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

Thermoascus aurantiacus harbors an esterase/lipase that is highly activated by anionic surfactant

Fungal lipolytic enzymes play crucial roles in various lipid bio-industry processes. Here, we elucidated the biochemical and structural characteristics of an unexplored fungal lipolytic enzyme (TaLip) from Thermoascus aurantiacus var. levisporus, a strain renowned for its significant industrial relevance in carbohydrate-active enzyme production. TaLip belongs to a poorly understood phylogenetic branch within the class 3 lipase family and prefers to hydrolyze mainly short-chain esters. Nonetheless, it also displays activity against natural long-chain triacylglycerols. Furthermore, our analyses revealed that the surfactant sodium dodecyl sulfate (SDS) enhances the hydrolytic activity of TaLip on pNP butyrate by up to 5.0-fold. Biophysical studies suggest that interactions with SDS may prevent TaLip aggregation, thereby preserving the integrity and stability of its monomeric form and improving its performance. These findings highlight the resilience of TaLip as a lipolytic enzyme capable of functioning in tandem with surfactants, offering an intriguing enzymatic model for further exploration of surfactant tolerance and activation in biotechnological applications.

Strategic approaches for designing yeast strains as protein secretion and display platforms

Yeast has been established as a versatile platform for expressing functional molecules, owing to its well-characterized biology and extensive genetic modification tools. Compared to prokaryotic systems, yeast possesses advanced cellular mechanisms that ensure accurate protein folding and post-translational modifications. These capabilities are particularly advantageous for the expression of human-derived functional proteins. However, designing yeast strains as an expression platform for proteins requires the integration of molecular and cellular functions. By delving into the complexities of yeast-based expression systems, this review aims to empower researchers with the knowledge to fully exploit yeast as a functional platform to produce a diverse range of proteins. This review includes an exploration of the host strains, gene cassette structures, as well as considerations for maximizing the efficiency of the expression system. Through this in-depth analysis, the review anticipates stimulating further innovation in the field of yeast biotechnology and protein engineering.

Characterization of recombinant human lactoferrin expressed in Komagataella phaffii

This work presents a thorough characterization of Helaina recombinant human lactoferrin (rhLF, Effera™) expressed in a yeast system at an industrial scale for the first time. Proteomic analysis confirmed that its amino acid sequence is identical to that of native human LF. N-linked glycans were detected at three known glycosylation sites, namely, Asparagines-156, -497, and -642 and they were predominantly oligomannose structures having five to nine mannoses. Helaina rhLF's protein secondary structure was nearly identical to that of human milk lactoferrin (hmLF), as revealed by microfluidic modulation spectroscopy. Results of small-angle X-ray scattering (SAXS) and analytical ultracentrifugation analyses confirmed that, like hmLF, Helaina rhLF displayed well-folded globular structures in solution. Reconstructed solvent envelopes of Helaina rhLF, obtained through the SAXS analysis, demonstrated a remarkable fit with the reported crystalline structure of iron-bound native hmLF. Differential scanning calorimetry investigations into the thermal stability of Helaina rhLF revealed two distinct denaturation temperatures at 68.7 ± 0.9 °C and 91.9 ± 0.5 °C, consistently mirroring denaturation temperatures observed for apo- and holo-hmLF. Overall, Helaina rhLF differed from hmLF in the N-glycans they possessed; nevertheless, the characterization results affirmed that Helaina rhLF was of high purity and exhibited globular structures closely akin to that of hmLF.

Escherichia coli and Pichia pastoris: microbial cell-factory platform for -full-length IgG production

Owing to the unmet demand, the pharmaceutical industry is investigating an alternative host to mammalian cells to produce antibodies for a variety of therapeutic and research applications. Regardless of some disadvantages, Escherichia coli and Pichia pastoris are the preferred microbial hosts for antibody production. Despite the fact that the production of full-length antibodies has been successfully demonstrated in E. coli, which has mostly been used to produce antibody fragments, such as: antigen-binding fragments (Fab), single-chain fragment variable (scFv), and nanobodies. In contrast, Pichia, a eukaryotic microbial host, is mostly used to produce glycosylated full-length antibodies, though hypermannosylated glycan is a major challenge. Advanced strategies, such as the introduction of human-like glycosylation in endotoxin-edited E. coli and cell-free system-based glycosylation, are making progress in creating human-like glycosylation profiles of antibodies in these microbes. This review begins by explaining the structural and functional requirements of antibodies and continues by describing and analyzing the potential of E. coli and P. pastoris as hosts for providing a favorable environment to create a fully functional antibody. In addition, authors compare these microbes on certain features and predict their future in antibody production. Briefly, this review analyzes, compares, and highlights E. coli and P. pastoris as potential hosts for antibody production.

Predicted N-terminal N-linked glycosylation sites may underlie membrane protein expression patterns in Saccharomyces cerevisiae

N-linked glycosylation is one type of posttranslational modification that proteins undergo during expression. The following describes the effects of N-linked glycosylation on high-level membrane protein expression in yeast with an emphasis on Saccharomyces cerevisiae. N-linked glycosylation is highlighted here as an important consideration when preparing membrane protein gene constructs for expression in S. cerevisiae, which continues to be used as a workhorse in both research and industrial applications. Non-native N-linked glycosylation commonly occurs during the heterologous expression of mammalian proteins in many yeast species which can have important immunological consequences when used in the production of biotherapeutic proteins or peptides. Further, non-native N-linked glycosylation can lead to improper protein folding and premature degradation, which can impede high-level expression yields and hinder downstream analysis. Multiple strategies are presented in this article, which suggest different methods that can be implemented to circumvent the unwanted consequences of N-linked glycosylation during the expression process. These considerations may have long-term benefits for high-level protein production in S. cerevisiae across a broad spectrum of expression targets with special emphasis placed on G-protein coupled receptors, one of the largest families of membrane proteins.

