibited the same specific in vitro biological activity. These results revealed that the employed strategy had a positive effect on the cell specific productivity of CHO-K1-hGM-CSF cells without affecting product quality, representing a novel procedure for the rhGM-CSF production process.

Metalloproteinases Shed TREM-1 Ectodomain from Lipopolysaccharide-Stimulated Human Monocytes

Triggering receptors expressed on myeloid cell (TREM) proteins are a family of cell surface receptors that participate in diverse cellular processes such as inflammation, coagulation, and bone homeostasis. TREM-1, in particular, is expressed on neutrophils and monocytes and is a potent amplifier of inflammatory responses. LPS and other microbial products induce up-regulation of cell surface-localized TREM-1 and the release of its soluble form, sTREM-1. Two hypotheses have been advanced to explain the origin of sTREM-1: alternative splicing of TREM-1 mRNA and proteolytic cleavage(s) of mature, membrane-anchored TREM-1. In this report, we present conclusive evidence in favor of the proteolytic mechanism of sTREM-1 generation. No alternative splicing forms of TREM-1 were detected in monocytes/macrophages. Besides, metalloproteinase inhibitors increased the stability of TREM-1 at the cell surface while significantly reducing sTREM-1 release in cultures of LPS-challenged human monocytes and neutrophils. We conclude that metalloproteinases are responsible for shedding of the TREM-1 ectodomain through proteolytic cleavage of its long juxtamembrane linker.

Comparative studies on the analysis of urinary trypsin inhibitor (ulinastatin) preparations

Urinary trypsin inhibitor (ulinastatin) is a characteristic protein pharmaceutical which contains both glycosaminoglycans and N-linked glycans in its molecule and has been used for treatment of acute pancreatitis. The comparability of ulinastatin preparations of different lots or from different companies was studied by using conventional analytical approaches such as SDS-PAGE, cellulose acetate membrane electrophoresis, and HP size-exclusion chromatography (SEC) and also by using newly developed techniques such as CE and MALDI-TOF MS. The methods using SEC and SDS-PAGE according to The Japanese Pharmacopoeia showed similar molecular masses for two different preparations, and the estimated molecular masses were significantly different from those observed with MALDI-TOF MS. We also showed that the electrophoretic methods using cellulose acetate membrane electrophoresis and CE can be used for comparability assessments of ulinastatin preparations. In addition, we analyzed the unsaturated disaccharides derived from glycosaminoglycan (chondroitin 4-sulfate chain) and N-linked oligosaccharides attached to ulinastatin by CE after releasing them by enzymatic digestion followed by fluorescent labeling with 2-aminoacridone and 2-aminobenzoic acid, respectively. The results indicated that carbohydrate chains are important as markers for comparability assessments of ulinastatin pharmaceutical preparations.

GlycoPEGylation of recombinant therapeutic proteins produced in Escherichia coli

Covalent attachment of polyethylene glycol, PEGylation, has been shown to prolong the half-life and enhance the pharmacodynamics of therapeutic proteins. Current methods for PEGylation, which rely on chemical conjugation through reactive groups on amino acids, often generate isoforms in which PEG is attached at sites that interfere with bioactivity. Here, we present a novel strategy for site-directed PEGylation using glycosyltransferases to attach PEG to O-glycans. The process involves enzymatic GalNAc glycosylation at specific serine and threonine residues in proteins expressed without glycosylation in Escherichia coli, followed by enzymatic transfer of sialic acid conjugated with PEG to the introduced GalNAc residues. The strategy was applied to three therapeutic polypeptides, granulocyte colony stimulating factor (G-CSF), interferon-alpha2b (IFN-alpha2b), and granulocyte/macrophage colony stimulating factor (GM-CSF), which are currently in clinical use.

Identification of a protein from rust fungi transferred from haustoria into infected plant cells

The formation of haustoria is one of the hallmarks of the interaction of obligate biotrophic fungi with their host plants. In addition to their role in nutrient uptake, it is hypothesized that haustoria are actively involved in establishing and maintaining the biotrophic relationship. We have identified a 24.3-kDa protein that exhibited a very unusual allocation. Rust transferred protein 1 from Uromyces fabae (Uf-RTP1p) was not only detected in the host parasite interface, the extrahaustorial matrix, but also inside infected plant cells by immunofluorescence and electron microscopy. Uf-RTP1p does not exhibit any similarity to sequences currently listed in the public databases. However, we identified a homolog of Uf-RTP1p in the related rust fungus Uromyces striatus (Us-RTP1p). The localization of Uf-RTP1p and Us-RTP1p inside infected plant cells was confirmed, using four independently raised polyclonal antibodies. Depending on the developmental stage of haustoria, Uf-RTP1p was found in increasing amounts in host cells, including the host nucleus. Putative nuclear localization signals (NLS) were found in the predicted RTP1p sequences. However, functional efficiency could only be verified for the Uf-RTP1p NLS by means of green fluorescent protein fusions in transformed tobacco protoplasts. Western blot analysis indicated that Uf-RTP1p and Us-RTP1p most likely enter the host cell as N-glycosylated proteins. However, the mechanism by which they cross the extrahaustorial membrane and accumulate in the host cytoplasm is unknown. The localization of RTP1p suggests that it might play an important role in the maintenance of the biotrophic interaction.

Structural analysis of a novel anionic polysaccharide fromPorphyromonas gingivalisstrain W50 related to Arg-gingipain glycans

The Arg-gingipains (RgpsA and B) of Porphyromonas gingivalis are a family of extracellular cysteine proteases and are important virulence determinants of this periodontal bacterium. A monoclonal antibody, MAb1B5, which recognizes an epitope on glycosylated monomeric RgpAs also cross-reacts with a cell-surface polysaccharide of P. gingivalis W50 suggesting that the maturation pathway of the Arg-gingipains may be linked to the biosynthesis of a surface carbohydrate. We report the purification and structural characterization of the cross-reacting anionic polysaccharide (APS), which is distinct from both the lipopolysaccharide and serotype capsule polysaccharide of P. gingivalis W50. The structure of APS was determined by 1D and 2D NMR spectroscopy and methylation analysis, which showed it to be a phosphorylated branched mannan. The backbone is built up of alpha-1,6-linked mannose residues and the side-chains contain alpha-1,2-linked mannose oligosaccharides of different lengths (one to two sugar residues) attached to the backbone via 1,2-linkage. One of the side-chains in the repeating unit contains Manalpha1-2Manalpha1-phosphate linked via phosphorus to a backbone mannose at position 2. De-O-phosphorylation of APS abolished cross-reactivity suggesting that Manalpha1-2Manalpha1-phosphate fragment forms part of the epitope recognized by MAb1B5. This phosphorylated branched mannan represents a novel polysaccharide that is immunologically related to the post-translational additions of Arg-gingipains.