Expression of heterologous proteins in Pichia pastoris: a useful experimental tool in protein engineering and production

Restriction site free cloning (RSFC) plasmid family for seamless, sequence independent cloning in Pichia pastoris

BACKGROUND

Tagging proteins is a standard method facilitating protein detection, purification or targeting. When tagging a certain protein of interest, it is challenging to predict which tag will give optimal results and will not interfere with protein folding, activity or yields. Ideally, multiple tags and positions are tested which however complicates molecular cloning and expression vector generation. In conventional cloning, tags are either added on PCR primers (requiring a distinct primer and PCR product per tag) or provided on the vector (typically leaving a restriction site scar).

RESULTS

Here we report a vector family of 40 plasmids allowing simple, seamless fusions of a single PCR product with various N- and C-terminal tags, signal sequences and promoters. The restriction site free cloning (RSFC) strategy presented in this paper relies on seamless cloning using type IIS restriction endonucleases. After cutting out a stuffer (placeholder) fragment from the vectors, a single PCR product can be directly inserted in frame into all 40 plasmids using blunt end or TA ligations, requiring only verification of the orientation. We have established a RSFC vector family for the commonly used protein expression host Pichia pastoris and demonstrated the system with the secretory expression of horseradish peroxidase (HRP). HRP fusions to four tags (Myc, FLAG, His, Strep) and two fusion proteins (GFP and MBP) showed a 31-fold difference in volumetric activities. C-terminal tagging caused in some cases almost a complete loss of function, whereas N-terminal tags showed moderate differences.

CONCLUSIONS

The RSFC vectors provide an unprecedented toolbox for expression optimization in P. pastoris. The results obtained with HRP underline the importance of comparing different tags to maximize activities of fusion proteins. In a similar fashion the RSFC strategy can be applied in other expression hosts to screen for optimal promoters, signal sequences or to facilitate the evaluation of (iso-) enzyme families.

Characterization of a novel manganese dependent endoglucanase belongs in GH family 5 from Phanerochaete chrysosporium

The cDNA encoding a putative glycoside hydrolase family 5, which has been predicted to be an endoglucanase (PcEg5A), was cloned from Phanerochaete chrysosporium and expressed in Pichia pastoris. PcEg5A contains a carbohydrate-binding domain and two important amino acids, E209 and E319, playing as proton donor and nucleophile in substrate catalytic domain. SDS-PAGE analysis indicated that the recombinant endoglucanase 5A (rPcEg5A) has a molecular size of 43 kDa which corresponds with the theoretical calculation. Optimum pH and temperature were found to be 4.5-6.0, and 50°C-60°C, respectively. Moreover, rPcEg5A exhibited maximal activity in the pH range of 3.0-8.0, whereas over 50% of activity still remained at 20°C and 80°C. rPcEg5A was stable at 60°C for 12 h incubation, indicating that rPcEg5A is a thermostable enzyme. Manganese ion enhanced the enzyme activity by 77%, indicating that rPcEg5A is a metal dependent enzyme. The addition of rPcEg5A to cellobiase (cellobiohydrolase and β-glucosidase) resulted in a 53% increasing saccharification of NaOH-pretreated barley straw, whereas the glucose release was 47% higher than that cellobiase treatment alone. Our study suggested that rPcEg5A is an enzyme with great potential for biomass saccharification.

Development of an IP-Free Biotechnology Platform for Constitutive Production of HPV16 L1 Capsid Protein Using the Pichia pastoris PGK1 Promoter

The human papillomavirus (HPV) L1 major capsid protein, which forms the basis of the currently available vaccines against cervical cancer, self-assembles into virus-like particles (VLPs) when expressed heterologously. We report the development of a biotechnology platform for HPV16 L1 protein expression based on the constitutive PGK1 promoter (P_PGK1) from the methylotrophic yeast Pichia pastoris. The L1 gene was cloned under regulation of P_PGK1 into pPGKΔ3 expression vector to achieve intracellular expression. In parallel, secretion of the L1 protein was obtained through the use of an alternative vector called pPGKΔ3α, in which a codon optimized α-factor signal sequence was inserted. We devised a work-flow based on the detection of the L1 protein by dot blot, colony blot, and western blot to classify the positive clones. Finally, intracellular HPV VLPs assembly was demonstrated for the first time in yeast cells. This study opens up perspectives for the establishment of an innovative platform for the production of HPV VLPs or other viral antigens for vaccination purposes, based on constitutive expression in P. pastoris.

