Production of humanized glycoproteins in bacteria and yeasts

Engineering strategies for enhanced heterologous protein production by Saccharomyces cerevisiae

Microbial proteins are promising substitutes for animal- and plant-based proteins. S. cerevisiae, a generally recognized as safe (GRAS) microorganism, has been frequently employed to generate heterologous proteins. However, constructing a universal yeast chassis for efficient protein production is still a challenge due to the varying properties of different proteins. With progress in synthetic biology, a multitude of molecular biology tools and metabolic engineering strategies have been employed to alleviate these issues. This review first analyses the advantages of protein production by S. cerevisiae. The most recent advances in improving heterologous protein yield are summarized and discussed in terms of protein hyperexpression systems, protein secretion engineering, glycosylation pathway engineering and systems metabolic engineering. Furthermore, the prospects for efficient and sustainable heterologous protein production by S. cerevisiae are also provided.

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.

Effects of Rho1, a small GTPase on the production of recombinant glycoproteins in Saccharomyces cerevisiae

Background

To humanize yeast N-glycosylation pathways, genes involved in yeast specific hyper-mannosylation must be disrupted followed by the introduction of genes catalyzing the synthesis, transport, and addition of human sugars. However, deletion of these genes, for instance, OCH1, which initiates hyper-mannosylation, could cause severe defects in cell growth, morphogenesis and response to environmental challenges.

Results

In this study, overexpression of RHO1, which encodes the Rho1p small GTPase, is confirmed to partially recover the growth defect of Saccharomyces cerevisiae Δalg3Δoch1 double mutant strain. In addition, transmission electron micrographs indicated that the cell wall structure of RHO1-expressed cells have an enhanced glucan layer and also a recovered mannoprotein layer, revealing the effect of Rho1p GTPase on cell wall biosynthesis. Similar complementation phenotypes have been confirmed by overexpression of the gene that encodes Fks2 protein, a catalytic subunit of a 1,3-β-glucan synthase. Besides the recovery of cell wall structure, the RHO1-overexpressed Δalg3Δoch1 strain also showed improved abilities in temperature tolerance, osmotic potential and drug sensitivity, which were not observed in the Δalg3Δoch1-FKS2 cells. Moreover, RHO1 overexpression could also increase N-glycan site occupancy and the amount of secreted glycoproteins.

Conclusions

Overexpression of RHO1 in ‘humanized’ glycoprotein producing yeasts could significantly facilitate its future industrial applications for the production of therapeutic glycoproteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0575-7) contains supplementary material, which is available to authorized users.

Immune recruitment or suppression by glycan engineering of endogenous and therapeutic antibodies

Human serum IgG contains multiple glycoforms which exhibit a range of binding properties to effector molecules such as cellular Fc receptors. Emerging knowledge of how the Fc glycans contribute to the antibody structure and effector functions has opened new avenues for the exploitation of defined antibody glycoforms in the treatment of diseases. Here, we review the structure and activity of antibody glycoforms and highlight developments in antibody glycoengineering by both the manipulation of the cellular glycosylation machinery and by chemoenzymatic synthesis. We discuss wide ranging applications of antibody glycoengineering in the treatment of cancer, autoimmunity and inflammation. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

Emerging technologies for making glycan-defined glycoproteins

Protein glycosylation is a common and complex posttranslational modification of proteins, which expands functional diversity while boosting structural heterogeneity. Glycoproteins, the end products of such a modification, are typically produced as mixtures of glycoforms possessing the same polypeptide backbone but differing in the site of glycosylation and/or in the structures of pendant glycans, from which single glycoforms are difficult to isolate. The urgent need for glycan-defined glycoproteins in both detailed structure-function relationship studies and therapeutic applications has stimulated an extensive interest in developing various methods for manipulating protein glycosylation. This review highlights emerging technologies that hold great promise in making a variety of glycan-defined glycoproteins, with a particular emphasis in the following three areas: specific glycoengineering of host biosynthetic pathways, in vitro chemoenzymatic glycosylation remodeling, and chemoselective and site-specific glycosylation of proteins.

