Synthesis and secretion of hepatitis B middle surface antigen by the methylotrophic yeast Hansenula polymorpha

Selective extraction of recombinant membrane proteins from Hansenula polymorpha by pulsed electric field and lytic enzyme pretreatment

BACKGROUND

In yeast, recombinant membrane proteins including viral scaffold proteins used for the formation of enveloped Virus-like particles (eVLPs) typically accumulate intracellularly. Their recovery is carried out by mechanical disruption of the cells, often in combination with detergent treatment. Cell permeabilization is an attractive alternative to mechanical lysis because it allows for milder and more selective recovery of different intracellular products.

RESULTS

Here, we present a novel approach for extraction of integral membrane proteins from yeast based on cell envelope permeabilization through a combination of pulsed electric field and lytic enzyme pretreatment of the cells. Our primary experiments focused on Hansenula polymorpha strain #25-5 co-expressing the integral membrane small surface protein (dS) of the duck hepatitis B virus and a fusion protein of dS with a trimer of a Human papillomavirus (HPV) L2-peptide (3xL2-dS). Irreversible plasma membrane permeabilization was induced by treating the cell suspension with monopolar rectangular pulses using a continuous flow system. The permeabilized cells were incubated with lyticase and dithiothreitol. This treatment increased the cell wall permeability, resulting in the release of over 50% of the soluble host proteins without causing significant cell lysis. The subsequent incubation with Triton X-100 resulted in the solubilization and release of a significant portion of 3xL2-dS and dS from the cells. By applying two steps: (i) brief heating of the cells before detergent treatment, and (ii) incubation of the extracts with KSCN, an 80% purity on the protein level has been achieved. Experiments performed with H. polymorpha strain T#3-3, co-expressing dS and the fusion protein EDIIIWNV-dS consisting of dS and the antigen from the West Nile virus (WSV), confirmed the applicability of this approach for recovering dS. The treatment, optimal for solubilization of 3xL2-dS and a significant part of dS, was not effective in isolating the fused protein EDIIIWNV-dS from the membranes, resulting in its retention within the cells.

CONCLUSIONS

This study presents an alternative approach for the recovery and partial purification of viral membrane proteins expressed in H. polymorpha. The factors influencing the effectiveness of this procedure and its potential use for the recovery of other integral membrane proteins are discussed.

Electroinduced Extraction of Human Ferritin Heavy Chain Expressed in Hansenula polymorpha

А protocol for the efficient and selective recovery of human ferritin heavy chain (FTH1) expressed intracellularly in Hansenula polymorpha was developed. It was based on electropermeabilisation and an increase in the cell wall porosity by pulsed electric field (PEF) treatment and subsequent incubation with a low concentration of a lytic enzyme. Irreversible plasma membrane permeabilisation was induced by applying rectangular electric pulses in the flow mode. The electrical treatment itself did not cause the release of the recombinant protein but induced the sensitisation of H. polymorpha cells to the lytic enzyme. Consequently, the subsequent incubation of the permeabilised cells with lyticase led to the recovery of approximately 90% of the recombinant protein, with a purification factor of 1.8. A similar efficiency was obtained by using the industrial lytic enzyme Glucanex. The released FTH1 appears in the form of an oligomer with a molecular mass of approximately 480 kDa, which is able to bind iron. The possibility for scaling the proposed protocol is discussed.

Revisiting the Cellulosimicrobium cellulans yeast-lytic beta-1,3-glucanases toolbox: a review

Cellulosimicrobium cellulans (also known with the synonyms Cellulomonas cellulans, Oerskovia xanthineolytica, and Arthrobacter luteus) is an actinomycete that excretes yeast cell wall lytic enzyme complexes containing endo-beta-1,3-glucanases [EC 3.2.1.39 and 3.2.1.6] as key constituents. Three genes encoding endo-beta-1,3-glucanases from two C. cellulans strains have been cloned and characterised over the past years. The betaglII and betaglIIA genes from strain DSM 10297 (also known as O. xanthineolytica LL G109) encoded proteins of 40.8 and 28.6 kDa, respectively, whereas the beta-1,3-glucanase gene from strain ATCC 21606 (also known as A. luteus 73-14) encoded a 54.5 kDa protein. Alignment of their deduced amino acid sequences reveal that betaglII and betaglIIA have catalytic domains assigned to family 16 of glycosyl hydrolases, whereas the catalytic domain from the 54.5 kDa glucanase belongs to family 64. Notably, both betaglII and the 54.5 kDa beta-1,3-glucanase are multidomain proteins, having a lectin-like C-terminal domain that has been assigned to family 13 of carbohydrate binding modules, and that confers to beta-1,3-glucanases the ability to lyse viable yeast cells. Furthermore, betaglII may also undergo posttranslational proteolytic processing of its C-terminal domain, resulting in a truncated enzyme retaining its glucanase activity but with very low yeast-lytic activity. In this review, the diversity in terms of structural and functional characteristics of the C. cellulans beta-1,3-glucanases has been compiled and compared.