High-level extracellular expression of inulin fructotransferase in Pichia pastoris for DFA III production

BACKGROUND

Inulin fructotransferase (IFTase) catalyzes inulin conversion to difructose anhydride (DFA III), which is a natural low-calorie sweetener. Although heterologous expression of IFTase was achieved in Escherichia coli, the extracellular enzyme activity was very low, which limited the commercialization of IFTase.

RESULTS

Active IFTase of about 43 kDa molecular mass of subunit was extracellularly expressed by Pichia pastoris and was greatly regulated by the IFTase gene copy number integrated into the P. pastoris genome and by the methanol concentration in the induction phase. Under optimized culture conditions, multicopy P. pastoris exhibited a maximum extracellular IFTase activity of 105.4 U mL(-1) in a 5 L fermenter, which was 8.9-fold the activity in shake flasks and 5.3-fold that obtained from wild-type strain.

CONCLUSION

IFTase was expressed in a eukaryotic P. pastoris system for the first time and achieved high-level extracellular expression using a high-cell-density fed-batch cultivation strategy. This demonstrated that P. pastoris was a good candidate for potential DFA III production as a novel IFTase expression system.

Cloning and Expression of Iranian Turkmen-thoroughbred Horse Follicle Stimulating Hormone in Pichia pastoris

BACKGROUND

Follicle stimulating hormone (FSH) plays an essential role in reproductive physiology and follicular development.

OBJECTIVE

A new variant of the equine fsh (efsh) gene was cloned, sequenced, and expressed in Pichia pastoris (P. pastoris) GS115 yeast expression system.

MATERIALS AND METHODS

The full-length cDNAs of the efshα and efshβ chains were amplified by reverse transcription polymerase chain reaction (RT-PCR) using the total RNA isolated from an Iranian Turkmen-thoroughbred horse's anterior pituitary gland. The amplified efsh chains were cloned into the pPIC9 vector and transferred into P. pastoris. The secretion of recombined eFSH using P. pastoris expression system was confirmed by Western blotting and immunoprecipitation (IP) methods.

RESULTS

The DNA sequence of the efshβ chain accession number JX861871, predicted two putative differential nucleotide arrays, both of which are located in the 3'UTR. Western blotting showed a molecular mass of 13 and 18 kDa for eFSHα and eFSHβ subunits, respectively. The expression of desired protein was confirmed by protein G immunoprecipitation kit.

CONCLUSIONS

eFSH successfully expressed in P. pastoris. These findings lay a foundation to improve ovulation and embryo recovery rates as well as the efficiency of total embryo-transfer process in mares.

Extracellular expression of alkaline phytase in Pichia pastoris: Influence of signal peptides, promoters and growth medium

Alkaline phytase isolated from pollen grains of Lilium longiflorum (LlALP) possesses unique catalytic and thermal stability properties that suggest it has the potential to be used as a feed supplement. However, substantial amounts of active enzymes are needed for animal feed studies and endogenous levels of LlALP in lily pollen are too low to provide the required amounts. Active rLlALP2 (coded by LlAlp2, one of two isoforms of alkaline phytase cDNA identified in lily pollen) has been successfully expressed in intracellular compartments of Pichia pastoris, however enzyme yields have been modest (25–30 mg/L) and purification of the enzyme has been challenging. Expression of foreign proteins to the extracellular medium of P. pastoris greatly simplifies protein purification because low levels of endogenous proteins are secreted by the yeast. In this paper, we first describe the generation of P. pastoris strains that will secrete rLlALP2 to the extracellular medium. Data presented here indicates that deletion of native signal peptides at the N- and C-termini of rLlALP2 enhanced α-mating factor (α-MF)-driven secretion by four-fold; chicken egg white lysozyme signal peptide was ineffective in the extracellular secretion of rLlALP2. Second, we describe our efforts to increase expression levels by employing a constitutive promoter from the glyceraldehyde-3-phosphate dehydrogenase gene (P_GAP) in place of the strong, tightly controlled promoter of alcohol oxidase 1 gene (P_AOX1). P_GAP enhanced the extracellular expression levels of rLlALP2 compared to P_AOX1. Finally, we report on the optimization of the culture medium to enhance yields of rLlALP2. The strength of P_GAP varies depending on the carbon source available for cell growth; secreted expression of rLlALP2 was highest when glycerol was the carbon source. The addition of histidine and Triton X-100 also enhanced extracellular expression. Taken together, the employment of P_GAP under optimized culture conditions resulted in approximately eight-fold (75–80 mg/L) increase in extracellular activity compared to P_AOXI (8–10 mg/L). The P. pastoris expression system can be employed as a source of active alkaline phytase for animal feed studies.