Algae as protein factories: expression of a human antibody and the respective antigen in the diatom Phaeodactylum tricornutum

Microalgae are thought to offer great potential as expression system for various industrial, therapeutic and diagnostic recombinant proteins as they combine high growth rates with all benefits of eukaryotic expression systems. Moreover, microalgae exhibit a phototrophic lifestyle like land plants, hence protein expression is fuelled by photosynthesis, which is CO₂-neutral and involves only low production costs. So far, however, research on algal bioreactors for recombinant protein expression is very rare calling for further investigations in this highly promising field. In this study, we present data on the expression of a monoclonal human IgG antibody against the Hepatitis B surface protein and the respective antigen in the diatom Phaeodactylum tricornutum. Antibodies are fully-assembled and functional and accumulate to 8.7% of total soluble protein, which complies with 21 mg antibody per gram algal dry weight. The Hepatitis B surface protein is functional as well and is recognized by algae-produced and commercial antibodies.

Advances in the production and downstream processing of antibodies

Sales of monoclonal antibody (mAbs) therapies exceeded $ 40 billion in 2010 and are expected to reach $ 70 billion by 2015. The majority of the approved antibodies are targeting cancer and autoimmune diseases with the top 5 grossing antibodies populating these two areas. In addition over 100 monoclonal antibodies are in Phase II and III of clinical development and numerous others are in various pre-clinical and safety studies. Commercial production of monoclonal antibodies is one of the few biotechnology manufacturing areas that has undergone significant improvements and standardization over the last ten years. Platform technologies have been established based on the structural similarities of these molecules and the regulatory requirements. These improvements include better cell lines, advent of high-performing media free of animal-derived components, and advances in bioreactor and purification processes. In this chapter we will examine the progress made in antibody production as well as discuss the future of manufacturing for these molecules, including the emergence of single use technologies.

Expression of a recombinant elastin-like protein in pichia pastoris

The translation of highly repetitive gene sequences is often associated with reduced levels of protein expression and may be prone to mutational events. In this report, we describe a modified concatemerization strategy to construct a gene with enhanced sequence diversity that encodes a highly repetitive elastin-like protein polymer for expression in Pichia pastoris. Specifically, degenerate oligonucleotides were used to create a monomer library, which after concatemerization yielded a genetically nonrepetitive DNA sequence that encoded identical pentapeptide repeat sequences. By limiting genetic repetition, the risk of genetic deletions, rearrangements, or premature termination errors during protein synthesis is minimized.

Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy

During their development and administration, protein-based drugs routinely display suboptimal therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular strategies to improve the therapeutic behavior of protein drugs. Among the currently developed approaches, glycoengineering is one of the most promising, because it has been shown to simultaneously afford improvements in most of the parameters necessary for optimization of in vivo efficacy while allowing for targeting to the desired site of action. These include increased in vitro and in vivo molecular stability (due to reduced oxidation, cross-linking, pH-, chemical-, heating-, and freezing-induced unfolding/denaturation, precipitation, kinetic inactivation, and aggregation), as well as modulated pharmacodynamic responses (due to altered potencies from diminished in vitro enzymatic activities and altered receptor binding affinities) and improved pharmacokinetic profiles (due to altered absorption and distribution behaviors, longer circulation lifetimes, and decreased clearance rates). This article provides an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and describes the current understanding of the mechanisms by which glycosylation leads to such effects.

Heterologous expression of glucose oxidase in the yeast Kluyveromyces marxianus

BACKGROUND

In spite of its advantageous physiological properties for bioprocess applications, the use of the yeast Kluyveromyces marxianus as a host for heterologous protein production has been very limited, in constrast to its close relative Kluyveromyces lactis. In the present work, the model protein glucose oxidase (GOX) from Aspergillus niger was cloned into K. marxianus CBS 6556 and into K. lactis CBS 2359 using three different expression systems. We aimed at verifying how each expression system would affect protein expression, secretion/localization, post-translational modification, and biochemical properties.

RESULTS

The highest GOX expression levels (1552 units of secreted protein per gram dry cell weight) were achieved using an episomal system, in which the INU1 promoter and terminator were used to drive heterologous gene expression, together with the INU1 prepro sequence, which was employed to drive secretion of the enzyme. In all cases, GOX was mainly secreted, remaining either in the periplasmic space or in the culture supernatant. Whereas the use of genetic elements from Saccharomyces cerevisiae to drive heterologous protein expression led to higher expression levels in K. lactis than in K. marxianus, the use of INU1 genetic elements clearly led to the opposite result. The biochemical characterization of GOX confirmed the correct expression of the protein and showed that K. marxianus has a tendency to hyperglycosylate the protein, in a similar way as already observed for other yeasts, although this tendency seems to be smaller than the one of e.g. K. lactis and S. cerevisiae. Hyperglycosylation of GOX does not seem to affect its affinity for the substrate, nor its activity.

CONCLUSIONS

Taken together, our results indicate that K. marxianus is indeed a good host for the expression of heterologous proteins, not only for its physiological properties, but also because it correctly secretes and folds these proteins.