Transfer and expression of heterologous genes in yeasts other than Saccharomyces cerevisiae

In the past few years, yeasts other than those belonging to the genus Saccharomyces have become increasingly important for industrial applications. Species such as Pichia pastoris, Hansenula polymorpha, Schizosaccharomyces pombe, Yarrowia lipolytica and Kluyveromyces lactis have been modified genetically and used for the production of heterologous proteins. For a number of additional yeasts such as Schwanniomyces occidentalis, Zygosaccharomyces rouxii, Trichosporon cutaneum, Pachysolen tannophilus, Pichia guilliermondii and members of the genus Candida genetic transformation systems have been worked out. Transformation was achieved using either dominant selection markers based on antibiotic resistance genes or auxotrophic markers in conjunction with cloned biosynthetic genes involved in amino acid or nucleotide metabolism.

Hepatitis B surface antigen (HBsAg) expression in plant cell culture: Kinetics of antigen accumulation in batch culture and its intracellular form

The production of edible vaccines in transgenic plants and plant cell culture may be improved through a better understanding of antigen processing and assembly. The hepatitis B surface antigen (HBsAg) was chosen for study because it undergoes substantial and complex post-translational modifications, which are necessary for its immunogenicity. This antigen was expressed in soybean (Glycine max L. Merr. cv Williams 82) and tobacco NT1 (Nicotiana tabacum L.) cell suspension cultures, and HBsAg production in batch culture was characterized. The plant-derived antigen consisted predominantly of disulfide cross-linked HBsAg protein (p24(s)) dimers, which were all membrane associated. Similar to yeast, the plant-expressed HBsAg was retained intracellularly. The maximal HBsAg titers were obtained with soybean suspension cultures (20-22 mg/L) with titers in tobacco cultures being approximately 10-fold lower. For soybean cells, electron microscopy and immunolocalization demonstrated that all the HBsAg was localized to the endoplasmic reticulum (ER) and provoked dilation and proliferation of the ER network. Sucrose gradient analysis of crude extracts showed that HBsAg had a complex size distribution uncharacteristic of the antigen's normal structure of uniform 22-nm virus-like particles. The extent of authentic epitope formation was assessed by comparing total p24(s) synthesized to that reactive by polyclonal and monoclonal immunoassays. Depending on culture age, between 40% and 100% of total p24(s) was polyclonal antibody reactive whereas between 6% and 37% was recognized by a commercial monoclonal antibody assay. Possible strategies to increase HBsAg production and improve post-translational processing are discussed.

Engineering of non-conventional yeasts for efficient synthesis of macromolecules: the methylotrophic genera

Methylotrophic yeasts, named after their ability to grow on methanol as the sole carbon source, have raised large interest as recombinant protein factories. In this review, we explain the basic mechanisms underlying this interest and describe the minimal requirements to transform the two genera recognized as methylotrophic, Pichia and Candida, into a powerful protein production tool. We present a comparison between this group of yeasts and the conventional yeasts used as expression system in view of productivity, level of secretion and quality of post-translational modifications. Selected examples of recombinant protein produced by methylotrophic yeast are also included.

The methylotrophic yeast Hansenula polymorpha: a versatile cell factory

The development of heterologous overexpression systems for soluble proteins has greatly advanced the study of the structure/function relationships of these proteins and their biotechnological and pharmaceutical applications. In this paper we present an overview on several aspects of the use of the methylotrophic yeast Hansenula polymorpha as a host for heterologous gene expression. H. polymorpha has been successfully exploited as a cell factory for the large-scale production of such components. Stable, engineered strains can be obtained by site-directed integration of expression cassettes into the genome, for which various constitutive and inducible promoters are available to control the expression of the foreign genes. New developments have now opened the way to additional applications of H. polymorpha, which are unprecedented for other organisms. Most importantly, it may be the organism of choice for reliable, large-scale production of heterologous membrane proteins, using inducible intracellular membranes and targeting sequences to specifically insert these proteins stably into these membranes. Furthermore, the use of H. polymorpha offers the possibility to accumulate the produced components into specific compartments, namely peroxisomes. These organelles are massively induced during growth of the organism on methanol and may occupy up to 80% of the cell volume. Accumulation inside peroxisomes prevents undesired modifications (e.g. proteolytic processing or glycosylation) and is also in particular advantageous when proteins are produced which are toxic or harmful for the host.

