A combinatorial genetic library approach to target heterologous glycosylation enzymes to the endoplasmic reticulum or the Golgi apparatus of Pichia pastoris

Improved production of recombinant β-mannanase (TaMan5) in Pichia pastoris and its synergistic degradation of lignocellulosic biomass

Mannan, a highly abundant and cost-effective natural resource, holds great potential for the generation of high-value compounds such as bioactive polysaccharides and biofuels. In this study, we successfully enhanced the expression of constructed GH5 β-mannanase (TaMan5) from Trichoderma asperellum ND-1 by employing propeptide in Pichia pastoris. By replacing the α-factor with propeptide (MGNRALNSMKFFKSQALALLAATSAVA), TaMan5 activity was significantly increased from 67.5 to 91.7 U/mL. It retained higher activity in the presence of 20% ethanol and 15% NaCl. When incubated with a high concentration of mannotriose or mannotetraose, the transglycosylation action of TaMan5 can be detected, yielding the corresponding production of mannotetraose or mannooligosaccharides. Moreover, the unique mechanism whereby TaMan5 catalyzes the degradation of mannan into mannobiose involves the transglycosylation of mannose to mannotriose or mannotetraose as a substrate to produce a mannotetraose or mannopentose intermediate, respectively. Additionally, the production of soluble sugars from lignocellulose is a crucial step in bioethanol development, and it is noteworthy that TaMan5 could synergistically yield fermentable sugars from corn stover and bagasse. These findings offered valuable insights and strategies for enhancing β-mannanase expression and efficient conversion of lignocellulosic biomass, providing cost-effective and sustainable approaches for high-value biomolecule and biofuel production.

Synthetic Glycobiology: Parts, Systems, and Applications

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

A new pH sensor localized in the Golgi apparatus of Saccharomyces cerevisiae reveals unexpected roles of Vph1p and Stv1p isoforms

The gradual acidification of the secretory pathway is conserved and extremely important for eukaryotic cells, but until now there was no pH sensor available to monitor the pH of the early Golgi apparatus in Saccharomyces cerevisiae. Therefore, we developed a pHluorin-based sensor for in vivo measurements in the lumen of the Golgi. By using this new tool we show that the cis- and medial-Golgi pH is equal to 6.6–6.7 in wild type cells during exponential phase. As expected, V-ATPase inactivation results in a near neutral Golgi pH. We also uncover that surprisingly Vph1p isoform of the V-ATPase is prevalent to Stv1p for Golgi acidification. Additionally, we observe that during changes of the cytosolic pH, the Golgi pH is kept relatively stable, mainly thanks to the V-ATPase. Eventually, this new probe will allow to better understand the mechanisms involved in the acidification and the pH control within the secretory pathway.

Tailoring N-Glycan Biosynthesis for Production of Therapeutic Proteins in Saccharomyces cerevisiae

The ability to control and adjust the N-glycosylation pathway of Saccharomyces cerevisiae is a key step toward production of therapeutic glycoproteins such as antibodies or erythropoietin. The focus of this chapter is to describe the road from yeast-type N-glycosylation to human-type complex N-glycosylation. The chapter describes the cell engineering and provides the detailed analytical procedures required to perform glycan analysis using MALDI-TOF mass spectrometry.

Production of a recombinant peroxidase in different glyco-engineered Pichia pastoris strains: a morphological and physiological comparison

Background

The methylotrophic yeast Pichia pastoris is a common host for the production of recombinant proteins. However, hypermannosylation hinders the use of recombinant proteins from yeast in most biopharmaceutical applications. Glyco-engineered yeast strains produce more homogeneously glycosylated proteins, but can be physiologically impaired and show tendencies for cellular agglomeration, hence are hard to cultivate. Further, comprehensive data regarding growth, physiology and recombinant protein production in the controlled environment of a bioreactor are scarce.