Role of N-linked glycosylation in the secretion and enzymatic properties of Rhizopus chinensis lipase expressed in Pichia pastoris

Background

The methylotrophic yeast, Pichia pastoris, is widely used as a useful experimental tool in protein engineering and production. It is common for proteins expressed in P. pastoris to exhibit N-glycosylation. In recent years, glycosylation studies in P. pastoris have attracted increasing attention from scholars. Rhizopus chinensis lipase (RCL) is one of the most important industrial lipases, and it has four potential N-linked glycosylation sites. The aim of the present study was to determine whether RCL undergoes asparagine-linked (N-linked) glycosylation and to examine the role of this modification in RCL expression and function.

Results

In this study, we demonstrated that RCL expressed in Pichia pastoris was N-glycosylated at the sites N-14, N-48 and N-60. The majority of the sites N-14 and N-60 were glycosylated, but the glycosylation degree of the site N-48 was only a very small portion. The glycan on N-60 played a key role in the expression and secretion of RCL. RT-PCR results showed that the mRNA level of proRCLCN60Q remained unchanged even though the protein secretion was hampered. Although the N-glycan on N-14 had no effect on the secretion of RCL, this glycan was beneficial for the lipase catalytic activity. On the other hand, the little amount of N-glycan on N-48 had no effect both on the secretion and activity of RCL in P. pastoris. Moreover, the thermostability analysis of RCL revealed that the lipase with more N-glycan was more thermostable.

Conclusions

RCL was N-glycosylated when expressed in P. pastoris. The N-glycans of RCL on the different sites had different functions for the secretion and enzymatic properties of the lipase. Our report may also provide theoretical support for the improvement of enzyme expression and stability based on the N-linked glycosylation modification to meet the future needs of the biotechnological industry.

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

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

A novel non-blue laccase from Bacillus amyloliquefaciens: secretory expression and characterization

Laccases are copper-containing enzymes which possess a promising potential in many industrial and environmental applications. Here we describe the cloning, extracellular expression and characterization of a novel non-blue laccase from Bacillus amyloliquefaciens in Pichia pastoris. The recombinant enzyme was secreted into the culture supernatant with high activity. It lacks the absorption band at 610 nm typical for blue laccases. However, electron paramagnetic resonance (EPR) spectrum proved the existence of type 1 copper center that was not detectable in the UV-visible spectrum. Metal content analysis revealed that the enzyme contains two copper ions, one iron ion and one zinc ion per protein molecular, suggesting that it is a novel non-blue laccase. The pH and temperature optima of the recombinant laccase were 6.6 and 60°C, respectively, and it was stable at pH 9.0 for 10 days. The enzyme activity was slightly activated by NaCl with concentration up to 200 mM. The purified laccase showed high efficiency in decolorizing reactive black 5 and indigo carmine, achieving more than 93% decolorization after 1h. The extreme robustness of the recombinant B. amyloliquefaciens laccase offers several advantages over most fungal laccases in various industrial applications.

Lentiviral Vectors Mediate Long-Term and High Efficiency Transgene Expression in HEK 293T cells

OBJECTIVES

Lentiviral vectors have been used successfully to rapidly produce decigram quantities of active recombinant proteins in mammalian cell lines. To optimize the protein production platform, the roles of Ubiquitous Chromatin Opening Element (UCOE), an insulator, and selected promoters were evaluated based on efficiency and stability of foreign gene expression mediated by lentiviral vectors.