Application of yeasts in gene expression studies: a comparison of Saccharomyces cerevisiae, Hansenula polymorpha and Kluyveromyces lactis -- a review

From the onset of gene technology yeasts have been among the most commonly used host cells for the production of heterologous proteins. At the beginning of this new development the attention in molecular biology and biotechnology focused on the use of the best characterized species, Saccharomyces cerevisiae, leading to an increasing number of production systems for recombinant compounds. In recent years alternative yeasts became accessible for the techniques of modern molecular genetics and, thereby, for potential applications in biotechnology. In this respect Kluyveromyces lactis, and the methylotrophs Hansenula polymorpha and Pichia pastoris have been proven to offer significant advantages over the traditional baker's yeast for the production of certain proteins. In the following article, the present status of the various yeast systems is discussed.

Molecular cloning of a lytic beta-1,3-glucanase gene from Oerskovia xanthineolytica LLG109. A beta-1,3-glucanase able to selectively permeabilize the yeast cell wall

Molecular cloning of the beta gIII gene encoding for an endo-beta-1,3-glucanase (beta gl II) from Oerskovia xanthineolytica LLG109, a yeast-lytic gram-positive bacterium, has been conducted in order to elucidate its primary sequence and subsequently express it into B. subtilis. This endo-beta-1,3-glucanase exhibits low yeast-lytic activity toward viable S. cerevisiae cells, and it has shown ability to selectively permeabilize the yeast cell wall and release intracellular proteins produced by yeast. Highly degenerate oligonucleotides have been used to PCR-amplify a region of the beta-1,3-glucanase II encoding gene from O. xanthineolytica LLG109. The amplified fragment has been cloned and sequenced. The deduced amino acid sequence contains regions identical to the amino acid sequences previously determined by direct sequencing of the purified enzyme from O. xanthineolytica LLG109. By using the 180-bp PCR product as a homologous probe, we have been able to isolate four positive clones harboring plasmids pPF1A, pPF1B, pPF8A, and pPF9A, respectively, from a partial genomic library from O. xanthineolytica LLG109. All four plasmids contained a 2.7-kb BamHI insert that hybridized to the PCR probe under high stringency conditions. The 2.7-kb fragment seemed to be identical in all four cases regarding preliminary partial restriction mapping analysis done on the four plasmids. The 1.5-kb BamHI/KpnI restriction fragment from pPF8A and pPF9A hybridizing with the 180-bp PCR probe is presently being sequenced. The cloning of the lytic beta-1,3-glucanase from O. xanthineolytica LLG109 expands the number of yeast lytic beta-glucanases so far cloned. The availability of the nucleotide sequences of such a family of genes will allow further understanding of the role and mode of action of these enzymes in yeast cell wall degradation. In addition, a more extensive study on the structure and functional relationships of these enzymes will allow us to engineer "tailor-made" lytic beta-1,3-glucanases for use in new and improved large-scale selective cell permeabilization (SCP) and selective protein recovery (SPR) from yeast cells, not only from S. cerevisiae but also from alternative yeast expression systems such as Hansenula polymorpha, Pichia pastoris, and others, which are becoming of increasing importance in biotechnology.

Review: methylotrophic yeasts as factories for the production of foreign proteins

In this contribution we discuss the potential of methylotrophic yeasts as hosts for the high level production of valuable foreign proteins. Recent relevant achievements on the intracellular production or secretion of proteins are summarized. Special attention is paid to a specific advantage of the use of methylotrophic yeasts, namely the possibility of accumulating the foreign gene products inside peroxisomes. This approach may be of major advantage when the protein product is toxic for the host cell and, also, to protect these proteins from undesired side-effects such as proteolysis or aggregation.

Plasmid reorganization during integrative transformation in Hansenula polymorpha

During studies of integrative transformation in Hansenula polymorpha, it was found that transformants with plasmids possessing the LEU2 gene of H. polymorpha were frequently unstable and lost plasmids while growing on non-selective medium. These transformants possessed reorganized plasmids capable of replication in H. polymorpha. Two such plasmids were isolated and characterized. It was shown that they contain additional DNA segments which were not present in the original plasmid used for transformation. Southern hybridization analysis carried out with labeled DNA probes derived from these segments showed that they consisted of H. polymorpha DNA. The hybridization patterns indicated that corresponding sequences were homologous to several chromosomal regions. These chromosomal DNA segments apparently carried H. polymorpha autonomous replicating sequences (HARS), since plasmids bearing them could transform H. polymorpha with high efficiency and were maintained in transformants in an autonomous state. Sequence analysis of one such captured chromosomal fragment revealed several eight- to ten-base AT-rich blocks similar to the presumed HARS sequence defined by Roggenkamp et al. (1986). Analogous reorganization was also observed with respect to integrative plasmids carrying the TRP3 and HIS3 genes of H. polymorpha and the ADE2 gene of Saccharomyces cerevisiae as selectable markers.

