Differential N-glycosylation of a monoclonal antibody expressed in tobacco leaves with and without endoplasmic reticulum retention signal apparently induces similar in vivo stability in mice

Plant cells are able to perform most of the post-translational modifications that are required by recombinant proteins to achieve adequate bioactivity and pharmacokinetics. However, regarding N-glycosylation the processing of plant N-glycans in the Golgi apparatus displays major differences when compared with that of mammalian cells. These differences in N-glycosylation are expected to influence serum clearance rate of plant-derived monoclonal antibodies. The monoclonal antibody against the hepatitis B virus surface antigen expressed in Nicotiana tabacum leaves without KDEL endoplasmic reticulum (ER) retention signal (CB.Hep1(-)KDEL) and with a KDEL (Lys-Asp-Glu-Leu) fused to both IgG light and heavy chains (CB.Hep1(+)KDEL) were tested for in vivo stability in mice. Full characterization of N-glycosylation and aggregate formation in each monoclonal antibody batch was determined. The mouse counterpart (CB.Hep1) was used as control. Both (CB.Hep1(-)KDEL) and (CB.Hep1(+)KDEL) showed a faster initial clearance rate (first 24 h) compared with the analogous murine antibody while the terminal phase was similar in the three antibodies. Despite the differences between CB.Hep1(+)KDEL and CB.Hep1(-)KDEL N-glycans, the in vivo elimination in mice was indistinguishable from each other and higher than the murine monoclonal antibody. Molecular modelling confirmed that N-glycans linked to plantibodies were oriented away from the interdomain region, increasing the accessibility of the potential glycan epitopes by glycoprotein receptors that might be responsible for the difference in stability of these molecules.

Chemical and enzymatic N-glycan release comparison for N-glycan profiling of monoclonal antibodies expressed in plants

Plants synthesize N-glycans containing the antigenic sugars alpha(1,3)-fucose and beta(1,2)-xylose. Therefore it is important to monitor these N-glycans in monoclonal antibodies produced in plants (plantibodies). We evaluated several techniques to characterize the N-glycosylation of a plantibody produced in tobacco plants with and without the KDEL tetrapeptide endoplasmic reticulum retention signal which should inhibit or drastically reduce the addition of alpha(1,3)-fucose and beta(1,2)-xylose. Ammonium hydroxide/carbonate-based chemical deglycosylation and PNGase A enzymatic release were investigated giving similar 2-aminobenzamide-labeled N-glycan HPLC profiles. The chemical release does not generate peptides which is convenient for MS analysis of unlabeled pool but its main drawback is that it induces degradation of alpha1,3-fucosylated N-glycan reducing terminal sugar. Three analytical methods for N-glycan characterization were evaluated: (i) MALDI-MS of glycopeptides from tryptic digestion; (ii) negative-ion ESI-MS/MS of released N-glycans; (iii) normal-phase HPLC of fluorescently labeled glycans in combination with exoglycosidase sequencing. The MS methods identified the major glycans, but the HPLC method was best for identification and relative quantitation of N-glycans. Negative-mode ESI-MS/MS permitted also the correct identification of the linkage position of the fucose residue linked to the inner core N-acteylglucosamine (GlcNAc) in complex N-glycans.

N-glycosylation of plant recombinant pharmaceuticals

N-glycosylation is a maturation event necessary for the correct function, efficiency, and stability of a high number of biopharmaceuticals. This chapter presented here proposes various methods to determine whether, how, and where a plant pharmaceutical is N-glycosylated. These methods rely on blot detection with glycan-specific probes, specific deglycosylation of glycoproteins followed by mass spectrometry, N-glycan profile analysis, and glycopeptide identification by LC-MS.

Plant N-glycan profiling of minute amounts of material

Development of convenient strategies for identification of plant N-glycan profiles has been driven by the emergence of plants as an expression system for therapeutic proteins. In this article, we reinvestigated qualitative and quantitative aspects of plant N-glycan profiling. The extraction of plant proteins through a phenol/ammonium acetate procedure followed by deglycosylation with peptide N-glycosidase A (PNGase A) and coupling to 2-aminobenzamide provides an oligosaccharide preparation containing reduced amounts of contaminants from plant cell wall polysaccharides. Such a preparation was also suitable for accurate qualitative and quantitative evaluation of the N-glycan content by mass spectrometry. Combining these approaches allows the profiling to be carried out from as low as 500 mg of fresh leaf material. We also demonstrated that collision-induced dissociation (CID) mass spectrometry in negative mode of N-glycans harboring alpha(1,3)- or alpha(1,6)-fucose residue on the proximal GlcNAc leads to specific fragmentation patterns, thereby allowing the discrimination of plant N-glycans from those arising from mammalian contamination.

