Host For Protein Expression Research Articles

A Novel Potential Signal Peptide Sequence and Overexpression of ER-Resident Chaperones Enhance Heterologous Protein Secretion in Thermotolerant Methylotrophic Yeast Ogataea thermomethanolica.

The thermotolerant methylotrophic yeast Ogataea thermomethanolica is a host for heterologous protein expression via secretion to the culture medium. Efficient secretion is a major bottleneck for heterologous protein production in this strain. To improve protein secretion, we explored whether the use of a native signal peptide sequence for directing heterologous protein secretion and overexpression of native ER-resident chaperone genes could improve heterologous protein secretion in O. thermomethanolica. We cloned and characterized genes encoding α-mating factor (Otα-MF) and ER-resident chaperones OtBiP, OtCNE1, and OtPDI. The pre and pre-pro sequences of Otα-MF were shown to promote higher secretion of heterologous endoxylanase comparing with the classical pre-pro sequence of Saccharomyces cerevisiae. However, in the case of heterologous glycosylated phytase, only the Otα-MF pre-pro sequence significantly enhanced protein secretion. The effect of chaperone overexpression on heterologous protein secretion was tested in cotransformant cells of O. thermomethanolica. Overexpression of ER-resident chaperones improved protein secretion depending on heterologous protein. Overexpression of OtBiP, OtCNE1, and OtPDI significantly increased unglycosylated endoxylanase secretion at both 30 and 37°C while only OtBiP overexpression enhanced glycosylated phytase secretion at 30°C. These observations suggested the possibility to improve heterologous protein secretion in O. thermomethanolica.

Factors Affecting Inducible Expression of Outer Membrane Protein A (OmpA) of Shigella dysenteriae Type-1 in Lactococcus lactis Using Nisin Inducible Controlled Expression (NICE).

Potential use of Lactococcus lactis (L. lactis) as a heterologous protein expression host as well as for delivery of multiple therapeutic proteins has been investigated extensively using Nisin Inducible Controlled Expression (NICE) system. Optimum inducible expression of heterologous protein by NICE system in L. lactis depends on multiple factors. To study the unexplored role of factors affecting heterologous protein expression in L. lactis using NICE, the present study outlines the optimization of various key parameters such as inducer concentration, host's proteases and precipitating agent using Outer membrane protein A (OmpA). For efficient expression and secretion of OmpA, pSEC:OmpA vector was successfully constructed. To circumvent the troubles encountered during detection of expressed OmpA, the precipitating agent was switched from TCA to methanol. Nevertheless, detection was achieved accompanied by degraded protein products. Speculating the accountability of observed degradation at higher inducer concentration, different nisin concentrations were evaluated. Lower nisin concentrations were found desirable for optimum expression of OmpA. Consistently observed degradation was eliminated by incorporation of protease inhibitor cocktail which inhibits intracellular proteases and expression in VEL1153 (NZ9000 ΔhtrA) strain which inhibits extracellular protease leading to optimum expression of OmpA. Versatility and complexity of NICE system in L. lactis requires fine-tuning of target protein specific parameters for optimum expression.

Investigation into the misincorporation of norleucine into a recombinant protein vaccine candidate.

A high level of norleucine misincorporation was detected in a recombinant methionine-rich protein vaccine candidate expressed in E. coli K12. An investigation was conducted to evaluate a simple remediation strategy to reduce norleucine misincorporation and to determine if the phenomenon was either (a) due to the depletion of methionine during fermentation, (b) a result of the cultivation environment, or (c) a strain-specific effect. While supplementation with exogenous methionine improved product quality, the undesirable biosynthesis of non-standard amino acids such as norleucine and norvaline persisted. In contrast, non-standard amino acid biosynthesis was quickly minimized upon selection of an appropriate fed-batch process control strategy, fermentation medium, and nutrient feed. By expressing the same protein in E. coli BL21(DE3), it was determined that the biosynthesis of norleucine and norvaline, and the misincorporation of norleucine into the protein were primarily attributed to the use of E. coli K12 as the host for protein expression.