Expression of the glucose oxidase gene from Aspergillus niger in Hansenula polymorpha and its use as a reporter gene to isolate regulatory mutations

The glucose oxidase gene (god) from Aspergillus niger was expressed in Hansenula polymorpha using the methanol oxidase promoter and transcription termination region and the MF-alpha leader sequence from Saccharomyces cerevisiae to direct secretion. The expression cassette was cloned into the S. cerevisiae vector YEp13 and used to transform H. polymorpha strain A16. In the initial transformants plasmid replication was unstable, but was stabilized by a growth regime consisting of alternating cycles of selective and non-selective growth. The stabilized strain was grown to high cell density by fed-batch fermentation. Upon induction of the MOX promoter, glucose oxidase synthesis was initiated. At the end of the fermentation, the culture density was 76 g dry weight/1 and 108 IU/ml (0.5 g/1 or 0.65% dry weight) glucose oxidase was found in the culture medium; a further 86 IU/ml (0.43 g/1 or 0.56% dry weight) was recovered from the cell lysate. A plate assay was used to monitor glucose oxidase levels in individual colonies. This was then used to isolate mutants which showed abnormal regulation of god expression or which showed an altered pattern of secretion. One mutant, which showed increased production of glucose oxidase, was grown to high cell density by fed-batch fermentation (100.6 g/l) and produced 445 IU/ml(2.25 g/l or 2.2% dry weight) extracellularly and 76 IU/ml (0.38 g/l or 0.4% dry weight) intracellularly. The mutant thus not only increased total production but exported 83% of the total enzyme made compared to 55% in the parent strain.

Conversion of starch to ethanol in a recombinant Saccharomyces cerevisiae strain expressing rice alpha-amylase from a novel Pichia pastoris alcohol oxidase promoter

A recombinant Saccharomyces cerevisiae, expressing and secreting rice alpha-amylase, converts starch to ethanol. The rice alpha-amylase gene (OS103) was placed under the transcriptional control of the promoter from a newly described Pichia pastoris alcohol oxidase genomic clone. The nucleotide sequences of ZZA1 and other methanol-regulated promoters were analyzed. A highly conserved sequence (TTG-N3-GCTTCCAA-N5-TGGT) was found in the 5' flanking regions of alcohol oxidase, methanol oxidase, and dihydroxyacetone synthase genes in Pichia pastoris, Hansenula polymorpha, and Candida boidinii S2. The yeast strain containing the ZZA1-OS103 fusion secreted biologically active enzyme into the culture media while fermenting soluble starch.

Immunoelectron microscopic detection of the hepatitis B virus major surface protein in dilated perinuclear membranes of yeast cells

The major surface protein of hepatitis B virus produced in Saccharomyces cerevisiae can be recovered from cell lysates in the form of 22-mm lipoprotein particles. Immunoelectron microscopy was applied to investigate site and time of particle assembly. Thin sections of yeast cells revealed that production of the S protein provoked a dilation of the endoplasmic reticulum. Dilated areas were specifically labeled with a polyclonal antibody raised against glutaraldehyde-treated yeast-derived HBsAg particles. In contrast to previous postulates of particle formation during cell lysis and extract preparation, these results suggest that particle formation in yeast occurs in the endoplasmic reticulum and that transport of particles along the secretion pathway is blocked.

Heterologous protein production in yeast

The exploitation of recombinant DNA technology to engineer expression systems for heterologous proteins represented a major task within the field of biotechnology during the last decade. Yeasts attracted the attention of molecular biologists because of properties most favourable for their use as hosts in heterologous protein production. Yeasts follow the general eukaryotic posttranslational modification pattern of expressed polypeptides, exhibit the ability to secrete heterologous proteins and benefit from an established fermentation technology. Aside from the baker's yeast Saccharomyces cerevisiae, an increasing number of alternative non-Saccharomyces yeast species are used as expression systems in basic research and for an industrial application. In the following review a selection from the different yeast systems is described and compared.