Analysis of Agaricus meleagris pyranose dehydrogenase N-glycosylation sites and performance of partially non-glycosylated enzymes

Pyranose Dehydrogenase 1 from the basidiomycete Agaricus meleagris (AmPDH1) is an oxidoreductase capable of oxidizing a broad variety of sugars. Due to this and its ability of dioxidation of substrates and no side production of hydrogen peroxide, it is studied for use in enzymatic bio-fuel cells. In-vitro deglycosylated AmPDH1 as well as knock-out mutants of the N-glycosylation sites N⁷⁵ and N¹⁷⁵, near the active site entrance, were previously shown to improve achievable current densities of graphite electrodes modified with AmPDH1 and an osmium redox polymer acting as a redox mediator, up to 10-fold. For a better understanding of the role of N-glycosylation of AmPDH1, a systematic set of N-glycosylation site mutants was investigated in this work, regarding expression efficiency, enzyme activity and stability. Furthermore, the site specific extend of N-glycosylation was compared between native and recombinant wild type AmPDH1. Knocking out the site N²⁵² prevented the attachment of significantly extended N-glycan structures as detected on polyacrylamide gel electrophoresis, but did not significantly alter enzyme performance on modified electrodes. This suggests that not the molecule size but other factors like accessibility of the active site improved performance of deglycosylated AmPDH1/osmium redox polymer modified electrodes. A fourth N-glycosylation site of AmPDH1 could be confirmed by mass spectrometry at N³¹⁹, which appeared to be conserved in related fungal pyranose dehydrogenases but not in other members of the glucose-methanol-choline oxidoreductase structural family. This site was shown to be the only one that is essential for functional recombinant expression of the enzyme.

Cloning and expression of Saccharomyces cerevisiae SUC2 gene in yeast platform and characterization of recombinant enzyme biochemical properties

Invertase (EC.3.2.1.26) catalyzes the hydrolysis of sucrose to an equimolar mixture of D-glucose and D-fructose which is of interest for various industrial applications. In this research, Saccharomyces cerevisiae invertase gene (SUC2) was optimized based on Pichia pastoris codon preference. The synthetic gene was introduced into the methylotrophic yeast Pichia pastoris under the control of the inducible AOX1 promoter. High level of the extracellular recombinant invertase (R-inv) production was achieved via methanol induction for 4 days and purified by His-Tag affinity chromatography which appeared to be a mixture of glycosylated proteins with various sizes of 85-95 kDa on SDS-PAGE. Deglycosylation of the proteins by Endo-H resulted in the proteins with average molecular weight of 60 kDa. The purified recombinant invertase biochemical properties and kinetic parameters determined a pH and temperature optimum at 4.8 and 60 °C, respectively, which in comparison with native S. cerevisiae invertase, thermal stability of recombinant invertase is highly increased in different heating treatment experiments. The purification of recombinant invertase resulted in an enzyme with specific activity of 178.56 U/mg with 3.83-fold of purification and the kinetic constants for enzyme were Km value of 19 mM and Vmax value of 300 μmol min-1 mg-1 With kinetic efficiency (Kcat/Km) of 13.15 s-1 mmol-1 it can be concluded that recombinant P. pastoris invertase can be more effective for industrial quality criteria. We conclude that recombinant P. pastoris enzyme with broad pH stability, substrate specificity and proper thermal stability can fulfil a series of predefined industrial quality criteria to be used in food, pharmaceutical and bio ethanol production industries.

Tannase sequence from a xerophilic Aspergillus niger Strain and production of the enzyme in Pichia pastoris

Tannin acyl hydrolases, or tannases (EC 3.1.1.20), are enzymes with potential biotechnological applications. In this work, we describe the gene and amino acid sequences of the tannase from Aspergillus niger GH1. In addition, we engineered Pichia pastoris strains to produce and secrete the enzyme, and the produced tannase was characterized biochemically. The nucleotide sequence of mature tannase had a length of 1,686 bp, and encodes a protein of 562 amino acids. A molecular model of mature A. niger GH1 tannase showed the presence of two structural domains, one with an α/β-hydrolase fold and one lid domain that covers the catalytic site, likely being residues Ser-196, Asp-448, and His-494 the putative catalytic triad, which are connected by a disulfide bond between the neighboring cysteines, Cys-195 and Cys-495. A 120-ml shake flask culture with a constructed recombinant P. pastoris strain showed extracellular tannase activity at 48 h induction of 0.57 U/ml. The produced tannase was N-glycosylated, consisted of two subunits, likely linked by a disulfide bond, and had an optimum pH of 5.0 and optimum temperature of 20 °C. These biochemical properties differed from those of native A. niger GH1 tannase. The recombinant tannase could be suitable for food and beverage applications.

Recombinant horseradish peroxidase variants for targeted cancer treatment

Cancer is a major cause of death. Common chemo‐ and radiation‐therapies damage healthy tissue and cause painful side effects. The enzyme horseradish peroxidase (HRP) has been shown to activate the plant hormone indole‐3‐acetic acid (IAA) to a powerful anticancer agent in in vitro studies, but gene directed enzyme prodrug therapy (GDEPT) studies showed ambivalent results. Thus, HRP/IAA in antibody directed enzyme prodrug therapy (ADEPT) was investigated as an alternative. However, this approach has not been intensively studied, since the enzyme preparation from plant describes an undefined mixture of isoenzymes with a heterogenic glycosylation pattern incompatible with the human system. Here, we describe the recombinant production of the two HRP isoenzymes C1A and A2A in a Pichia pastoris benchmark strain and a glyco‐engineered strain with a knockout of the α‐1,6‐mannosyltransferase (OCH1) responsible for hypermannosylation. We biochemically characterized the enzyme variants, tested them with IAA and applied them on cancer cells. In the absence of H₂O₂, HRP C1A turned out to be highly active with IAA, independent of its surface glycosylation. Subsequent in vitro cytotoxicity studies with human T24 bladder carcinoma and MDA‐MB‐231 breast carcinoma cells underlined the applicability of recombinant HRP C1A with reduced surface glycoslyation for targeted cancer treatment. Summarizing, this is the first study describing the successful use of recombinantly produced HRP for targeted cancer treatment. Our findings might pave the way for an increased use of the powerful isoenzyme HRP C1A in cancer research in the future.

Protein Production with a Pichia pastoris OCH1 Knockout Strain in Fed-Batch Mode

The methylotrophic yeast Pichia pastoris is a widely used host organism for recombinant protein production in biotechnology and pharmaceutical industry. However, if the target product describes a glycoprotein, an α-1,6-mannosyltransferase located in the Golgi apparatus of P. pastoris, called OCH1, triggers hypermannosylation of the recombinant protein which significantly impedes following unit operations and hampers biopharmaceutical product applications. A knockout of the och1 gene allows the production of less-glycosylated proteins-however, morphology and physiology of P. pastoris also change, complicating the upstream process. Here, we describe a controlled and efficient bioprocess based on the specific substrate uptake rate (q s) for a recombinant P. pastoris OCH1 knockout strain expressing a peroxidase as model protein.