The goat mammary glandular epithelial (GMGE) cell line promotes polyfucosylation and N,N′-diacetyllactosediaminylation of N-glycans linked to recombinant human erythropoietin

We have established a continuous, non-transformed cell line from primary cultures from Capra hircus mammary gland. Low-density cultures showed a homogeneous epithelial morphology without detectable fibroblastic or myoepithelial cells. The culture was responsive to contact inhibition of proliferation and its doubling time was dependent on the presence of insulin and epidermal growth factor (EGF). GMGE cells secrete caseins regardless of the presence or absence of lactogenic hormones in the culture media. Investigation of the total N-glycan pool of human erythropoietin (rhEPO) expressed in GMGE cells by monosaccharide analysis, HPLC profiling, and mass spectrometry, indicated significant differences with respect to the same protein expressed in Chinese hamster ovary (CHO) cells. N-Glycans of rhEPO-GMGE are core-fucosylated, but fucosylation of outer arms was also found. Our results also revealed the presence of low levels of sialylation (>95% Neu5Ac), N,N'-diacetyllactosediamine units, and possibly Gal-Gal non-reducing terminal elements.

Analytical strategies to investigate plant N-glycan profiles in the context of plant-made pharmaceuticals

Plants are attractive hosts for the production of recombinant proteins. However, their inability to process authentic human N-glycan structures imposes a major limitation on their use as expression systems for therapeutic products. Several strategies have emerged to engineer plant N-glycans into human-compatible molecules. In this context, fast and reliable analytical strategies for the identification of plant N-glycan profiles have been developed to define the N-glycosylation pathways of crops, to monitor the production of plant-made pharmaceuticals and to assess in planta remodelling strategies.

High expression level of recombinant human erythropoietin in the milk of non-transgenic goats

The high degree of structural conservation of erythropoietin between species, make it, especially, difficult to produce this protein growth factor in the milk of transgenic animals. Here, we show that through the direct transduction of the mammary epithelium, it is possible to produce high levels of recombinant human erythropoietin in the milk of non-transgenic goats without causing harm to the animals. The efficiency of viral transduction was improved through a temporal disruption of tight-junctions with EGTA allowing for the expression of human erythropoietin at levels of up to 2g/L in milk. The human erythropoietin was purified from the milk using a multi-step protocol involving milk clarification, two precipitation steps and two affinity chromatographies, with a yield of about 70% and purity over 98%. However, the human erythropoietin expressed in milk was underglycosylated, which seems to be the main cause for its low in vivo hematopoietic activity. Nonetheless, these results demonstrate that through the direct transduction of the mammary epithelium it is possible to produce potentially toxic proteins in milk, at levels high enough for their purification and biological characterization.

Plant-derived mouse IgG monoclonal antibody fused to KDEL endoplasmic reticulum-retention signal is N-glycosylated homogeneously throughout the plant with mostly high-mannose-type N-glycans

Plants are potential hosts for the expression of recombinant glycoproteins intended for therapeutic purposes. However, N-glycans of mammalian glycoproteins produced in transgenic plants differ from their natural counterparts. The use of the endoplasmic reticulum (ER)-retention signal has been proposed to restrict glycosylation of plantibodies to only high-mannose-type N-glycans. Furthermore, little is known about the influence of plant development and growth conditions on N-linked glycosylation. Here, we report a detailed N-glycosylation profiling study of CB.Hep1, a mouse IgG2b monoclonal antibody (mAb) against hepatitis B surface antigen (HBsAg) currently expressed in tobacco plants (Nicotiana tabacum L.). The KDEL ER-retention signal was fused to the C-terminal of both light and heavy chains. The structures of the N-linked glycans of this mAb produced in transgenic tobacco plants at various growth stages were analysed by high-performance liquid chromatography (HPLC) profiling techniques and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and compared with those of murine origin. The high-mannose-type oligosaccharides accounted for more than 80% of the total N-glycans, with Man7GlcNAc2 being the most abundant species. Some complex N-glycans bearing xylose and small amounts of oligosaccharides with both xylose and fucose were identified. No appreciable differences were detected when comparing glycosylation at different leaf ages, e.g. from seedling leaves up to 8 weeks old and top or basal leaves of mature plants, or between leaves, stems and whole plants. A strict retention of glycoproteins to ER by the use of the tetrapeptide KDEL was not sufficient, even though the majority of the resulting N-glycosylation was of the high-mannose type. It is highly likely to be dependent on other factors, which are most probably protein specific.