Expression of enzymes for the usage in food and feed industry with Pichia pastoris

The methylotrophic yeast Pichia pastoris is an established protein expression host for the production of industrial enzymes. This yeast can be grown to very high cell densities and produces high titers of recombinant protein, which can be expressed intercellularly or be secreted to the fermentation medium. P. pastoris offers some advantages over other established expression systems especially in protein maturation. In food and feed production many enzymatically catalyzed processes are reported and the demand for new enzymes grows continuously. For instance the unique catalytic properties of enzymes are used to improve resource efficiency, maintain quality, functionalize food, and to prevent off-flavors. This review aims to provide an overview on recent developments in heterologous production of enzymes with P. pastoris and their application within the food sector.

Proteomic analysis and genome annotation of Pichia pastoris, a recombinant protein expression host.

Pichia pastoris is a widely used eukaryotic host for production of recombinant proteins. We performed a proteogenomic analysis using high resolution Fourier transform MS to characterize the proteome of the GS115 strain. Our analysis resulted in identification of 46,889 unique peptides mapping to 3914 unique protein groups, which corresponds to ∼ 80% of the predicted genes. In addition, our proteogenomic analysis led to the discovery of 64 novel genes and correction of 11 predicted gene models. The strategy used here demonstrates the utility of high resolution MS-derived peptide sequence data to cover near complete proteomes of organisms. Given the popularity of P. pastoris as a protein expression host, this proteome map should provide a list of contaminants derived from the host to assist in optimization of heterologous protein production. All MS data have been deposited in the ProteomeXchange with identifier PXD000627 (http://proteomecentral.proteomexchange.org/dataset/PXD000627).

Overcoming the solubility problem in E. coli: available approaches for recombinant protein production.

Despite the importance of recombinant protein production in academy and industrial fields, many issues concerning the expression of soluble and homogeneous product are still unsolved. Although several strategies were developed to overcome these obstacles, at present there is no magic bullet that can be applied for all cases. Indeed, several key expression parameters need to be evaluated for each protein. Among the different hosts for protein expression, Escherichia coli is by far the most widely used. In this chapter, we review many of the different tools employed to circumvent protein insolubility problems.

Characterization of an N-glycosylated Bacillus subtilis leucine aminopeptidase expressed in Pichia pastoris.

Aminopeptidase is an important flavorsome especially in protein hydrolysate debittering by removing hydrophobic amino acid residue at the N-terminal end. Besides, it is also applied to preparation of active peptides and analysis of protein sequence. In this study, leucine aminopeptidase from Bacillus subtilis was cloned and expressed in Pichia pastoris, a widely used heterologous protein expression host. Then it was purified and characterized. After methanol induction for 96 h, the aminopeptidase activity in culture supernatant reached 28.4 U ml(À1) , which was 7.1 times that of wild strain B. subtilis Zj016. The optimal temperature and pH of the purified recombinant enzyme were 60 °C and 8.5, respectively. The purified aminopeptidase was stable within 30-60 °C and pH 8.0-9.0. It was intensively inhibited by Ni(2β) , Ca(2β) , DL-dithiothreitol (DTT) and ethylene diamine tetraacetic acid (EDTA), but activated by Co(2β) . The Km toward leucine-p-nitroanilines (Leu-pNA) of the enzyme was 0.97 mM. The sequence analysis of aminopeptidase indicated three potential N-glycosylation sites and it was further verified via MALDI-TOF-MS analysis. Consequently, the N-glycosylated aminopeptidase exhibited higher thermostability and catalytic efficiency. The purified enzyme exhibited two bands through sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) while a single band can be identified when the enzyme was deglycosylated. Circular dichroism spectroscopy indicated that the secondary structure of recombinant aminopeptidase was similar to the wild-type.

Cloning and expression of Aspergillus flavus urate oxidase in Pichia pastoris.