Integration and Validation of the Genome-Scale Metabolic Models of Pichia pastoris: A Comprehensive Update of Protein Glycosylation Pathways, Lipid and Energy Metabolism

Motivation

Genome-scale metabolic models (GEMs) are tools that allow predicting a phenotype from a genotype under certain environmental conditions. GEMs have been developed in the last ten years for a broad range of organisms, and are used for multiple purposes such as discovering new properties of metabolic networks, predicting new targets for metabolic engineering, as well as optimizing the cultivation conditions for biochemicals or recombinant protein production. Pichia pastoris is one of the most widely used organisms for heterologous protein expression. There are different GEMs for this methylotrophic yeast of which the most relevant and complete in the published literature are iPP668, PpaMBEL1254 and iLC915. However, these three models differ regarding certain pathways, terminology for metabolites and reactions and annotations. Moreover, GEMs for some species are typically built based on the reconstructed models of related model organisms. In these cases, some organism-specific pathways could be missing or misrepresented.

Results

In order to provide an updated and more comprehensive GEM for P. pastoris, we have reconstructed and validated a consensus model integrating and merging all three existing models. In this step a comprehensive review and integration of the metabolic pathways included in each one of these three versions was performed. In addition, the resulting iMT1026 model includes a new description of some metabolic processes. Particularly new information described in recently published literature is included, mainly related to fatty acid and sphingolipid metabolism, glycosylation and cell energetics. Finally the reconstructed model was tested and validated, by comparing the results of the simulations with available empirical physiological datasets results obtained from a wide range of experimental conditions, such as different carbon sources, distinct oxygen availability conditions, as well as producing of two different recombinant proteins. In these simulations, the iMT1026 model has shown a better performance than the previous existing models.

Carboxyl-terminal truncations alter the activity of the human α-galactosidase A

Fabry disease is an X-linked inborn error of glycolipid metabolism caused by deficiency of the human lysosomal enzyme, α-galactosidase A (αGal), leading to strokes, myocardial infarctions, and terminal renal failure, often leading to death in the fourth or fifth decade of life. The enzyme is responsible for the hydrolysis of terminal α-galactoside linkages in various glycolipids. Enzyme replacement therapy (ERT) has been approved for the treatment of Fabry disease, but adverse reactions, including immune reactions, make it desirable to generate improved methods for ERT. One approach to circumvent these adverse reactions is the development of derivatives of the enzyme with more activity per mg. It was previously reported that carboxyl-terminal deletions of 2 to 10 amino acids led to increased activity of about 2 to 6-fold. However, this data was qualitative or semi-quantitative and relied on comparison of the amounts of mRNA present in Northern blots with αGal enzyme activity using a transient expression system in COS-1 cells. Here we follow up on this report by constructing and purifying mutant enzymes with deletions of 2, 4, 6, 8, and 10 C-terminal amino acids (Δ2, Δ4, Δ6, Δ8, Δ10) for unambiguous quantitative enzyme assays. The results reported here show that the k_cat/K_m approximately doubles with deletions of 2, 4, 6 and 10 amino acids (0.8 to 1.7-fold effect) while a deletion of 8 amino acids decreases the k_cat/K_m (7.2-fold effect). These results indicate that the mutated enzymes with increased activity constructed here would be expected to have a greater therapeutic effect on a per mg basis, and could therefore reduce the likelihood of adverse infusion related reactions in Fabry patients receiving ERT treatment. These results also illustrate the principle that in vitro mutagenesis can be used to generate αGal derivatives with improved enzyme activity.

Development of a fed-batch process for a recombinant Pichia pastoris Δoch1 strain expressing a plant peroxidase

Pichia pastoris is a prominent host for recombinant protein production, amongst other things due to its capability of glycosylation. However, N-linked glycans on recombinant proteins get hypermannosylated, causing problems in subsequent unit operations and medical applications. Hypermannosylation is triggered by an α-1,6-mannosyltransferase called OCH1. In a recent study, we knocked out OCH1 in a recombinant P. pastoris CBS7435 Mut^S strain (Δoch1) expressing the biopharmaceutically relevant enzyme horseradish peroxidase. We characterized the strain in the controlled environment of a bioreactor in dynamic batch cultivations and identified the strain to be physiologically impaired. We faced cell cluster formation, cell lysis and uncontrollable foam formation.

In the present study, we investigated the effects of the 3 process parameters temperature, pH and dissolved oxygen concentration on 1) cell physiology, 2) cell morphology, 3) cell lysis, 4) productivity and 5) product purity of the recombinant Δoch1 strain in a multivariate manner. Cultivation at 30°C resulted in low specific methanol uptake during adaptation and the risk of methanol accumulation during cultivation. Cell cluster formation was a function of the C-source rather than process parameters and went along with cell lysis. In terms of productivity and product purity a temperature of 20°C was highly beneficial. In summary, we determined cultivation conditions for a recombinant P. pastoris Δoch1 strain allowing high productivity and product purity.

N-glycosylation site occupancy in human prostaglandin H synthases expressed in Pichia pastoris

Prostaglandin H synthases (PGHSs) are N-glycosylated membrane proteins that catalyse the committed step in prostaglandin synthesis. Unlike PGHS-2, the production of recombinant PGHS-1 in non-mammalian expression systems is complicated. The majority of the heterologous enzyme is inactive due to misfolding. Correct N-glycosylation is proposed to be obligatory for proper folding of mammalian PGHSs. In this study, human PGHS-1 and -2 (hPGHS-1 and -2) were expressed in the yeast Pichia pastoris. Recombinant hPGHS-2 was catalytically active, whereas hPGHS-1 was inactive. Accumulation of non-glycosylated hPGHSs was not observed in the crude lysate of the yeast cells. The N-glycosylation patterns of the purified recombinant proteins were characterised using nano-LC/MS/MS. The isoforms exhibited similar N-glycosylation site occupancy. The results indicate that there are more complex grounds for the inactivity of the recombinant hPGHS-1 produced in yeast.

Glycosylation analysis of recombinant neutral protease I from Aspergillus oryzae expressed in Pichia pastoris

Neutral protease I from Aspergillus oryzae 3.042 was expressed in Pichia pastoris and its N-glycosylation properties were analyzed. After purification by nickel-affinity chromatography column, the recombinant neutral protease (rNPI) was confirmed to be N-glycosylated by periodicacid/Schiff's base staining and Endo H digestion. Moreover, the deglycosylated protein's molecular weight decreased to 43.3 kDa from 54.5 kDa analyzed by SDS-PAGE and MALDI-TOF-MS, and the hyperglycosylation extent was 21 %. The N-glycosylation site of rNPI was analyzed by nano LC-MS/MS after digesting by trypsin and Glu-C, and the unique potential site Asn41 of mature peptide was found to be glycosylated. Homology modeling of the 3D structure of rNPI indicated that the attached N-glycans hardly affected neutral protease's activity due to the great distance away from the active site of the enzyme.