Results

A Man₅GlcNAc₂ glycosylating and a Man_8–10GlcNAc₂ glycosylating strain showed similar morphological traits during methanol induced shake-flask cultivations to produce the recombinant model protein HRP C1A. Both glyco-engineered strains displayed larger single and budding cells than a wild type strain as well as strong cellular agglomeration. The cores of these agglomerates appeared to be less viable. Despite agglomeration, the Man₅GlcNAc₂ glycosylating strain showed superior growth, physiology and HRP C1A productivity compared to the Man_8–10GlcNAc₂ glycosylating strain in shake-flasks and in the bioreactor. Conducting dynamic methanol pulsing revealed that HRP C1A productivity of the Man₅GlcNAc₂ glycosylating strain is best at a temperature of 30 °C.

Conclusion

This study provides the first comprehensive evaluation of growth, physiology and recombinant protein production of a Man₅GlcNAc₂ glycosylating strain in the controlled environment of a bioreactor. Furthermore, it is evident that cellular agglomeration is likely triggered by a reduced glycan length of cell surface glycans, but does not necessarily lead to lower metabolic activity and recombinant protein production. Man₅GlcNAc₂ glycosylated HRP C1A production is feasible, yields active protein similar to the wild type strain, but thermal stability of HRP C1A is negatively affected by reduced glycosylation.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1032-6) contains supplementary material, which is available to authorized users.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Optimizing antibody expression: The nuts and bolts

Antibodies are extensively utilized entities in biomedical research, and in the development of diagnostics and therapeutics. Many of these applications require high amounts of antibodies. However, meeting this ever-increasing demand of antibodies in the global market is one of the outstanding challenges. The need to maintain a balance between demand and supply of antibodies has led the researchers to discover better means and methods for optimizing their expression. These strategies aim to increase the volumetric productivity of the antibodies along with the reduction of associated manufacturing costs. Recent years have witnessed major advances in recombinant protein technology, owing to the introduction of novel cloning strategies, gene manipulation techniques, and an array of cell and vector engineering techniques, together with the progress in fermentation technologies. These innovations were also highly beneficial for antibody expression. Antibody expression depends upon the complex interplay of multiple factors that may require fine tuning at diverse levels to achieve maximum yields. However, each antibody is unique and requires individual consideration and customization for optimizing the associated expression parameters. This review provides a comprehensive overview of several state-of-the-art approaches, such as host selection, strain engineering, codon optimization, gene optimization, vector modification and process optimization that are deemed suitable for enhancing antibody expression.

Characterization and high-yield production of non-N-glycosylated recombinant human BCMA-Fc in Pichia pastoris

B-cell maturation antigen (BCMA) fused at the C-terminus to the Fc portion of human IgG1 (BCMA-Fc) blocks B-cell activating factor (BAFF) and proliferation-inducing ligand (APRIL)-mediated B-cell activation, leading to immune disorders. The fusion protein has been cloned and produced by several engineering cell lines. To reduce cost and enhance production, we attempted to express recombinant human BCMA-Fc (rhBCMA-Fc) in Pichia pastoris under the control of the AOX1 methanol-inducible promoter. To produce the target protein with uniform molecular weight and reduced immunogenicity, we mutated two predicted N-linked glycosylation sites. The secretory yield was improved by codon optimization of the target gene sequence. After fed-batch fermentation under optimized conditions, the highest yield (207 mg/L) of rhBCMA-Fc was obtained with high productivity (3.45 mg/L/h). The purified functional rhBCMA-Fc possessed high-binding affinity to APRIL and dose-dependent inhibition of APRIL-induced proliferative activity in vitro through three-step purification. Thus, this yeast-derived expression method could be a low-cost and effective alternative to the production of rhBCMA-Fc in mammalian cell lines.

Manganese ion concentration affects production of human core 3 O-glycan in Saccharomyces cerevisiae

BACKGROUND

Production of various mucin-like glycoproteins could be useful for development of antibodies specific to disease-related glycoproteins as well as for the biosynthesis of clinically useful glycoproteins. A Saccharomyces cerevisiae strain capable of in vivo production of mucin-type core 1 structure (Galβ1-3GalNAcα1-O-Ser/Thr) has been reported, but a strain producing core 3 structure (GlcNAcβ1-3GalNAcα1-O-Ser/Thr) has not been constructed.

METHODS

To generate core 3-producing strain, genes encoding uridine diphosphate (UDP)-Gal-4-epimerase, UDP-GalNAc transporter, UDP-GlcNAc transporter, and two glycosyltransferases were integrated into the genome. A Mucin-1-derived acceptor peptide (MUC1ap) was expressed as an acceptor. The amount of the resulting modified peptide was analyzed by HPLC.