Urate oxidase is an important enzyme with therapeutic and diagnostic applications. Rasburicase is a recombinant urate oxidase enzyme approved by FDA to use in the treatment of hyperuricemia conditions. Various hosts such as Saccharomyces cerevisiae, Hansenula polymorpha and Escherichia coli have been used to express the enzyme. Today, Pichia pastoris is considered as an important host for heterologous protein expression since it has beneficial characteristics such as strong promoters, simple scale up, post translational modifications, high cell density cultivation and simple genetic manipulation. In this study, Aspergillus flavus urate oxidase gene was cloned in pPICZαA expression vector and expressed in P. pastoris. The recombinant urate oxidase was expressed in secretory form and was confirmed through RT-PCR, SDS-PAGE analysis and western blotting. The enzyme activity was determined using a colorimetric assay. A production yield of 0.43 U/ml of culture supernatant was obtained.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-395) contains supplementary material, which is available to authorized users.

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.

Photosynthetic biomanufacturing in green algae; production of recombinant proteins for industrial, nutritional, and medical uses

Recombinant proteins are widely used for industrial, nutritional, and medical applications. Green microalgae have attracted considerable attention recently as a biomanufacturing platform for the production of recombinant proteins for a number of reasons. These photosynthetic eukaryotic microorganisms are safe, scalable, easy to genetically modify through transformation, mutagenesis, or breeding, and inexpensive to grow. Many microalgae species are genetically transformable, but the green alga Chlamydomonas reinhardtii is the most widely used host for recombinant protein expression. An extensive suite of molecular genetic tools has been developed for C. reinhardtii over the last 25 years, including a fully sequenced genome, well-established methods for transformation, mutagenesis and breeding, and transformation vectors for high levels of recombinant protein accumulation and secretion. Here, we review recent successes in the development of C. reinhardtii as a biomanufacturing host for recombinant proteins, including antibodies and immunotoxins, hormones, industrial enzymes, an orally-active colostral protein for gastrointestinal health, and subunit vaccines. In addition, we review the biomanufacturing potential of other green algae from the genera Dunaliella and Chlorella.

Expression of single-chain variable fragments fused with the Fc-region of rabbit IgG in Leishmania tarentolae

BackgroundIn recent years the generation of antibodies by recombinant methods, such as phage display technology, has increased the speed by which antibodies can be obtained. However, in some cases when recombinant antibodies have to be validated, expression in E. coli can be problematic. This primarily occurs when codon usage or protein folding of specific antibody fragments is incompatible with the E. coli translation and folding machinery, for instance when recombinant antibody formats that include the Fc-region are needed. In such cases other expression systems can be used, including the protozoan parasite Leishmania tarentolae (L. tarentolae). This novel host for recombinant protein expression has recently shown promising properties for the expression of single-chain antibody fragments. We have utilised the L. tarentolae T7-TR system to achieve expression and secretion of two scFvs fused to the Fc-region of rabbit immunoglobulin G (IgG).ResultsBased on the commercial vector pLEXSY_IE-blecherry4 (Jena Bioscience; Cat. No. EGE-255), we generated a vector containing the Fragment Crystallisable (Fc) region of rabbit IgG allowing insertions of single chain antibody fragments (scFvs) in frame via Ncol/Notl cloning (pMJ_LEXSY-rFc). For the expression of rabbit Fc-fusion scFvs (scFv-rFc) we cloned two scFvs binding to human vimentin (LOB7 scFv) and murine laminin (A10 scFv) respectively, into the modified vector. The LOB7-rFc and A10-rFc fusions expressed at levels up to 2.95 mg/L in L. tarentolae T7-TR. Both scFv-rFcs were purified from the culture supernatants using protein A affinity chromatography. Additionally, we expressed three different scFvs without the rFc regions using a similar expression cassette, obtaining yields up to 1.00 mg/L.ConclusionsTo our knowledge, this is the first time that antibody fragments with intact Fc-region of immunoglobulin have been produced in L. tarentolae. Using the plasmid pMJ_LEXSY-rFc, L. tarentolae T7-TR can be applied as an efficient tool for expression of rFc fusion antibody fragments, allowing easy purification from the growth medium. This system provides an alternative in cases where antibody constructs express poorly in standard prokaryotic systems. Furthermore, in cases where bivalent Fc-fused antibody constructs are needed, using L. tarentolae for expression provides an efficient alternative to mammalian expression.