Some factors influencing the proportion of periplasmic hepatitisB virus pre-S2 antigen in the recombinant yeastHansenula polymorpha

A central composite design (CCD) was used to evaluate, for the purpose of future process optimization, the influence of pH, yeast extract and ammonium chloride concentrations on the proportion of periplasmic hepatitis B pre-S2 antigen in the recombinant yeast Hansenula polymorpha. Each factor was tested at five levels, and a second order polynomial model for the proportion of periplasmic antigen was fitted to the treatment combinations. pH showed the greatest effect: the proportion of periplasmic antigen was greatly increased at the higher pH levels. At the higher pH levels used, the proportion of periplasmic antigen was enhanced by a high concentration of ammonium chloride. Additional experiments have confirmed both the validity of the selected model and the optimal conditions found. A significant correlation was found between the proportion of periplasmic antigen and the total yield of antigen. These results indicated that it should be possible to modulate the distribution of the pre-S2 antigen between the periplasm and the cytoplasm of the yeast.

Yeast systems for the commercial production of heterologous proteins

Yeasts are attractive hosts for the production of heterologous proteins. Unlike prokaryotic systems, their eukaryotic subcellular organization enables them to carry out many of the post-translational folding, processing and modification events required to produce "authentic" and bioactive mammalian proteins. In addition, they retain the advantages of a unicellular microorganism, with respect to rapid growth and ease of genetic manipulation. The vast majority of yeast expression work has focused on the well-characterized baker's yeast Saccharomyces cerevisiae. However, with the development of DNA transformation technologies, a growing number of non-Saccharomyces yeasts are becoming available as hosts for recombinant polypeptide production. These include Hansenula polymorpha, Kluyveromyces lactis, Pichia pastoris, Schizosaccharomyces pombe, Schwanniomyces occidentalis and Yarrowia lipolytica. The performance of these alternative yeast expression systems is reviewed here relative to S. cerevisiae, and the advantages and limitations of these systems are discussed.

Fermentation study for the production of hepatitis B virus pre-S2 antigen by the methylotrophic yeastHansenula polymorpha

Various physico-chemical parameters have been studied in order to improve the production of hepatitis B virus pre-S2 antigen (middle surface antigen) by the methylotrophic yeast Hansenula polymorpha. Antigen production was done in two steps: first, production of cells on glycerol (Phase 1), followed by induction of antigen expression with methanol (Phase 2). Dense cultures of H. polymorpha, equivalent to 35-40 g/l (dry weight), were readily obtained in small fermenters using minimal medium containing glycerol as carbon source. Antigen expression in this minimal medium, after induction with methanol, was however, low and never exceeded 1.6 mg/l of culture. Antigen production was greatly enhanced by adding complex organic nitrogen sources along with methanol at induction time; yeast extract was the best of all the sources tested. In shake flasks, antigen production was proportional to yeast extract concentration up to 7% (w/v) yeast extract, it became clear the the nutritional conditions for good antigen expression were different from those for good biomass production. The effects of yeast extract were reproduced in small fermenters: antigen levels reached 8-9 mg/l in medium containing 6% (w/v) yeast extract during induction with methanol. The mechanisms of yeast extract's effects are still unknown but are probably nutritional. The recombinant H. polymorpha strain produced both periplasmic and intracellular antigen. The periplasmic antigen was shown to be present as 20-22-nm particles and was therefore immunogenic. Immunoblotting indicated that part of the pre-S2 antigen was present as a 24-kDa degradation product. These studies have led to a 140-fold increase in volumetric productivity of antigen and to a 4.6-fold increase in specific production.

Simultaneous expression of the S and L surface antigens of hepatitis B, and formation of mixed particles in the methylotrophic yeast, Hansenula polymorpha

An expression system has been developed for the methylotrophic yeast Hansenula polymorpha and used to co-express both the L (preS1-S2-S) and S hepatitis B surface antigens (HBsAg) under the control of strong methanol-inducible promoters derived from the methanol oxidase and from the formate dehydrogenase genes. A unique feature of this H. polymorpha expression system is the possibility of integrating up to 100 copies of an expression cassette via a multimeric integration mechanism. Several multimeric integrants containing various numbers of L and S expression cassettes were constructed to give a spectrum of strains characterized by different L to S ratios. The expression level of S antigen was 5-8% of the total soluble cell protein. Analysis by sucrose and CsCl density gradient centrifugation and by particle-specific immunoassays demonstrated that the synthesized HBsAg spontaneously assembled into composite subviral particles containing both S and L proteins. Only a minor portion of the L protein was found to be glycosylated. These H polymorpha-derived composite particles can be used for the production of a hepatitis B virus vaccine with the potential for improved immunogenicity due to the presence of a wider spectrum of epitopes and negligible glycosylation.