RESULTS

Introduction of a codon-optimized UDP-GlcNAc:βGal β-1,3-N-acetylglucosaminyltransferase 6 (β3Gn-T6) gene yielded increases in β3Gn-T6 activity but did not alter the level of core 3 production. The highest in vitro activity of β3Gn-T6 was observed at Mn(2+) concentrations of 10mM and above. Supplementation of MnCl2 to the culture medium yielded increases of up to 25% in the accumulation of core 3 on the MUC1ap. The yeast invertase from the core 3-producing strain was less extensively N-glycosylated; however, it was partially restored by the addition of MnCl2 to the medium.

CONCLUSIONS

Physiological Mn(2+) concentration in S. cerevisiae was insufficient to facilitate optimal synthesis of core 3. Mn(2+) supplementation led to up-regulation of reaction of glycosylation in the Golgi, resulting in increases of core 3 production.

GENERAL SIGNIFICANCE

This study reveals that control of Mn(2+) concentration is important for production of specific mammalian-type glycans in S. cerevisiae.

Glycosylation of Cellulases: Engineering Better Enzymes for Biofuels

Cellulose in plant cell walls is the largest reservoir of renewable carbon on Earth. The saccharification of cellulose from plant biomass into soluble sugars can be achieved using fungal and bacterial cellulolytic enzymes, cellulases, and further converted into fuels and chemicals. Most fungal cellulases are both N- and O-glycosylated in their native form, yet the consequences of glycosylation on activity and structure are not fully understood. Studying protein glycosylation is challenging as glycans are extremely heterogeneous, stereochemically complex, and glycosylation is not under direct genetic control. Despite these limitations, many studies have begun to unveil the role of cellulase glycosylation, especially in the industrially relevant cellobiohydrolase from Trichoderma reesei, Cel7A. Glycosylation confers many beneficial properties to cellulases including enhanced activity, thermal and proteolytic stability, and structural stabilization. However, glycosylation must be controlled carefully as such positive effects can be dampened or reversed. Encouragingly, methods for the manipulation of glycan structures have been recently reported that employ genetic tuning of glycan-active enzymes expressed from homogeneous and heterologous fungal hosts. Taken together, these studies have enabled new strategies for the exploitation of protein glycosylation for the production of enhanced cellulases for biofuel production.

Progress in Yeast Glycosylation Engineering

While yeast are lower eukaryotic organisms, they share many common features and biological processes with higher eukaryotes. As such, yeasts have been used as model organisms to facilitate our understanding of such features and processes. To this end, a large number of powerful genetic tools have been developed to investigate and manipulate these organisms. Going hand-in-hand with these genetic tools is the ability to efficiently scale up the fermentation of these organisms, thus making them attractive hosts for the production of recombinant proteins. A key feature of producing recombinant proteins in yeast is that these proteins can be readily secreted into the culture supernatant, simplifying any downstream processing. A consequence of this secretion is that the proteins typically pass through the secretory pathway, during which they may be exposed to various posttranslational modifications. The addition of glycans is one such modification. Unfortunately, while certain aspects of glycosylation are shared between lower and higher eukaryotes, significant differences exist. Over the last two decades much research has focused on engineering the glycosylation pathways of yeast to more closely resemble those of higher eukaryotes, particularly those of humans for the production of therapeutic proteins. In the current review we shall highlight some of the key achievements in yeast glyco-engineering which have led to humanization of both the N- and O-linked glycosylation pathways.

Biopharmaceutical discovery and production in yeast

The selection of an expression platform for recombinant biopharmaceuticals is often centered upon suitable product titers and critical quality attributes, including post-translational modifications. Although notable differences between microbial, yeast, plant, and mammalian host systems exist, recent advances have greatly mitigated any inherent liabilities of yeasts. Yeast expression platforms are important to both the supply of marketed biopharmaceuticals and the pipelines of novel therapeutics. In this review, recent advances in yeast-based expression of biopharmaceuticals will be discussed. The advantages of using glycoengineered yeast as a production host and in the discovery space will be illustrated. These advancements, in turn, are transforming yeast platforms from simple production systems to key technological assets in the discovery and selection of biopharmaceutical lead candidates.