Mannosylated LigANI produced in Pichia pastoris protects hamsters against leptospirosis

The C-terminal region of the Leptospiral immunoglobulin-like A protein (LigA) contains six carboxy-terminal Ig-like repeat domains (LigANI). Subunit vaccine preparations based on recombinant LigANI produced in Escherichia coli, are promising vaccine candidates, albeit with variable efficacy. In the present study, LigANI was expressed in the methylotrophic yeast Pichia pastoris using a 12 L bioreactor to produce mannosylated LigANI (mLigANI) for use in a vaccine preparation against leptospirosis. Hamsters immunized with a mLigANI vaccine preparation produced a significant IgG antibody response (P < 0.001) and were protected (83.3 %; P < 0.001) against lethal challenge with 36× LD50 of a virulent strain of L. interrogans serovar Copenhageni. A vaccine preparation based on demannosylated mLigANI (nmLigANI) elicited an immune response in hamsters, but did not afford protection. The production of mLigANI in bioreactor by P. pastoris yielded ~50 mg L(-1) of recombinant protein. P. pastoris is a potential platform for the production of leptospiral antigens on an industrial scale. The results demonstrate that LigANI secreted by P. pastoris on mannosylated form (mLigANI) protect hamsters as subunit vaccine of L. interrogans lethal infection.

Engineering aggregation resistance in IgG by two independent mechanisms: lessons from comparison of Pichia pastoris and mammalian cell expression

Aggregation is an important concern for therapeutic antibodies, since it can lead to reduced bioactivity and increase the risk of immunogenicity. In our analysis of immunoglobulin G (IgG) molecules of identical amino acid sequence but produced either in mammalian cells (HEK293) or in the yeast Pichia pastoris (PP), dramatic differences in their aggregation susceptibilities were encountered. The antibodies produced in Pichia were much more resistant to aggregation under many conditions, a phenomenon found to be mainly caused by two factors. First, the mannose-rich glycan of the IgG from Pichia, while slightly thermally destabilizing the IgG, strongly inhibited its aggregation susceptibility, compared to the complex mammalian glycan. Second, on the Pichia-produced IgGs, amino acids belonging to the α-factor pre-pro sequence were left at the N-termini of both chains. These additional residues proved to considerably increase the temperature of the onset of aggregation and reduced the aggregate formation after extended incubation at elevated temperatures. The attachment of these residues to IgGs produced in cell culture confirmed their beneficial effect on the aggregation resistance. Secretion of IgGs with native N-termini in the yeast system became possible after systematic engineering of the precursor proteins and the processing site. Taken together, the present results will be useful for the successful production of full-length IgGs in Pichia, give indications on how to engineer aggregation-resistant IgGs and shed new light on potential biophysical effects of tag sequences in general.

Pichia pastoris-produced mucin-type fusion proteins with multivalent O-glycan substitution as targeting molecules for mannose-specific receptors of the immune system

Mannose-binding proteins like the macrophage mannose receptor (MR), the dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) and mannose-binding lectin (MBL) play crucial roles in both innate and adaptive immune responses. Immunoglobulin fusion proteins of the P-selectin glycoprotein ligand-1 (PSGL-1/mIgG(2b)) carrying mostly O-glycans and, as a control, the α1-acid glycoprotein (AGP/mIgG(2b)) carrying mainly N-linked glycans were stably expressed in the yeast Pichia pastoris. Pichia pastoris-produced PSGL-1/mIgG(2b) was shown to carry O-glycans that mediated strong binding to mannose-specific lectins in a lectin array and were susceptible to cleavage by α-mannosidases including an α1,2- but not an α1,6-mannosidase. Electrospray ionization ion-trap mass spectrometry confirmed the presence of O-glycans containing up to nine hexoses with the penta- and hexasaccharides being the predominant ones. α1,2- and α1,3-linked, but not α1,6-linked, mannose residues were detected by (1)H-nuclear magnetic resonance spectroscopy confirming the results of the mannosidase cleavage. The apparent equilibrium dissociation constants for binding of PNGase F-treated mannosylated PSGL-1/mIgG(2b) to MR, DC-SIGN and MBL were shown by surface plasmon resonance to be 126, 56 and 16 nM, respectively. In conclusion, PSGL-1/mIgG(2b) expressed in P. pastoris carried O-glycans mainly comprised of α-linked mannoses and with up to nine residues. It bound mannose-specific receptors with high apparent affinity and may become a potent targeting molecule for these receptors in vivo.

High yield expression of leptospirosis vaccine candidates LigA and LipL32 in the methylotrophic yeast Pichia pastoris

Background

Leptospirosis, a zoonosis caused by Leptospira spp., is recognized as an emergent infectious disease. Due to the lack of adequate diagnostic tools, vaccines are an attractive intervention strategy. Recombinant proteins produced in Escherichia coli have demonstrated promising results, albeit with variable efficacy. Pichia pastoris is an alternative host with several advantages for the production of recombinant proteins.

Results

The vaccine candidates LigANI and LipL32 were cloned and expressed in P. pastoris as secreted proteins. Large-scale expression resulted in a yield of 276 mg/L for LigANI and 285 mg/L for LipL32. The recombinant proteins were glycosylated and were recognized by antibodies present in the sera of patients with severe leptospirosis.

Conclusions

The expression of LigANI and LipL32 in P. pastoris resulted in a significant increase in yield compared to expression in E. coli. In addition, the proteins were secreted, allowing for easy purification, and retained the antigenic characteristics of the native proteins, demonstrating their potential application as subunit vaccine candidates.

High-level recombinant protein production in CHO cells using lentiviral vectors and the cumate gene-switch

Fast and efficient production of recombinant proteins for structural and functional studies is a crucial issue for research and for industry. To this end, we have developed an efficient system to generate in less than 2 months, starting from the cDNA, pools of CHO cells stably expressing high-level of recombinant proteins. It is based on lentiviral vectors (LVs) for stable transduction coupled with the cumate gene-switch for inducible and efficient gene expression. Transcription is initiated upon binding of the cumate transactivator (cTA) or the reverse cTA (rcTA) to the CR5 promoter. Binding of cTA or rcTA is prevented or induced by addition of cumate respectively. We first validated the CHO/LV production system with an LV carrying the secreted alkaline phosphatase (SEAP), whose expression was linked to the green fluorescent protein (GFP) through an internal ribosome entry site (IRES). CHO cells stably expressing the cTA (CHO-cTA) were transduced at various multiplicity of infection (MOI). Pools of cells were incubated at 37 and 30 degrees C during 10 days. Optimal SEAP production (65 microg/mL) was achieved at 30 degrees C with a MOI of 200. The pool stability was demonstrated for 48 days of culture by GFP expression analysis. The system was also evaluated using LV expressing three typical therapeutic proteins (a protein made up of the extracellular domain of CD200 fused to IgG Fc region [CD200Fc], a chimeric antibody [chB43], and erythropoietin [EPO]). CHO cells expressing rcTA (CHO-Cum2) were transduced with these LVs at a MOI of 200 and production was tested at 30 degrees C. After 13 days of culture, 235, 160, and 206 microg/mL of CD200Fc, chB43, and EPO were produced, respectively. The ON/OFF ratio of these pools was equal to 6 for CD200Fc, 16 for chB43, and 74 for EPO. In conclusion, this system should be very useful to produce mg quantities of recombinant proteins in a timely manner in serum free suspension culture of CHO cells for preclinical studies.