Heterologous Expression of Mycobacterial Esx Complexes in Escherichia coli for Structural Studies Is Facilitated by the Use of Maltose Binding Protein Fusions

The expression of heteroligomeric protein complexes for structural studies often requires a special coexpression strategy. The reason is that the solubility and proper folding of each subunit of the complex requires physical association with other subunits of the complex. The genomes of pathogenic mycobacteria encode many small protein complexes, implicated in bacterial fitness and pathogenicity, whose characterization may be further complicated by insolubility upon expression in Escherichia coli, the most common heterologous protein expression host. As protein fusions have been shown to dramatically affect the solubility of the proteins to which they are fused, we evaluated the ability of maltose binding protein fusions to produce mycobacterial Esx protein complexes. A single plasmid expression strategy using an N-terminal maltose binding protein fusion to the CFP-10 homolog proved effective in producing soluble Esx protein complexes, as determined by a small-scale expression and affinity purification screen, and coupled with intracellular proteolytic cleavage of the maltose binding protein moiety produced protein complexes of sufficient purity for structural studies. In comparison, the expression of complexes with hexahistidine affinity tags alone on the CFP-10 subunits failed to express in amounts sufficient for biochemical characterization. Using this strategy, six mycobacterial Esx complexes were expressed, purified to homogeneity, and subjected to crystallization screening and the crystal structures of the Mycobacterium abscessus EsxEF, M. smegmatis EsxGH, and M. tuberculosis EsxOP complexes were determined. Maltose binding protein fusions are thus an effective method for production of Esx complexes and this strategy may be applicable for production of other protein complexes.

Use of Aspergillus niger β-glucosidase II gene (bglII) promoter elements to construct an efficient expression vector

Aspergillus niger is widely used as a homologous and heterologous protein expression host in the food industry. Therefore, there is an emergent need to construct a highly efficient expression vector. The promoter region encoding the β-glucosidase II (GQ471881) was evaluated. Specifically, two CCAAT-box, one CREA, and one AREA sequence located at −343 to −339nt, −159 to −155nt, −226 to −221nt, and −63 to −60nt (relative to the start codon of the bglII gene), respectively, were studied. The function of these consensus sequences was investigated by deletion analysis of the bglII promoter fused with the uidA gene (β-glucuronidase, GUS) as reporter. The GUS specific activity of the transformant, containing the hole region (−402 to −1) of the promoter sequence pBARGEM7-2-GUS-ANUT(d0), was 189U/mg. Moreover, the transformant pBARGEM7-2-GUS-ANUT3 (d3), containing −189 to −1 bglII gene promoter region, produced the highest GUS specific activity, 448U/mg. Because transformant d3 did not contain the CREA, it was free from carbon catabolite repression. This promoter has the potential to be an expression vector for application to the food industry.

Construction of a plasmid for heterologous protein expression with a constitutive promoter in Trichoderma reesei

Trichoderma reesei is widely used as a host for homologus and heterologus protein expression because of its well-known capability of protein secretion, especially cellulases secretion. In this study, a binary vector which could be used for protein expression was constructed with a constitutive promoter of rp2 gene. This vector contained the expression cassette Prp2-target gene-Trp2 and hygromycin B selection marker based on pCAMBIA1300 for T-DNA random insertion. The feasibility of the promoter was determined by eGFP (enhanced green fluorescence protein) expression in T. reesei. For heterologus protein expression, the expression of bgla from Aspergillus niger in the transformant was 3 folds higher than that of the wild type strain. The results demonstrate that this constitutive promoter could be applied for protein expression and thus this protein express system may contribute to the industrial protein production.

Directed Evolution of Clostridium phytofermentans Glycoside Hydrolase Family 9 Endoglucanase for Enhanced Specific Activity on Solid Cellulosic Substrate

Increasing specific activity of cellulase on solid cellulosic materials would be among the top priorities for second-generation biorefineries. However, the complicated relationship among the heterogeneity of solid cellulosic materials and different action mode cellulase components results in great challenges in cellulase engineering. We applied directed evolution to a Clostridium phytofermentans ISDg glycoside hydrolase family 9 processive endoglucanase (CpCel9) for enhanced hydrolytic performance by using Bacillus subtilis as a host for cloning and expression. Several CpCel9 mutants with both increased expression level and enhanced specific activity on the solid cellulosic material were obtained. The most active mutant, which also exhibits an increased expression level, had more than threefold specific activity than that of wild type on regenerated amorphous cellulose. Most mutation sites were located in the family 3 cellulose-binding module near to its catalytic module, which might guide the entrance of glucan into the catalytic module. This study suggested that directed evolution by combining B. subtilis secretory protein expression host and solid cellulosic substrates would be a powerful tool to evolve more active cellulase mutants for cost-effective biosaccharification process.