Protein expression in Pichia pastoris: recent achievements and perspectives for heterologous protein production

Pichia pastoris is an established protein expression host mainly applied for the production of biopharmaceuticals and industrial enzymes. This methylotrophic yeast is a distinguished production system for its growth to very high cell densities, for the available strong and tightly regulated promoters, and for the options to produce gram amounts of recombinant protein per litre of culture both intracellularly and in secretory fashion. However, not every protein of interest is produced in or secreted by P. pastoris to such high titres. Frequently, protein yields are clearly lower, particularly if complex proteins are expressed that are hetero-oligomers, membrane-attached or prone to proteolytic degradation. The last few years have been particularly fruitful because of numerous activities in improving the expression of such complex proteins with a focus on either protein engineering or on engineering the protein expression host P. pastoris. This review refers to established tools in protein expression in P. pastoris and highlights novel developments in the areas of expression vector design, host strain engineering and screening for high-level expression strains. Breakthroughs in membrane protein expression are discussed alongside numerous commercial applications of P. pastoris derived proteins.

New opportunities by synthetic biology for biopharmaceutical production in Pichia pastoris

Biopharmaceuticals are an integral part of modern medicine and pharmacy. Both, the development and the biotechnological production of biopharmaceuticals are highly cost-intensive and require suitable expression systems. In this review we discuss established and emerging tools for reengineering the methylotrophic yeast Pichia pastoris for biopharmaceutical production. Recent advancements of this industrial expression system through synthetic biology include synthetic promoters to avoid methanol induction and to fine-tune protein production. New platform strains and molecular cloning tools as well as in vivo glycoengineering to produce humanized glycoforms have made P. pastoris an important host for biopharmaceutical production.

Knockout of an endogenous mannosyltransferase increases the homogeneity of glycoproteins produced in Pichia pastoris

The yeast Pichia pastoris is a common host for the recombinant production of biopharmaceuticals, capable of performing posttranslational modifications like glycosylation of secreted proteins. However, the activity of the OCH1 encoded α-1,6-mannosyltransferase triggers hypermannosylation of secreted proteins at great heterogeneity, considerably hampering downstream processing and reproducibility. Horseradish peroxidases are versatile enzymes with applications in diagnostics, bioremediation and cancer treatment. Despite the importance of these enzymes, they are still isolated from plant at low yields with different biochemical properties. Here we show the production of homogeneous glycoprotein species of recombinant horseradish peroxidase by using a P. pastoris platform strain in which OCH1 was deleted. This och1 knockout strain showed a growth impaired phenotype and considerable rearrangements of cell wall components, but nevertheless secreted more homogeneously glycosylated protein carrying mainly Man8 instead of Man10 N-glycans as a dominant core glycan structure at a volumetric productivity of 70% of the wildtype strain.

Microbials for the production of monoclonal antibodies and antibody fragments

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Glycosylated full length antibodies are currently produced in mammalian cells.

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Antibody fragments can be produced in microbial organisms.

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Strain engineering allows production of full length antibodies in microbials.

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Microbials provide several advantages over mammalian cells.

Monoclonal antibodies (mAbs) and antibody fragments represent the most important biopharmaceutical products today. Because full length antibodies are glycosylated, mammalian cells, which allow human-like N-glycosylation, are currently used for their production. However, mammalian cells have several drawbacks when it comes to bioprocessing and scale-up, resulting in long processing times and elevated costs. By contrast, antibody fragments, that are not glycosylated but still exhibit antigen binding properties, can be produced in microbial organisms, which are easy to manipulate and cultivate. In this review, we summarize recent advances in the expression systems, strain engineering, and production processes for the three main microbials used in antibody and antibody fragment production, namely Saccharomyces cerevisiae, Pichia pastoris, and Escherichia coli.