Expression of a Bacillus phytase C gene in Pichia pastoris and properties of the recombinant enzyme

The cloning and expression of a native gene encoding a Bacillus subtilis phytase using Pichia pastoris as the host is described. In addition, the influence of N-glycosylation on the biochemical properties of the B. subtilis phytase, the influence of pH on the thermostability of the recombinant and native B. subtilis phytases, and the resistance of both phytases to shrimp digestive enzymes and porcine trypsin are also described. After 48 h of methanol induction in shake flasks, a selected recombinant strain produced and secreted 0.82 U/ml (71 mg/liter) recombinant phytase. This phytase was N-glycosylated, had a molecular mass of 39 kDa after N-deglycosylation, exhibited activity within a pH range of 2.5 to 9 and at temperatures of 25 to 70 degrees C, had high residual activity (85% +/- 2%) after 10 min of heat treatment at 80 degrees C and pH 5.5 in the presence of 5 mM CaCl(2), and was resistant to shrimp digestive enzymes and porcine trypsin. Although the recombinant Bacillus phytase had pH and temperature activity profiles that were similar to those of the corresponding nonglycosylated native phytase, the thermal stabilities of the recombinant and native phytases were different, although both were calcium concentration and pH dependent.

Cloning and expression of a truncated form of envelope glycoprotein D of Bovine herpesvirus type 5 in methylotrophic yeast Pichia pastoris

Meningoencephalitis caused by Bovine herpesvirus type 5 (BoHV-5) is responsible for heavy economic losses in the cattle industry. As in other Alphaherpesviruses, the envelope glycoprotein IV (gD), which mediates penetration into host cells, is one of the major candidate antigens for a recombinant vaccine, since it induces a strong and persistent immune response. The DNA coding for a truncated form of BoHV-5 gD (tgD) has been cloned into the Pichia pastoris expression vector pPICZalphaB to allow protein secretion into the medium. After induction with methanol, a approximately 55kDa protein was obtained. Enzyme deglycosylation with Endo H showed a smaller size band in SDS-PGAE, with approximately 50kDa, suggesting that tgD has N-linked oligosaccharides and that it is not hyperglycosylated. The approximately 55kDa protein was recognized by several polyclonal antibodies, including polyclonal antibody anti-tgD and polyclonal antibodies of different animal species immunized with BoHV-5 and BoHV-1. This is the first report of BoHV-5 gD expression in yeast. It was shown that the recombinant truncated form of BoHV-5 gD has antigenic and immunogenic properties similar to the native BoHV-5 gD. Expression of tgD as a secreted protein allows simple and inexpensive purification methods that can be used for further studies to evaluate its immunogenicity in cattle.

Glycosylation and pH stability of penicillin G acylase from providencia rettgeri produced in Pichia pastoris

Penicillin G acylase (PAC) is one of the most widely used enzymes in industrial synthesis of semi-synthetic antibiotics. The Providencia rettgeri pac gene was expressed to a level of 2.7 U/ml using the Pichia pastoris expression system. The recombinant enzyme was purified and its glycosylation status was determined. It was found that both subunits (? and ?) of the enzyme were N-glycosylated, while the ?-subunit also contained O-glycans. It was also observed that rPACP.rett. was stable in a wide range of pH, which, in addition to the previously proved high thermostability, makes it an attractive biocatalyst from an industrial point of view.

Choice of cellular protein expression system

Recombinant protein expression has become a standard laboratory tool, and a wide variety of systems and techniques are now in use. Because there are so many systems to choose from, the investigator has to be careful to use the combination that will give the best results for the protein being studied. This overview unit discusses expression and production choices, including post-translational modifications (e.g., glycosylation, acylation, sulfation, and removal of N-terminal methionine), in vivo and in vitro folding, and influence of downstream elements on expression.

Influence of specific growth rate on specific productivity and glycosylation of a recombinant avidin produced by aPichia pastoris Mut+ strain

A recombinant avidin-producing Mut+ Pichia pastoris strain was used as a model organism to study the influence of the methanol feeding strategy on the specific product productivity (q(p)) and protein glycosylation. Fed-batch cultivations performed at various specific growth rates (micro) and residual methanol concentrations showed that the specific avidin productivity is growth-dependent. The specific productivity increases strongly with the specific growth rate for micro ranging from 0 to 0.02 h(-1), and increases only slightly with the specific growth rate above this limit. N-terminal glycosylation was also found to be influenced by the specific growth rate, since 9-mannose glycans were the most abundant form at low growth rates, whereas 10-mannose carbohydrate chains were favored at higher micro. These results show that culture parameters, such as the specific growth rate, may significantly affect the activity of glycoproteins produced in Pichia pastoris. In terms of process optimization, this suggests that a compromise on the specific growth rate may have to be found, in certain cases, to work with an acceptable productivity while avoiding the addition of many mannoses.

Vectors and strains for expression

Selection of both an appropriate expression vector and corresponding strain is crucial for successful expression of heterologous proteins in Pichia pastoris. This chapter explores both the standard and new vector/strain options available for protein expression in this yeast. Incorporated into expression vectors are selectable markers based on biosynthetic pathway genes, dominant drug resistance, or the P. pastoris formaldehyde dehydrogenase gene (FLD1). Novel strains available for expression include those that increase secretion of heterologous protein by overexpressing eukaryotic protein disulfide isomerase, and those that decrease hyperglycosylation or provide human-type glycosylation. This chapter also discusses methods to create multicopy strains that will potentially provide optimized expression of recombinant proteins in P. pastoris.