Differential in vitro and in vivo glycosylation of human erythropoietin expressed in adenovirally transduced mouse mammary epithelial cells

The expression of human erythropoietin in the mammary gland is an attractive approach to diminish its current production cost. Previous attempts to produce erythropoietin in the milk of transgenic animals resulted in very low expression levels and in a detrimental effect in the health of the founder animals. Here, we show that the direct transduction of the mouse mammary gland with an adenoviral vector carrying the cDNA of erythropoietin promotes its expression in milk at a level as high as 3.5 mg/ml. The recombinant erythropoietin derived from mouse milk showed a different migration and distribution after SDS-PAGE electrophoresis as well as a low in vivo hematopoietic activity. Enzymatic deglycosylation showed that these molecular weight disparities are in part due to differential glycosylation compared to with its counterpart produced in CHO and HC11 cell lines. The difference between in vivo and in vitro glycosylation of human erythropoietin expressed in adenovirally transduced mammary epithelial cells suggests that key enzymes in the glycosylation pathway may be insufficient during lactation. Thus, the direct transduction of the mammary epithelium seems to be a powerful tool to express toxic proteins in milk at levels high enough for their physical, chemical and biological characterization before undertaking the generation of a transgenic mammal.

An integral approach towards a practical application for a plant-made monoclonal antibody in vaccine purification

The use of transgenic plants for the production of pharmaceutical compounds has received increasing attention in the last few years. However, many technological and regulatory issues regarding the practical exploitation of this alternative system of production remain to be solved; a situation that explains the lack of commercial products derived from such a system. This paper reports the expression in transgenic plants and cells of a single-chain antibody variable-region fragment (scFv) and a mouse monoclonal antibody to the hepatitis B virus surface antigen (HBsAg). The large-scale purification of the scFv from plants and its use for immunopurification of HBsAg are also described, together with elements concerning regulatory issues and technologies for compliance with good manufacturing and agricultural practices.

Influence of culture conditions on the N-glycosylation of a monoclonal antibody specific for recombinant hepatitis B surface antigen

MAbs (monoclonal antibodies) are becoming increasingly important as diagnostic tools for pharmaceutical biotechnology, and hence it is crucial that they are produced under controlled conditions to assure their consistency and reproducibility, not only in terms of protein sequence and bioactivity, but also in terms of post-translational modifications, e.g. for N-glycosylation. Hybridoma CB.Hep-1, which secretes an IgG2b mAb, was cultured in vivo in ascites and in vitro in static-flask, spinner-flask, dialysis-membrane and perfusion systems using protein-free, low-serum-containing medium (1% foetal-calf serum) and high-serum-containing medium (8% foetal-calf serum). These CB.Hep-1 mAbs were fully characterized, and insignificant differences in the affinity constant were observed. Glycosylation profiling was performed by labelling the N-glycans released by peptide N-glycosidase F with either of the fluorophore tags 8-aminonaphthalene-1,3,6-trisulphonic acid and 4-aminobenzoic acid. The mAb produced in vivo showed two major biantennary-complex-type N-glycans: monogalactosylated, core-fucosylated and agalactosylated, core-fucosylated. The mAbs produced in vitro in static flasks and spinner flasks were not significantly influenced by the serum content in the culture media and showed a higher degree of N-glycan galactosylation compared with those produced in mouse-ascites, hollow-fibre and membrane systems. The monogalactosylated, core-fucosylated structure was the most abundant N-glycan except for those produced in ascites and hollow fibres, where the agalactosylated, core-fucosylated glycoform was the major specie. MAbs produced in high-cellular-yield systems displayed greater galactosylation heterogeneity influenced by changes in culture media.

The cattle tick antigen, Bm95, expressed in Pichia pastoris contains short chains of N- and O-glycans

Bm95 is an antigen isolated from Boophilus microplus strains with low susceptibility to antibodies developed in cattle vaccinated with the recombinant Bm86 antigen (Gavac, HeberBiotec S.A., Cuba). It is a Bm86-like surface protein, which by similarity contains seven EGF-like domains and a lipid-binding GPI-anchor site at the C-terminal region. The primary structure of the recombinant (rBm95) protein expressed in Pichia pastoris was completely verified by LC/MS. The four potential glycosylation sites (Asn 122, 163, 329, and 363) are glycosylated partially with short N-glycans, from Man(5)GlcNAc(2) to Man(9)GlcNAc(2) of which, Man(8-9)GlcNAc(2) were the most abundant. O-Glycopeptides are distributed mostly towards the protein N-terminus. While the first N-glycosylated site (Asn(122)) is located between EGF-like domains 2 and 3, where the O-glycopeptides were found, two other N-glycosylated sites (Asn(329) and Asn(363)) are located between EGF-like domains 5 and 6, a region devoid of O-glycosylated Ser or Thr.