A dual-mode surface display system for the maturation and production of monoclonal antibodies in glyco-engineered Pichia pastoris

State-of-the-art monoclonal antibody (mAb) discovery methods that utilize surface display techniques in prokaryotic and eukaryotic cells require multiple steps of reformatting and switching of hosts to transition from display to expression. This results in a separation between antibody affinity maturation and full-length mAb production platforms. Here, we report for the first time, a method in Glyco-engineered Pichiapastoris that enables simultaneous surface display and secretion of full-length mAb molecules with human-like N-glycans using the same yeast cell. This paradigm takes advantage of homo-dimerization of the Fc portion of an IgG molecule to a surface-anchored "bait" Fc, which results in targeting functional “half” IgGs to the cell wall of Pichiapastoris without interfering with the secretion of full length mAb. We show the utility of this method in isolating high affinity, well-expressed anti-PCSK9 leads from a designed library that was created by mating yeasts containing either light chain or heavy chain IgG libraries. Coupled with Glyco-engineered Pichiapastoris, this method provides a powerful tool for the discovery and production of therapeutic human mAbs in the same host thus improving drug developability and potentially shortening the discovery time cycle.

Pichia pastoris: protein production host and model organism for biomedical research

Pichia pastoris is the most frequently used yeast system for heterologous protein production today. The last few years have seen several products based on this platform reach approval as biopharmaceutical drugs. Successful glycoengineering to humanize N-glycans is further fuelling this development. However, detailed understanding of the yeast’s physiology, genetics and regulation has only developed rapidly in the last few years since published genome sequences have become available. An expanding toolbox of genetic elements and strains for the improvement of protein production is being generated, including promoters, gene copy-number enhancement, gene knockout and high-throughput methods. Protein folding and secretion have been identified as significant bottlenecks in yeast expression systems, pinpointing a major target for strain optimization. At the same time, it has become obvious that P. pastoris, as an evolutionarily more ‘ancient’ yeast, may in some cases be a better model for human cell biology and disease than Saccharomyces cerevisiae.

A combined system for engineering glycosylation efficiency and glycan structure in Saccharomyces cerevisiae

We describe a novel synthetic N-glycosylation pathway to produce recombinant proteins carrying human-like N-glycans in Saccharomyces cerevisiae, at the same time addressing glycoform and glycosylation efficiency. The Δalg3 Δalg11 double mutant strain, in which the N-glycans are not matured to their native high-mannose structure, was used. In this mutant strain, lipid-linked Man(3)GlcNAc(2) is built up on the cytoplasmic side of the endoplasmic reticulum, flipped by an artificial flippase into the ER lumen, and then transferred with high efficiency to the nascent polypeptide by a protozoan oligosaccharyltransferase. Protein-bound Man(3)GlcNAc(2) serves directly as a substrate for Golgi apparatus-targeted human N-acetylglucosaminyltransferases I and II. Our results confirmed the presence of the complex human-like N-glycan structure GlcNAc(2)Man(3)GlcNAc(2) on the secreted monoclonal antibody HyHEL-10. However, due to the interference of Golgi apparatus-localized mannosyltransferases, heterogeneity of N-linked glycans was observed.

The expanding scope of DNA sequencing

In just seven years, next-generation technologies have reduced the cost and increased the speed of DNA sequencing by four orders of magnitude, and experiments requiring many millions of sequencing reads are now routine. In research, sequencing is being applied not only to assemble genomes and to investigate the genetic basis of human disease, but also to explore myriad phenomena in organismic and cellular biology. In the clinic, the utility of sequence data is being intensively evaluated in diverse contexts, including reproductive medicine, oncology and infectious disease. A recurrent theme in the development of new sequencing applications is the creative 'recombination' of existing experimental building blocks. However, there remain many potentially high-impact applications of next-generation DNA sequencing that are not yet fully realized.

Generation of diploid Pichia pastoris strains by mating and their application for recombinant protein production

Background

Yeast mating provides an efficient means for strain and library construction. However, biotechnological applications of mating in the methylotrophic yeast Pichia pastoris have been hampered because of concerns about strain stability of P. pastoris diploids. The aim of the study reported here is to investigate heterologous protein expression in diploid P. pastoris strains and to evaluate diploid strain stability using high cell density fermentation processes.