Approaches to achieve high-level heterologous protein production in plants

Plants offer an alternative to microbial fermentation and animal cell cultures for the production of recombinant proteins. For protein pharmaceuticals, plant systems are inherently safer than native and even recombinant animal sources. In addition, post-translational modifications, such as glycosylation, which cannot be achieved with bacterial fermentation, can be accomplished using plants. The main advantage foreseen for plant systems is reduced production costs. Plants should have a particular advantage for proteins produced in bulk, such as industrial enzymes, for which product pricing is low. In addition, edible plant tissues are well suited to the expression of vaccine antigens and pharmaceuticals for oral delivery. Three approaches have been followed to express recombinant proteins in plants: expression from the plant nuclear genome; expression from the plastid genome; and expression from plant tissues carrying recombinant plant viral sequences. The most important factor in moving plant-produced heterologous proteins from developmental research to commercial products is to ensure competitive production costs, and the best way to achieve this is to boost expression. Thus, considerable research effort has been made to increase the amount of recombinant protein produced in plants. This research includes molecular technologies to increase replication, to boost transcription, to direct transcription in tissues suited for protein accumulation, to stabilize transcripts, to optimize translation, to target proteins to subcellular locations optimal for their accumulation, and to engineer proteins to stabilize them. Other methods include plant breeding to increase transgene copy number and to utilize germplasm suited to protein accumulation. Large-scale commercialization of plant-produced recombinant proteins will require a combination of these technologies.

The role of mannosylated enzyme and the mannose receptor in enzyme replacement therapy

Lysosomal acid lipase (LAL) is the critical enzyme for the hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) in lysosomes. LAL defects cause Wolman disease (WD) and CE storage disease (CESD). An LAL null (lal-/-) mouse model closely mimics human WD/CESD, with hepatocellular, Kupffer cell and other macrophage, and adrenal cortical storage of CEs and TGs. The effect on the cellular targeting of high-mannose and complex oligosaccharide-type oligosaccharide chains was tested with human LAL expressed in Pichia pastoris (phLAL) and CHO cells (chLAL), respectively. Only chLAL was internalized by cultured fibroblasts, whereas both chLAL and phLAL were taken up by macrophage mannose receptor (MMR)-positive J774E cells. After intraperitoneal injection into lal-/- mice, phLAL and chLAL distributed to macrophages and macrophage-derived cells of various organs. chLAL was also detected in hepatocytes. Ten injections of either enzyme over 30 d into 2- and 2.5-mo-old lal-/- mice produced normalization of hepatic color, decreased liver weight (50%-58%), and diminished hepatic cholesterol and TG storage. Lipid accumulations in macrophages were diminished with either enzyme. Only chLAL cleared lipids in hepatocytes. Mice double homozygous for the LAL and MMR deficiences (lal-/-;MMR-/-) showed phLAL uptake into Kupffer cells and hepatocytes, reversal of macrophage histopathology and lipid storage in all tissues, and clearance of hepatocytes. These results implicate MMR-independent and mannose 6-phosphate receptor-independent pathways in phLAL uptake and delivery to lysosomes in vivo. In addition, these studies show specific cellular targeting and physiologic effects of differentially oligosaccharide-modified human LALs mediated by MMR and that lysosomal targeting of mannose-terminated glycoproteins occurs and storage can be eliminated effectively without MMR.

De-glycosylation of Pichia pastoris-produced Schistosoma mansoni cathepsin B eliminates non-specific reactivity with IgG in normal human serum

Production of diagnostic reagents in the yeast Pichia pastoris is particularly attractive since this organism is capable of expressing complex eukaryotic proteins in their correctly folded form and is amenable to large-scale fermentation at low cost. The potential of Schistosoma mansoni cathepsin B as a diagnostic antigen for human schistosomiasis has been previously established using both native and E. coli-derived recombinant proteins. However, when produced in P. pastoris we found that recombinant wild-type cathepsin B was preferentially secreted as a heterogeneously glycosylated molecule that migrated at 39 kDa, 41 kDa and a smear of >50 kDa on SDS-PAGE, and was susceptible to treatment with Endo H and PGNase F. The addition of yeast sugars to the cathepsin B caused it to react with IgG in the serum of both normal (non-infected) and schistosome-infected humans in immunoblotting and enzyme linked immunosorbent assays (ELISA). To avoid this non-specific reactivity, a non-glycosylated mutant form of cathepsin B, engineered by disrupting its potential glycosylation site, was produced. The non-glycosylated recombinant cathepsin B migrated as a single band of 39 kDa on SDS-PAGE. Most importantly, the molecule was not reactive with IgG in normal sera and, hence, could be employed in immunoblots or ELISA to specifically detect antibodies in schistosome-infected patients. Addition of oligosaccharides by P. pastoris is a potential drawback that needs to be considered before using P. pastoris-produced proteins as diagnostic reagents.

High-level expression and immunogenic properties of the recombinant rabbit hemorrhagic disease virus VP60 capsid protein obtained in Pichia pastoris

The VP60 capsid protein from rabbit hemorrhagic disease virus (RHDV) (Spanish isolate AST/89) was cloned and expressed in Pichia pastoris. The transformed yeast was grown at high cell density and an expression level of about 1.5 g VP60L(-1) culture was obtained. The protein was detected associated with the cell debris fraction of the recombinant yeast after mechanical disruption. It was purified by a simple method and was obtained N-glycosylated with purity of approximately 70% as deduced from densitometry scan analysis. The recombinant product was antigenically similar to the native capsid protein as determined with polyclonal antibodies obtained from rabbits vaccinated with VP60 protein purified from native virus. The immunogenicity of VP60 protein purified from P. pastoris was demonstrated by ELISA in a vaccination experiment conducted with two groups of rabbits subcutaneously immunized. Animals vaccinated with VP60 in Freund's incomplete adjuvant developed a significant (p<0.01) virus-specific antibody response while the group injected with placebo remained seronegative. Preliminary results showed that the antigen administered within the cell debris fraction of the transformed yeast protected rabbits immunized by the oral route against an intramuscular challenge with 100 LD50 (16,000 hemagglutination units) of homologous virus.

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.

Heterologous protein production using thePichia pastoris expression system

The Pichia pastoris expression system is being used successfully for the production of various recombinant heterologous proteins. Recent developments with respect to the Pichia expression system have had an impact on not only the expression levels that can be achieved, but also the bioactivity of various heterologous proteins. We review here some of these recent developments, as well as strategies for reducing proteolytic degradation of the expressed recombinant protein at cultivation, cellular and protein levels. The problems associated with post-translational modifications performed on recombinant proteins by P. pastoris are discussed, including the effects on bioactivity and function of these proteins, and some engineering strategies for minimizing unwanted glycosylations. We pay particular attention to the importance of optimizing the physicochemical environment for efficient and maximal recombinant protein production in bioreactors and the role of process control in optimizing protein production is reviewed. Finally, future aspects of the use of the P. pastoris expression system are discussed with regard to the production of complex membrane proteins, such as G protein-coupled receptors, and the industrial and clinical importance of these proteins.