METHODS

Five lentiviral vectors, pFIN-EF1α-GFP-2A-mCherH-WPRE containing EF1α promoter and HS4 insulator, p'HR.cppt.3'1.2kb-UCOE-SFFV-eGFP containing SFFV promoter and UCOE, pTYF-CMV(β-globin intron)-eGFP containing CMV promoter and β-globin intron, pTYF-CMV-eGFP containing CMV promoter, and pTYF-EF1α-eGFP with EF1α promoter were packaged, titered, and then transduced into 293T cells (1000 viral genomes per cell). The transduced cells were passaged once every three days at a ratio of 1:10. Expression level and stability of the foreign gene, green fluorescence protein (GFP), was evaluated using fluorescent microscopy and flow cytometry. Furthermore, we constructed a hepatitis C virus (HCV) E1 recombinant lentiviral vector, pLV-CMV-E1, driven by the CMV promoter. This vector was packaged and transduced into 293T cells, and the recombinant cell lines with stable expression of E1 protein were established by limiting dilution.

RESULTS

GFP expression in 293T cells transduced with the five lentiviral vectors peaked between passages 3 and 5 and persisted for more than 5 weeks. The expression was prolonged in the cells transduced with TYF-CMV (β-globin intron)-eGFP or TYF-CMV-eGFP, demonstrating less than a 50% decrease even at 9 weeks post transduction (p>0.05). The TYF-CMV-eGFP-transduced cells began with a higher level of GFP expression than other vectors did. The percentage of GFP positive cells for any of the five lentiviral vectors sustained over time. Moreover, the survival rates of all transfected cells exceeded 80% at both 5 and 9 weeks post transduction. Surprisingly, neither the HS4 insulator nor the UCOE sequence improved the GFP expression level or stability. Clonal cell lines with HCV E1 gene were generated from LV-CMV-E1 vector-infected 293T cells. A representative recombinant cell line maintained stable E1expression for at least 9 weeks without significant difference in morphology compared with untreated 293T cells.

CONCLUSION

The results suggest that all five vectors can stably transduce 293T cells, producing long term transgene expression with different efficiencies. However, neither the insulator nor the UCOE improved the GFP expression. The vectors containing the promoter CMV or CMV (β-globin intron) generated the highest gene expressions, manifesting as more favorable candidates for recombinant protein production in HEK293T cells.

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.

Efficient secretion of inulin fructotransferase in Pichia pastoris using the formaldehyde dehydrogenase 1 promoter

Inulin fructotransferase (IFTase) has received considerable attention due to its ability to catalyse inulin hydrolysis to difructose anhydride (DFA III), a natural low-calorie functional sweetener. In the present study, for the first time, we describe the expression of IFTase in Pichia pastoris under the control of the formaldehyde dehydrogenase 1 promoter (PFLD1). Using this system, we achieved efficient secretion with four substrate fed-batch strategies in a 3-L fermenter. The co-feeding induction strategy with methylamine hydrochloride and methanol achieved the maximum extracellular IFTase activity of 62.72 U mL−1, which was 3.2-fold higher than that obtained with the wild-type strain. In addition to methanol, carbon sources such as glucose and glycerol could also be utilised by PFLD1-controlled P. pastoris for IFTase production using methylamine hydrochloride induction. However, we found that glycerol and glucose should be strictly controlled at low concentrations of 0.5–1.5 % (v/v) and 1–1.5 % (w/v), respectively. The use of glycerol and glucose demonstrated that P. pastoris was also attractive for IFTase production via methanol-free cultivation strategies. This study may provide the basis for the industrial use of this recombinant IFTase for the production of DFA III.

High-level expression and characterization of a thermostable xylanase mutant from Trichoderma reesei in Pichia pastoris

A gene encoding xylanase 2 mutant from Trichoderma reesei (T2C/T28C, named mxyn2) was cloned into the Pichia pastoris X33 strain using the vector pPICZαA. Recombinant Mxyn2p was functionally expressed in P. pastoris X33 and secreted into the supernatant. Real time qPCR demonstrated that an increase in gene copy number correlated with higher levels of expression. Supernatant from methanol induced cells was concentrated by ultrafiltration with a 10kDa cut off membrane, and purified with ion exchange chromatography using SP Sepharose Fast Flow chromatography. Recombinant Mxyn2p protein had the highest activity at 75°C, while recombinant protein encoded by the "wild type" xylanase gene xyn2, also expressed in Pichia, was 20°C lower. The Mxyn2p enzyme retained more than 70% of its activity after incubation at 80°C for 10min. The effects of the optimal pH and temperature for higher expression levels in P. pastoris were also determined, 6.0 and 22°C, respectively. The maximum xylanase activity of Mxyn2p was 13,000nkat/mg (9.88g/l) in fed-batch cultivation after 168h induction with methanol in a 50l bioreactor.