Comparative performance of S-adenosyl-l-methionine biosynthesis and degradation in Pichia pastoris using different promoters and novel consumption inhibitors

The yeast Pichia pastoris is a widely used host for recombinant protein expression, and has recently been engineered for whole-cell biocatalysis. The inducible PAOX and constitutive PGAP promoters are commonly employed. In this study, the S-adenosyl-l-methionine (SAM) biosynthesis and degradation efficiency of two P. pastoris strains were compared, and novel inhibitors that suppress SAM degradation were characterized. The strains exhibited clear physiological differences. PGAP-Pichia showed higher transcription and activity of SAM synthetase, and the rapid cell growth led to higher levels of spermidine synthesis from SAM. In contrast, PAOX-Pichia synthesized higher levels of glutathione from SAM, and this strain responded to hydrogen peroxide formation during methanol utilization. Aristeromycin proved an efficient inhibitor of SAM degradation in PAOX-Pichia; 0.02mg/L led to a 36.36% reduction in the ratio of glutathionine:SAM, and SAM accumulation was enhanced by 7.74% to 11.83g/L. Ethanol was an even more efficient inhibitor of SAM consumption in PGAP-Pichia; 8g/L resulted in a 73.68% decrease in the ratio of SPD:SAM, and SAM production was elevated by 54.55% to 0.17g/L/h.

Autoxidation and Oxygen Binding Properties of Recombinant Hemoglobins with Substitutions at the αVal-62 or βVal-67 Position of the Distal Heme Pocket

The E11 valine in the distal heme pocket of either the α- or β-subunit of human adult hemoglobin (Hb A) was replaced by leucine, isoleucine, or phenylalanine. Recombinant proteins were expressed in Escherichia coli and purified for structural and functional studies. (1)H NMR spectra were obtained for the CO and deoxy forms of Hb A and the mutants. The mutations did not disturb the α1β2 interface in either form, whereas the H-bond between αHis-103 and βGln-131 in the α1β1 interfaces of the deoxy α-subunit mutants was weakened. Localized structural changes in the mutated heme pocket were detected for the CO form of recombinant Hb (rHb) (αV62F), rHb (βV67I), and rHb (βV67F) compared with Hb A. In the deoxy form the proximal histidyl residue in the β-subunit of rHb (βV67F) has been altered. Furthermore, the interactions between the porphyrin ring and heme pocket residues have been perturbed in rHb (αV62I), rHb (αV62F), and rHb (βV67F). Functionally, the oxygen binding affinity (P50), cooperativity (n50), and the alkaline Bohr Effect of the three α-subunit mutants and rHb (βV67L) are similar to those of Hb A. rHb (βV67I) and rHb (βV67F) exhibit low and high oxygen affinity, respectively. rHb (βV67F) has P50 values lower that those reported for rHb (αL29F), a B10 mutant studied previously in our laboratory (Wiltrout, M. E., Giovannelli, J. L., Simplaceanu, V., Lukin, J. A., Ho, N. T., and Ho, C. (2005) Biochemistry 44, 7207-7217). These E11 mutations do not slow down the autoxidation and azide-induced oxidation rates of the recombinant proteins. Results from this study provide new insights into the roles of E11 mutants in the structure-function relationship in hemoglobin.