Results

By using a monoclonal antibody as a target protein, we demonstrate that recombinant protein production in both wild-type and glycoengineered P. pastoris diploids is stable and efficient during a nutrient rich shake flask cultivation. When diploid strains were cultivated under bioreactor conditions, sporulation was observed. Nevertheless, both wild-type and glycoengineered P. pastoris diploids showed robust productivity and secreted recombinant antibody of high quality. Specifically, the yeast culture maintained a diploid state for 240 h post-induction phase while protein titer and N-linked glycosylation profiles were comparable to that of a haploid strain expressing the same antibody. As an application of mating, we also constructed an antibody display library and used mating to generate novel full-length antibody sequences.

Conclusions

To the best of our knowledge, this study reports for the first time a comprehensive characterization of recombinant protein expression and fermentation using diploid P. pastoris strains. Data presented here support the use of mating for various applications including strain consolidation, variable-region glycosylation antibody display library, and process optimization.

The class I α1,2-mannosidases of Caenorhabditis elegans

During the biosynthesis of N-glycans in multicellular eukaryotes, glycans with the compositions Man(5)GlcNAc(2-3) are key intermediates. However, to reach this 'decision point', these N-glycans are first processed from Glc(3)Man(9)GlcNAc(2) through to Man(5)GlcNAc(2) by a number of glycosidases, whereby up to four α1-2-linked mannose residues are removed by class I mannosidases (glycohydrolase family 47). Whereas in the yeast Saccharomyces cerevisiae there are maximally three members of this protein family, in higher organisms there are multiple class I mannosidases residing in the endoplasmic reticulum and Golgi apparatus. The genome of the model nematode Caenorhabditis elegans encodes seven members of this protein family, whereby four are predicted to be classical processing mannosidases and three are related proteins with roles in quality control. In this study, cDNAs encoding the four predicted mannosidases were cloned and expressed in Pichia pastoris and the activity of these enzymes, designated MANS-1, MANS-2, MANS-3 and MANS-4, was verified. The first two can, dependent on the incubation time, remove three to four residues from Man(9)GlcNAc(2), whereas the action of the other two results in the appearance of the B isomer of Man(8)GlcNAc(2); together the complementary activities of these enzymes result in processing to Man(5)GlcNAc(2). With these data, another gap is closed in our understanding of the N-glycan biosynthesis pathway of the nematode worm.

A color-based stable multi-copy integrant selection system for Pichia pastoris using the attenuated ADE1 and ADE2 genes as auxotrophic markers

The methylotropic yeast Pichia pastoris has been used for more than two decades to successfully produce a large number of recombinant proteins. Currently, a wide variety of auxotrophic and drug based selection markers are employed to screen for clones expressing the protein of interest. For most proteins an increased copy number of the integrated plasmid results in higher levels of expression, but these multi-copy integrants can be unstable due to the propensity of P. pastoris for homologous recombination. Here we describe a multi-copy selection system based on ade1 and ade2 auxotrophic parent strains and the respective attenuated markers with truncated promoter regions. We show that for all four proteins we tested, the use of the attenuated markers leads to increased protein expression when compared with selection based on the full strength markers. The fact that the adenine auxotrophic strains grow more slowly than the complemented counterparts essentially ensures the stability of multi-copy integration. At the same time, the accumulation of a red dye in the auxotrophic strains also provides an easy, color-based selection for transformants with multiple copies.

Optimization of erythropoietin production with controlled glycosylation-PEGylated erythropoietin produced in glycoengineered Pichia pastoris

Pichia pastoris is a methylotropic yeast that has gained great importance as an organism for protein expression in recent years. Here, we report the expression of recombinant human erythropoietin (rhEPO) in glycoengineered P. pastoris. We show that glycosylation fidelity is maintained in fermentation volumes spanning six orders of magnitude and that the protein can be purified to high homogeneity. In order to increase the half-life of rhEPO, the purified protein was coupled to polyethylene glycol (PEG) and then compared to the currently marketed erythropoiesis stimulating agent, Aranesp(®) (darbepoetin). In in vitro cell proliferation assays the PEGylated protein was slightly, and the non-PEGylated protein was significantly more active than comparator. Pharmacodynamics as well as pharmacokinetic activity of PEGylated rhEPO in animals was comparable to that of Aranesp(®). Taken together, our results show that glycoengineered P. pastoris is a suitable production host for rhEPO, yielding an active biologic that is comparable to those produced in current mammalian host systems.