The effect of nitrogen source on yield and glycosylation of a human cystatin C mutant expressed in Pichia pastoris

Human cystatin C is a cysteine proteinase inhibitor with potential applications as an anti-viral agent, cancer tumor growth inhibitor, and in prevention of proteolysis during food processing. A glycosylated cystatin C mutant with increased temperature stability was developed for the latter application [Nakamura et al. (1998) FEBS Lett 427:252-254]. A recombinant variant of cystatin C [Nakamura et al. (2000) International patent no. PLTCA99/00717] with two potential sites for N-linked glycosylation was expressed in Pichia pastoris Mut(s). Little of the cystatin C produced was in the glycosylated form under fermentation conditions of pH 6, temperature 28 degrees C, methanol only feed, and ammonium hydroxide as a nitrogen source. Thus, the effect of addition of complex nitrogen sources, peptone and amino acid supplements, on the yield and glycosylation of this mutant cystatin C were investigated. A full factorial design experiment using 2-l fermenters was performed with three factors: ammonium hydroxide, peptone, and an amino acid mix, at two levels, absent or present. Peptone addition was found to have a positive, and the most significant, effect on cell specific cystatin C yield. A maximum mutant cystatin C yield of 0.82 mumol (g-dry cell weight)(-1) min(-1) was obtained when all three nitrogen sources were used together. However, under these conditions only 16% of protein was in the glycosylated form since ammonia was found to have a significant negative effect on glycosylation extent. The maximum extent of glycosylation was 30% when peptone and amino acid mix were the only nitrogen sources added.

Expression and characterization of the first kunitz domain of human tissue factor pathway inhibitor-2

Human tissue factor pathway inhibitor-2 (hTFPI-2) has three kunitz domains whose structure and function are unclear. We expressed the first kunitz domain of hTFPI-2 (hTFPI-2/KD1) as functional form using Pichia pastoris and investigated its characterization. In the experiment, hTFPI-2/KD1 can inhibit the plasmin and trypsin activity and the Ki of hTFPI-2/KD1 towards plasmin (30nM) and trypsin (50nM) was determined as 10 and 7nM by chromogenic assay, respectively. hTFPI-2/KD1 can also inhibit MMP-2 and MMP-9 in zymography assay. Furthermore, the inhibition of hTFPI-2/KD1 to the Matrigel invasion by HT-1080 is also described. This study provides a method to produce hTFPI-2/KD1 efficiently and some insights into the structure and function of hTFPI-2/KD1.

Cloning and disruption of the PpURA5 gene and construction of a set of integration vectors for the stable genetic modification of Pichia pastoris

A pair of degenerate primers was used for amplification and cloning of a DNA fragment containing parts of the P. pastoris URA5 and SEC65 genes. Using additional information from a partial genomic sequence of P. pastoris, we cloned and sequenced a 1.9 kb chromosomal fragment containing the complete orotate-phosphoribosyltransferase-encoding URA5 gene. A disruption cassette was constructed by replacing a small part of the open reading frame with a kanamycin-resistance gene. The P. pastoris wild-type strain NRRL Y-11430 was transformed with the disruption cassette and an ura5 auxotrophic strain was identified. To generate marker constructs that can be reused in successive transformations of a single strain, we constructed two lacZ-PpURA3-lacZ and lacZ-PpURA5-lacZ cassettes and used them to disrupt PpOCH1. The PpURA3 and PpURA5 genes in the disruptants were then successfully recycled by selecting for resistance to 5'-fluoro-orotic acid. We also assembled a set of modular plasmids that can be used for the stable genetic modification of P. pastoris via a double cross-over event. The sequence presented here has been submitted to the EMBL data library under Accession No. AY303544.

Cloning and characterization in Pichia pastoris of PNO1 gene required for phosphomannosylation of N-linked oligosaccharides

The yeast Pichia pastoris PNO1 (Phosphomannosylation of N-linked Oligosaccharides) gene, which is involved in phosphomannosylation of N-linked oligosaccharides, was cloned using the Saccharomyces cerevisiae MNN4 gene [Glycobiology 6 (1996) 805] as a probe. The PNO1 open reading frame (ORF) encodes a type II membrane protein composed of 777 amino acid residues. Only in the short region extending from amino acid position 450 to 606 of Pno1p, sequence homology to S. cerevisiae Mnn4p was observed at a level of 45%. The tandem repeat sequence of Lys-Lys-Lys-Lys-Glu-Glu-Glu-Glu characteristic of the C-terminal region of S. cerevisiae Mnn4p is not present in Pno1p. To investigate the function of the PNO1 gene, we constructed a PNO1 gene disruptant by replacement with an expression cassette of human antithrombin (AT), a glycoprotein in plasma. The cell growth and recombinant human antithrombin (rAT) production levels of the disruptant were similar to those of recombinant human antithrombin-expressing wild-type strains. Moreover, the level of alcian blue dye cell staining, which shows the presence of acidic sugar chains on the cell surface, was also similar. However, the phosphomannosylation ratio of N-linked oligosaccharides on recombinant human antithrombin decreased dramatically from 20% in wild-type strains to less than 1% in the PNO1 disruptant. When the PNO1 gene was re-introduced into the disruptant, the phosphomannosylation ratio recovered to the original level. These results suggest that the newly cloned PNO1 gene promotes phosphomannosylation only to core-like oligosaccharides, and not to the hypermannosylated outer chain, and that it has a different function from the MNN4 gene, which promotes the phosphomannosylation of both core and outer sugar chains.

N-linked glycosylation of native and recombinant cauliflower xyloglucan endotransglycosylase 16A

The gene encoding a XET (xyloglucan endotransglycosylase) from cauliflower ( Brassica oleracea var. botrytis ) florets has been cloned and sequenced. Sequence analysis indicated a high degree of similarity to other XET enzymes belonging to glycosyl hydrolase family 16 (GH16). In addition to the conserved GH16 catalytic sequence motif EIDFE, there exists one potential N-linked glycosylation site, which is also highly conserved in XET enzymes from this family. Purification of the corresponding protein from extracts of cauliflower florets allowed the fractionation of a single, pure glycoform, which was analysed by MS techniques. Accurate protein mass determination following the enzymic deglycosylation of this glycoform indicated the presence of a high-mannose-type glycan of the general structure GlcNAc2Man6. LC/MS and MS/MS (tandem MS) analysis provided supporting evidence for this structure and confirmed that the glycosylation site (underlined) was situated close to the predicted catalytic residues in the conserved sequence YLSSTNNEHDEIDFEFLGNRTGQPVILQTNVFTGGK. Heterologous expression in Pichia pastoris produced a range of protein glycoforms, which were, on average, more highly mannosylated than the purified native enzyme. This difference in glycosylation did not influence the apparent enzymic activity of the enzyme significantly. However, the removal of high-mannose glycosylation in recombinant cauliflower XET by endoglycosidase H, quantified by electrospray-ionization MS, caused a 40% decrease in the transglycosylation activity of the enzyme. No hydrolytic activity was detected in native or heterologously expressed BobXET16A, even when almost completely deglycosylated.