The pCri System: a vector collection for recombinant protein expression and purification

A major bottleneck in structural, biochemical and biophysical studies of proteins is the need for large amounts of pure homogenous material, which is generally obtained by recombinant overexpression. Here we introduce a vector collection, the pCri System, for cytoplasmic and periplasmic/extracellular expression of heterologous proteins that allows the simultaneous assessment of prokaryotic and eukaryotic host cells (Escherichia coli, Bacillus subtilis, and Pichia pastoris). By using a single polymerase chain reaction product, genes of interest can be directionally cloned in all vectors within four different rare restriction sites at the 5'end and multiple cloning sites at the 3'end. In this way, a number of different fusion tags but also signal peptides can be incorporated at the N- and C-terminus of proteins, facilitating their expression, solubility and subsequent detection and purification. Fusion tags can be efficiently removed by treatment with site-specific peptidases, such as tobacco etch virus proteinase, thrombin, or sentrin specific peptidase 1, which leave only a few extra residues at the N-terminus of the protein. The combination of different expression systems in concert with the cloning approach in vectors that can fuse various tags makes the pCri System a valuable tool for high throughput studies.

The shapes of Z-α1-antitrypsin polymers in solution support the C-terminal domain-swap mechanism of polymerization

Emphysema and liver cirrhosis can be caused by the Z mutation (Glu342Lys) in the serine protease inhibitor α1-antitrypsin (α1AT), which is found in more than 4% of the Northern European population. Homozygotes experience deficiency in the lung concomitantly with a massive accumulation of polymers within hepatocytes, causing their destruction. Recently, it was proposed that Z-α1AT polymerizes by a C-terminal domain swap. In this study, small-angle x-ray scattering (SAXS) was used to characterize Z-α1AT polymers in solution. The data show that the Z-α1AT trimer, tetramer, and pentamer all form ring-like structures in strong support of a common domain-swap polymerization mechanism that can lead to self-terminating polymers.

Enhanced expression of recombinant elastase in Pichia pastoris through the substitution of Thr for Ser in Asn-Xaa-Ser sequons

N-glycosylation usually occurs at the Asn-Xaa-Ser/Thr sequon of glycoproteins in Pichia pastoris, exerting great effects on expression efficiency; however, Asn-Xaa-Thr is more efficiently glycosylated than Asn-Xaa-Ser. In this study, the role of the two sequons in the expression of recombinant elastase (rPAE) was investigated. At N43, N212, and N280 of rPAE, Asn-Xaa-Thr was substituted for the native Asn-Xaa-Ser sequon through site-directed mutagenesis, and the two sequon forms were introduced into rPAE at N36 and N264. As expected, substitution at N36, N43, N212, and N280 enhanced the degree of N-glycosylation. At N212 or N280, substitution increased rPAE production effectively by 43 and 25 %, respectively. In comparison, at N36, N43, and N264, the change inhibited rPAE expression to varying extents; specifically, substitution at N36 resulted in a 31 % decrease, while substitution at N43 or N264 resulted in a decrease of less than 9 %. It is suggested that the effect of the substitution of Asn-Xaa-Thr for Asn-Xaa-Ser on rPAE expression is roughly related to the role of the original Asn-Xaa-Ser sequon. As the conversion of Ser to Thr at N-glycosylation sites through site-directed mutagenesis is easily achieved, it is a feasible means of improving the expression of recombinant proteins in P. pastoris.

Characterization of the antigenicity of Cpl1, a surface protein of Cryptococcus neoformans var. neoformans

Cryptococcus neoformans var. neoformans is an important fungal pathogen. The capsule is a well established virulence factor and a target site for diagnostic tests. The CPL1 gene is required for capsular formation and virulence. The protein product Cpl1 has been proposed to be a secreted protein, but the characteristics of this protein have not been reported. Here we sought to characterize Cpl1. Phylogenetic analysis showed that the Cpl1 of C. neoformans var. neoformans and the Cpl1 orthologs identified in C. neoformans var. grubii and C. gattii formed a distinct cluster among related fungi; while the putative ortholog found in Trichosporon asahii was distantly related to the Cryptococcus cluster. We expressed Cpl1 abundantly as a secreted His-tagged protein in Pichia pastoris. The protein was used to immunize guinea pigs and rabbits for high titer mono-specific polyclonal antibody that was shown to be highly specific against the cell wall of C. neoformans var. neoformans and did not cross react with C. gattii, T. asahii, Aspergillus spp., Candida spp. and Penicillium spp. Using the anti-Cpl1 antibody, we detected Cpl1 protein in the fresh culture supernatant of C. neoformans var. neoformans and we showed by immunostaining that the Cpl1 protein was located on the surface. The Cpl1 protein is a specific surface protein of C. neoformans var. neoformans.