Expression of a truncated hepatitis E virus capsid protein in the protozoan organism Leishmania tarentolae and its application in a serological assay

Zoonotic infections with hepatitis E virus (HEV) genotype 3 are presumably transmitted via contaminated pig meat products, which raises the necessity for enhanced serological surveillance of pig herds. The aim of the study was to set up a novel protein expression system to overcome the well-known problems in (HEV-) protein expression using the standard Escherichia coli tools such as inclusion body formation and loss of protein conformation. A recombinant strain of the protozoan organism Leishmania tarentolae (L. tarentolae) was therefore established. A fragment of HEV ORF2 coding for a truncated capsid protein of a porcine HEV strain was cloned and parts of the plasmid DNA were introduced into the Leishmania genome, resulting in stably transformed cells. Via a C-terminal His-tag the recombinant HEVΔORF2 protein could be purified and concentrated directly from the medium, resulting in a total protein amount of approximately 1.4mg/l Leishmania culture. The recombinant protein was coated on ELISA plates and was proven to be highly reactive and well-suited to be applied in a serological assay. By investigating 144 porcine sera, the in-house assay detected specific antibodies in 43.1% of the samples and demonstrated a higher sensitivity than a commercially available antibody test. Taken together, it was shown that L. tarentolae exhibits a remarkable alternative expression strategy for viral antigens with considerable advantages of a eukaryotic protein expression host.

Stable expression plasmids for Streptomyces based on a toxin-antitoxin system

BackgroundBacteria included in the genus Streptomyces exhibit several attractive characteristics that make them adequate hosts for the heterologous expression of proteins. One of them is that some of its species have a high secretion capacity and hence the protein of interest could be released to the culture supernatant, facilitating downstream processing. To date, all the expression vectors described for these bacteria contain antibiotic resistance genes as selection markers. However, the use of antibiotics to produce proteins at industrial level is currently becoming more restricted owing to the possibility of contamination of the final product. In this report, we describe the use of the S. lividans yefM/yoeBsl toxin-antitoxin system to develop a stable plasmid expression system.ResultsIn order to use the yefM/yoeBsl system to stabilize expression plasmids in Streptomyces, a S. lividans mutant strain that contained only the toxin gene (yoeBsl) in its genome and the antitoxin gene (yefMsl) located in a temperature-sensitive plasmid was constructed and used as host. This strain was transformed with an expression plasmid harbouring both the antitoxin gene and the gene encoding the protein of interest. Thus, after elimination of the temperature-sensitive plasmid, only cells with the expression plasmid were able to survive. On using this system, two proteins - an α-amylase from S. griseus and a xylanase from S. halstedii - were overproduced without the addition of antibiotic to the culture medium. The production of both proteins was high, even after long incubations (8 days), and after serial subcultures, confirming the stability of the plasmids without antibiotic selection.ConclusionsThis is the first report that describes the use of a toxin-antitoxin system to maintain high -copy plasmids in Streptomyces. This finding could be a valuable tool for using Streptomyces as a host to produce proteins at the industrial and pharmaceutical levels without the use of antibiotics in the production step.

Use of Human Serum Albumin Fusion Tags for Recombinant Protein Secretory Expression in the Methylotrophic Yeast Hansenula polymorpha

The thermotolerant methylotrophic yeast Hansenula polymorpha is an attractive model organism for various fundamental studies, such as the genetic control of enzymes involved in methanol metabolism, peroxisome biogenesis, nitrate assimilation, and resistance to heavy metals and oxidative stresses. In addition, H. polymorpha has been highlighted as a promising recombinant protein expression host, especially due to the availability of strong and tightly regulatable promoters. In this study, we investigated the possibility of employing human serum albumin (HSA) as the fusion tag for the secretory expression of heterologous proteins in H. polymorpha. A set of four expression cassettes, which contained the methanol oxidase (MOX) promoter, translational HSA fusion tag, and the terminator of MOX, were constructed. The expression cassettes were also designed to contain sequences for accessory elements including His8-tag, linkers, tobacco etch virus protease recognition sites (Tev), multi-cloning sites, and strep-tags. To determine the effects of the size of the HSA fusion tag on the secretory expression of the target protein, each cassette contained the HSA gene fragment truncated at a specific position based on its domain structure. By using the Green fluorescence protein gene as the reporter, the properties of each expression cassette were compared in various conditions. Our results suggest that the translational HSA fusion tag is an efficient tool for the secretory expression of recombinant proteins in H. polymorpha.