Characterization of N-linked oligosaccharides attached to recombinant human antithrombin expressed in the yeast Pichia pastoris

We studied the structures of four N-linked oligosaccharide chains of the recombinant human antithrombin (rAT) expressed in the yeast Pichia pastoris. rAT was fully glycosylated at Asn 96 and Asn 155, whereas the glycosylation on Asn 135 and Asn 192 was partial. The glycosylation level on Asn 135 was only 12% and this reduction is assumed to be one of the reasons for a higher heparin-binding affinity of rAT than plasma-derived human antithrombin (pAT). In order to determine the sizes and electrostatic charges of the N-linked oligosaccharides, rAT was treated with PNGase F, and the reduced ends were labelled by pyridylamination followed by analysis using anion exchange and amide adsorption columns. The N-linked oligosaccharides were 78% neutral and 22% phosphomannosylated. The neutral oligosaccharides were thought to be Man(9-12)GlcNAc(2) as their major components. The phosphomannosylated oligosaccharides were then subjected to mild acid hydrolysis and/or digestion with alkaline phosphatase, and their charge shifts were analysed by the affinity to an anion exchange column. Among phosphomannosylated oligosaccharides, monophosphate diester type was predominant, whereas negatively charged diphosphate diester and monophosphate monoester types were minor components. The mannose residues at the non-reducing end(s) of Man(9-12)GlcNAc(2) were phosphomannosylated or phosphorylated and these are the major components. Because rAT is less negatively charged than pAT, which has disialyl biantennary N-glycans, it might be less repulsive to pentasaccharide-bearing anticoagulantly active heparan sulphate proteoglycan molecules exposed on the surface of the damaged vascular vessels.

Expression and characterization of sweet potato invertase in Pichia pastoris

An invertase cDNA (Ibbetafruct1) was cloned from sweet potato leaves and characterized. The deduced amino acid sequence of the Ibbetafruct1-encoded protein was closely related to vacuolar invertases and included the WECVD catalytic domain characteristic of them. An expression plasmid containing the coding region of Ibbetafruct1 under the control of the alcohol oxidase promoter was used to transform the methylotrophic yeast Pichia pastoris. The biochemical properties for the expressed recombinant enzyme, which was determined to be the acid beta-fructofuranosidase with an acidic pI value (5.1), were similar to those of vacuolar invertases purified from sweet potato. Periodic acid/Schiff staining and Con A-Sepharose gel-binding experiments revealed the recombinant invertase to be a glycoprotein containing glucose and/or mannose residues. Furthermore, the carbohydrate moiety appears to be a key determinant of the enzyme's sucrose hydrolysis activity, substrate affinity, and thermal stability.

A single mutation in the activation site of bovine trypsinogen enhances its accumulation in the fermentation broth of the yeast Pichia pastoris

We produced bovine trypsinogen in the yeast Pichia pastoris. Little or no trypsinogen was detected when the gene with its native leader sequence was expressed under the control of the strong aox1 promoter, suggesting that expression of the wild-type bovine trypsinogen was toxic to the cells. We altered the trypsinogen native propeptide sequence by replacing the lysine at position 6 with an aspartic acid, thus destroying the site in the propeptide cleaved by enterokinase and by trypsin. This mutant accumulated up to 10 mg of trypsinogen per liter in shake flask cultures and about 40 mg/liter in 6-liter fermentors. Trypsinogen could be activated in vitro with a dipeptidyl-aminopeptidase, which selectively removed the modified trypsinogen propeptide; the resulting trypsin was fully active and showed evidence of glycosylation. Thus, we have developed a novel protein production scheme that can be used for the expression of proteins, such as proteases, that are deleterious to the producing organism. This system relies on the expression of a zymogen that cannot be activated in vivo coupled with its in vitro purification and activation.

Expression and characterization of a synthetic protein C activator in Pichia pastoris

Protein C activators are proteases that activate protein C in the mammalian coagulation system. A reptilian protein C activator is a critical component in current functional assays for protein C, its cofactor protein S, as well as for the overall status of the protein C pathway. We have constructed a synthetic gene for a protein C activator, based on a published snake-venom polypeptide sequence. This recombinant protein C activator was expressed in Pichia pastoris as a secreted glycoprotein (ILPCA) using the AOX1 promoter and the alpha-factor signal sequence. A fermentation protocol was developed that produced about 150 mg/L biologically active ILPCA secreted in the fermented broth. A two-step purification scheme was devised to purify ILPCA to approximately 80% purity. The ILPCA produced has an apparent molecular weight of approximately 68 kDa and a deglycosilated molecular weight of 28 kDa. Steady-state kinetic analysis reveals that ILPCA activates purified human protein C with a K(m) of 77 nM and a k(cat) of 0.39 s(-1). In conclusion, ILPCA is a recombinant protein that can be produced reliably and in large quantities under controlled manufacturing conditions, activates protein C, and can be used in coagulation assays as an alternative to native venom preparations.

Large-scale production, purification, and characterisation of recombinant Phaseolus vulgaris phytohemagglutinin E-form expressed in the methylotrophic yeast Pichia pastoris

The kidney bean lectin Phaseolus vulgaris phytohemagglutinin E-form (PHA-E) was expressed and secreted by the methylotrophic yeast Pichia pastoris. To optimise yields of PHA-E, transformants of P. pastoris were selected for high-level production of the recombinant protein. A scaleable process for the production and purification of gram quantities of recombinant PHA-E is reported. PHA-E was secreted at approximately 100 mg/L at the 2- and 200-L scale and was purified to 95% homogeneity in a single step using cation-exchange chromatography. The purified recombinant PHA-E consists of four forms with molecular masses between 28.5 and 31.5 kDa, as assessed by MALDI-TOF, whereas its native counterpart has a molecular mass of approximately 30.5 kDa. Endoglycosidase treatment revealed that the range in size of the recombinant protein was attributed to differences in the nature of the N-linked oligosaccharides bound to the protein. The primary amino acid sequence of the recombinant PHA-E was found to be identical to the native protein and to have an agglutination activity similar to that of native PHA-E. The data presented here suggest that, using P. pastoris, gram quantities of a recombinant phytohemagglutinin E-form can be produced and that the recombinant protein is similar to the protein synthesised in plants with respect to structure and biological activity.