Localization of Golgi-resident glycosyltransferases

For many glycosyltransferases, the information that instructs Golgi localization is located within a relatively short sequence of amino acids in the N-termini of these proteins comprising: the cytoplasmic tail, the transmembrane spanning region, and the stem region (CTS). Also, one enzyme may be more reliant on a particular region in the CTS for its localization than another. The predominance of these integral membrane proteins in the Golgi has seen these enzymes become central players in the development of membrane trafficking models of transport within this organelle. It is now understood that the means by which the characteristic distributions of glycosyltransferases arise within the subcompartments of the Golgi is inextricably linked to the mechanisms that cells employ to direct the flow of proteins and lipids within this organelle.

Characterization of endoplasmic reticulum-localized UDP-D-galactose: hydroxyproline O-galactosyltransferase using synthetic peptide substrates in Arabidopsis

We characterized peptidyl hydroxyproline (Hyp) O-galactosyltransferase (HGT), which is the initial enzyme in the arabinogalactan biosynthetic pathway. An in vitro assay of HGT activity was established using chemically synthesized fluorescent peptides as acceptor substrates and extracts from Arabidopsis (Arabidopsis thaliana) T87 cells as a source of crude enzyme. The galactose residue transferred to the peptide could be detected by high-performance liquid chromatography and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analyses. HGT required a divalent cation of manganese for maximal activity and consumed UDP-D-galactose as a sugar donor. HGT exhibited an optimal pH range of pH 7.0 to 8.0 and an optimal temperature of 35 degrees C. The favorable substrates for the activity seemed to be peptides containing two alternating imino acid residues including at least one acceptor Hyp residue, although a peptide with single Hyp residue without any other imino acids also functioned as a substrate. The results of sucrose density gradient centrifugation revealed that the cellular localization of HGT activity is identical to those of endoplasmic reticulum markers such as Sec61 and Bip, indicating that HGT is predominantly localized to the endoplasmic reticulum. To our knowledge, this is the first characterization of HGT, and the data provide evidence that arabinogalactan biosynthesis occurs in the protein transport pathway.

Production of heterologous proteins using the fission-yeast (Schizosaccharomyces pombe) expression system

The fission yeast Schizosaccharomyces pombe is a particularly useful model for studying the function and regulation of genes from higher eukaryotes. The genome of Sc. pombe has been sequenced, and DNA microarray, proteome and transcriptome analyses have been carried out. Among the well-characterized yeast species, Sc. pombe is considered an attractive host for the production of heterologous proteins. Expression vectors for high-level expression in Sc. pombe have been developed and many foreign proteins have been successfully expressed. However, further improvements in the protein-expressing host systems are still required for the production of heterologous proteins involved in post-translational modification, metabolism and intracellular trafficking. This minireview focuses on recent advances in heterologous protein production by use of engineered fission-yeast strains.

Emerging methods for the production of homogeneous human glycoproteins

Most circulating human proteins exist as heterogeneously glycosylated variants (glycoforms) of an otherwise homogeneous polypeptide. Though glycan heterogeneity is most likely important to glycoprotein function, the preparation of homogeneous glycoforms is important both for the study of the consequences of glycosylation and for therapeutic purposes. This review details selected approaches to the production of homogeneous human N- and O-linked glycoproteins with human-type glycans. Particular emphasis is placed on recent developments in the engineering of glycosylation pathways within yeast and bacteria for in vivo production, and on the in vitro remodeling of glycoproteins by enzymatic means. The future of this field is very exciting.

Structure and synthesis of polyisoprenoids used in N-glycosylation across the three domains of life

N-linked protein glycosylation was originally thought to be specific to eukaryotes, but evidence of this post-translational modification has now been discovered across all domains of life: Eucarya, Bacteria, and Archaea. In all cases, the glycans are first assembled in a step-wise manner on a polyisoprenoid carrier lipid. At some stage of lipid-linked oligosaccharide synthesis, the glycan is flipped across a membrane. Subsequently, the completed glycan is transferred to specific asparagine residues on the protein of interest. Interestingly, though the N-glycosylation pathway seems to be conserved, the biosynthetic pathways of the polyisoprenoid carriers, the specific structures of the carriers, and the glycan residues added to the carriers vary widely. In this review we will elucidate how organisms in each basic domain of life synthesize the polyisoprenoids that they utilize for N-linked glycosylation and briefly discuss the subsequent modifications of the lipid to generate a lipid-linked oligosaccharide.