High efficient expression of a functional humanized single-chain variable fragment (scFv) antibody against CD22 in Pichia pastoris

Single-chain variable fragments (scFvs) have recently emerged as attractive candidates in targeted immunotherapy of various malignancies. The anti-CD22 scFv is able to target CD22, on B cell surface and is being considered as a promising molecule in targeted immunotherapy of B cell malignancies. The recombinant anti-CD22 scFv has been successfully expressed in Escherichia coli; however, the insufficient production yield has been a major bottleneck for its therapeutic application. The methylotrophic yeast Pichia pastoris has become a highly popular expression host for the production of a wide variety of recombinant proteins such as antibody fragments. In this study, we used the Pichia expression system to express a humanized scFv antibody against CD22. The full-length humanized scFv gene was codon optimized, cloned into the pPICZαA and expressed in GS115 strain. The maximum production level of the scFv (25 mg/L) were achieved at methanol concentration, 1 %; pH 6.0; inoculum density, OD600 = 3 and the induction time of 72 h. The correlation between scFv gene dosage and expression level was also investigated by real-time PCR, and the results confirmed the presence of such correlation up to five gene copies. Immunofluorescence and flow cytometry studies and Biacore analysis demonstrated binding to CD22 on the surface of human lymphoid cell line Raji and recombinant soluble CD22, respectively. Taken together, the presented data suggest that the Pichia pastoris can be considered as an efficient host for the large-scale production of anti-CD22 scFv as a promising carrier for targeted drug delivery in treatment of CD22(+) B cell malignancies.

The recombinant expression systems for structure determination of eukaryotic membrane proteins

Eukaryotic membrane proteins, many of which are key players in various biological processes, constitute more than half of the drug targets and represent important candidates for structural studies. In contrast to their physiological significance, only very limited number of eukaryotic membrane protein structures have been obtained due to the technical challenges in the generation of recombinant proteins. In this review, we examine the major recombinant expression systems for eukaryotic membrane proteins and compare their relative advantages and disadvantages. We also attempted to summarize the recent technical strategies in the advancement of eukaryotic membrane protein purification and crystallization.

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

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

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.

Antibacterial Activity of Recombinant Pig Intestinal Parasite Cecropin P4 Peptide Secreted from Pichia pastoris

Cecropins (Cec) are antibacterial peptides and their expression is induced in a pig intestinal parasite Ascaris suum by bacterial infection. To explore the usefulness of its activity as an antibiotic, CecP4 cDNA was prepared and cloned into the pPICZ B expression vector and followed by the integration into AOX1 locus in Pichia pastoris. The supernatants from cell culture were collected after methanol induction and concentrated for the test of antimicrobial activity. The recombinant P. patoris having CecP4 showed antimicrobial activity when tested against Staphyllococcus aureus in disc diffusion assay. We selected one of the CecP4 clones (CecP4-2) and performed further studies with it. The growth of recombinant P. pastoris was optimized using various concentration of methanol, and it was found that 2% methanol in the culture induced more antibacterial activity, compared to 1% methanol. We extended the test of antimicrobial activity by applying the concentrated supernatant of CecP4 culture to Pseudomonas aeruginosa and E. coli respectively. Recombinant CecP4 also showed antimicrobial activity against both Pseudomona and E. coli, suggesting the broad spectrum of its antimicrobial activity. After improvements for the scale-up, it will be feasible to use recombinant CecP4 for supplementation to the feed to control microbial infections in young animals, such as piglets.