Hypogalactosylation of serum IgG in patients with coeliac disease

Coeliac disease (CD) is described as an autoimmune enteropathy associated with the presence of IgG and IgA antigliadin and antitransglutaminase autoantibodies. While of diagnostic significance, the role of these autoantibodies in the immunopathogenesis of CD is elucidated. An inappropriate T cell immune response to gluten is also involved in the pathogenesis of CD, as evidenced by autoantibody switching. The N-glycans released from serum IgG of CD patients and three groups of healthy controls, of differing age ranges, were analysed by NH2-high performance liquid chromatography (HPLC). The fucosylated biantennary N- glycans were the most abundant neutral oligosaccharides; in particular, the agalacto form (G0F) showed a mean value of 42% (s.d. +/- 7.4), 30% (s.d. +/- 5.9), 26% (s.d. +/- 4.2) and 35% (s.d. +/- 6.8) for CD patients, healthy children, healthy adults under 40 and healthy adults over 40 years old, respectively. The ratio of asialo agalacto fucosylated biantenna to asialo monogalacto fucosylated biantenna (G0F)/(G1F) for CD patients showed a significant increase compared to healthy children (P < 0.0002), healthy adults under 40 (P < 0.0002) and healthy adults over 40 years old (P < 0.01). Hypogalactosylation was more pronounced for CD patients than for the patients with other autoimmune diseases such as rheumatoid arthritis or psoriatic arthritis.

Dextranase (alpha-1,6 glucan-6-glucanohydrolase) from Penicillium minioluteum expressed in Pichia pastoris: two host cells with minor differences in N-glycosylation

Differences in glycosylation between the natural alpha-1,6 glucan-6-glucanohydrolase from Penicillium minioluteum and the heterologous protein expressed in the yeast Pichia pastoris were analyzed. Glycosylation profiling was carried out using fluorophore-assisted carbohydrate electrophoresis and amine absorption high-performance liquid chromatography (NH(2)-HPLC) in combination with matrix-assisted laser desorption-time of flight-mass spectrometry. Both microorganisms produce only oligomannosidic type structures, but the oligosaccharide population differs in both enzymes. The native enzyme has mainly short oligosaccharide chains ranging from Man(5)GlcNAc(2) to Man(9)GlcNAc(2), of which Man(8)GlcNAc(2) was the most represented oligosaccharide. The oligosaccharides linked to the protein produced in P. pastoris range from Man(7)GlcNAc(2) up to Man(14)GlcNAc(2), with Man(8)GlcNAc(2) and Man(9)GlcNAc(2) being the most abundant structures. In both enzymes the first glycosylation site (Asn(5)) is always glycosylated. However, Asn(537) and Asn(540) are only partially glycosylated in an alternate manner.

Characterization of protein glycoforms with N-linked neutral and phosphorylated oligosaccharides: studies on the glycosylation of endoglucanase 1 (Cel7B) from Trichoderma reesei

Using anion-exchange chromatography the catalyticdomain of endoglucanase 1 (Cel7B) from Trichoderma reesei was resolved in multiple fractions with different isoelectric points, presumably related to different glycoforms of the enzyme. The protein fractions were analysed using lectins and electrospray MS. Isolated N-glycans were analysed by fluorophore-assisted carbohydrate electrophoresis and amine-adsorption HPLC. The results show that this particular preparation contained at least 14 different glycoforms. The major isoform contained only one GlcNAc, presumably N-linked, and one mannose, most probably O-linked to serine/threonine at a separate site. Except for a small population containing Man(5)GlcNAc(2)+1-2 Man, the rest of the protein had negatively charged phosphate-containing N-glycans. All glycoforms contained at least one O-linked mannose residue. The increased negative charge of the protein, introduced by oligosaccharide phosphorylation, is the most probable reason for the different isoelectric points and the occurrence of multiple peaks during purification.

Characterization of the oligosaccharides assembled on the Pichia pastoris-expressed recombinant aspartic protease

Aspartic protease, widely used as a milk-coagulating agent in industrial cheese production, contains three potential N-glycosylation sites. In this study, we report the characterization of N-linked oligosaccharides on recombinant aspartic protease secreted from the methylotrophic yeast Pichia pastoris using a combination of mass spectrometric, 2D chromatographic, chemical and enzymatic methods. The carbohydrates from site I (Asn79) were found to range from Man6-17GlcNAc2 with 50% bearing a phospho-diester-motif, site II (Asn113) was not occupied and site III (Asn188) contained mostly uncharged species ranging from Man-13GlcNAc2. These charged groups are not affecting the transport through the secretion pathway of the recombinant glycoprotein. Changes from a molasses-based medium to a minimal salts-based medium led to a clear reduction of the degree of phosphorylation of the N-glycan population.

Variation in N-linked oligosaccharide structures on heterologous proteins secreted by the methylotrophic yeast Pichia pastoris

We report the characterization of N-linked oligosaccharides on six foreign glycoproteins secreted from the methylotrophic yeast Pichia pastoris. These proteins included: a bacterial enzyme, Bacillus licheniformis alpha-amylase; three fungal enzymes, Saccharomyces cerevisiae invertase, Penicillium minioluteum dextranase, and Mucor pusillus aspartic protease; and two higher eukaryotic proteins, Boophilus microplus (tick) gut antigen and bovine enterokinase catalytic subunit. The carbohydrates on these proteins were observed to vary in size, with Man8GlcNAc2 and Man9GlcNAc2 structures being the most frequently observed species. Substantial amounts of shorter oligomannoside structures were present only on invertase, and longer structures (up to Man18GlcNAc2) were common on aspartic protease and enterokinase. Phosphorylated oligosaccharides were observed on one protein, aspartic protease. Unlike oligosaccharides on glycoproteins secreted from S. cerevisiae, no terminal alpha1,3-linked mannosylation was observed on any of the six P. pastoris-secreted proteins. Changing the growth and induction medium from a minimal salt-based medium to a molasses-based medium had little effect on the size of the oligomannosides. From these results, it is apparent that most foreign proteins secreted from P. pastoris are not subjected to the extensive mannosylation (hyperglycosylation) that commonly occurs in proteins secreted from S. cerevisiae.

Two-dimensional mapping of 8-amine-1,3,6-naphthalene trisulfonic acid derivatives of N-linked neutral and sialyloligosaccharides

We describe a simple and sensitive two-dimensional sugar-mapping technique of 8-amine-1,3,6-naphthalene trisulfonic acid derivatives (ANTS derivatives) of neutral and sialyloligosaccharides for structure analysis and characterization of N-linked oligosaccharides using picomoles of samples. The method includes: (1) reductive amination with ANTS of enzymatically released oligosaccharides, (2) simultaneous separation of oligosaccharide derivatives in a fluorophore-assisted carbohydrate electrophoresis and NH2-HPLC column under ion suppression conditions, (3) plotting of the relative migration indexes (X axis) and relative retention times (Y axis), and (4) when necessary, additional exoglycosidase digestion. As illustrated by the glycosylation profiling and structural analysis of alpha 1 anti-trypsin and murine IgG 2a, this methodology fulfills most of the requirements for a complete characterization of neutral and charged oligosaccharides released from N-glycosylated glycoprotein.

Purification and characterization of an invertase from Candida utilis: comparison with natural and recombinant yeast invertases

A periplasmic invertase from the yeast Candida utilis was purified to homogeneity from cells fully derepressed for invertase synthesis. The enzyme was purified by successive Sephacryl S-300, and affinity chromatography and shown to be a dimeric glycoprotein composed of two identical monomer subunits with an apparent molecular mass of 150 kDa. After EndoH treatment, the deglycosylated protein showed an apparent molecular weight of 60 kDa. The apparent K(m) values for sucrose and raffinose were 11 and 150 mM, respectively, similar to those reported in Saccharomyces cerevisiae. The range of optimum temperature was 60-75 degrees C. The optimum pH was 5.5 and the enzyme was stable over pH range 3-6.

Concanavalin A- and wheat germ agglutinin-conjugated lectins as a tool for the identification of multiple N-glycosylation sites in heterologous protein expressed in yeast

We report here a methodology that allows the identification of glycosylation sites by a combination of protein enzymatic digestion, glycopeptide separation on a reverse-phase HPLC column, and further recognition in a dot-blot system using concanavalin A-horseradish peroxidase. Wheat germ agglutinin-horseradish peroxidase is used as the recognition system for peptides generated after proteolytic digestion of endoglycosidase H deglycosylated protein. Glycosylation sites were confirmed by automatic Edman degradation and fast atom bombardment mass spectrometry. This methodology was applied to a model glycoprotein, alpha-amylase from Bacillus licheniformis, which is unglycosylated in its natural host and appears highly glycosylated when expressed in the methylotrophic yeast Pichia pastoris.