Enhanced expression of recombinant elastase in Pichia pastoris through addition of N-glycosylation sites to the propeptide

N-Glycosylation is a common form of protein post-translational modification in Pichia pastoris and greatly affects folding and secretion. The propeptide of the Pseudomonas aeruginosa elastase (PAE) is indispensable for proper folding and secretion of the enzyme. We have studied the effect of introducing N-glycosylation sites to the propeptide of the recombinant elastase (rPAE) on its expression levels in P. pastoris. Addition of N-glycosylation sites to the propeptide at N51 or N93 enhanced rPAE production levels by 104 or 57%, respectively, while addition at N11 or N127 led to a 25 or 50% decrease, respectively. The introduced N-glycosylation sites in the propeptide at these four sites exerted a null effect on the N-glycosylation degree of mature rPAE.

Recombinant antigens expressed in Pichia pastoris for the diagnosis of sleeping sickness caused by Trypanosoma brucei gambiense

BACKGROUND

Screening tests for gambiense sleeping sickness, such as the CATT/T. b. gambiense and a recently developed lateral flow tests, are hitherto based on native variant surface glycoproteins (VSGs), namely LiTat 1.3 and LiTat 1.5, purified from highly virulent trypanosome strains grown in rodents.

METHODOLOGY/PRINCIPAL FINDINGS

We have expressed SUMO (small ubiquitin-like modifier) fusion proteins of the immunogenic N-terminal part of these antigens in the yeast Pichia pastoris. The secreted recombinant proteins were affinity purified with yields up to 10 mg per liter cell culture.

CONCLUSIONS/SIGNIFICANCE

The diagnostic potential of each separate antigen and a mixture of both antigens was confirmed in ELISA on sera from 88 HAT patients and 74 endemic non-HAT controls. Replacement of native antigens in the screening tests for sleeping sickness by recombinant proteins will eliminate both the infection risk for the laboratory staff during antigen production and the need for laboratory animals. Upscaling production of recombinant antigens, e.g. in biofermentors, is straightforward thus leading to improved standardisation of antigen production and reduced production costs, which on their turn will increase the availability and affordability of the diagnostic tests needed for the elimination of gambiense HAT.

Heterologous expression and characterization of laccase 2 from Coprinopsis cinerea capable of decolourizing different recalcitrant dyes

The gene (CcLcc2) encoding laccase from the basidiomycete Coprinopsis cinerea Okayama-7 #130 was synthesized by polymerase chain reaction-based two-step DNA synthesis, and heterologously expressed in Pichia pastoris. The recombinant protein was purified by ammonium sulphate precipitation and nickel nitrilotriacetic acid chromatography. The molecular mass of CcLcc2 was estimated to be 54 kDa by denaturing polyacrylamide gel electrophoresis. The optimum pH and temperature for laccase catalysis for the oxidation of 2,2ʹ-azino-bis(3-ethylbenzothiazoline-6-sulphonate) (ABTS) were 2.6 and 45 °C, respectively. The Km values of the enzyme towards the substrates ABTS, 2,6-dimethoxyphenol (2,6-DMP) and guaiacol were 0.93, 1.02 and 28.07 mmol·L⁻¹, respectively. The decolourization of methyl orange, crystal violet and malachite green, commonly used in the textile industry, was assessed. The decolourization percentage of crystal violet and malachite green was 80% after 4 h of reaction, and that of methyl orange was 50% at 4 h. These results show that the CcLcc2 has enormous potential for the decolourization of highly stable triphenylmethane dyes.

Optimising expression of the recombinant fusion protein biopesticide ω-hexatoxin-Hv1a/GNA in Pichia pastoris: sequence modifications and a simple method for the generation of multi-copy strains

Production of recombinant protein bio-insecticides on a commercial scale can only be cost effective if host strains with very high expression levels are available. A recombinant fusion protein containing an arthropod toxin, ω-hexatoxin-Hv1a, (from funnel web spider Hadronyche versuta) linked to snowdrop lectin (Galanthus nivalis agglutinin; GNA) is an effective oral insecticide and candidate biopesticide. However, the fusion protein was vulnerable to proteolysis during production in the yeast Pichia pastoris. To prevent proteolysis, the Hv1a/GNA fusion expression construct was modified by site-directed mutagenesis to remove a potential Kex2 cleavage site at the C-terminus of the Hv1a peptide. To obtain a high expressing clone of P. pastoris to produce recombinant Hv1a/GNA, a straightforward method was used to produce multi-copy expression plasmids, which does not require multiple integrations to give clones of P. pastoris containing high copy numbers of the introduced gene. Removal of the Kex2 site resulted in increased levels of intact fusion protein expressed in wild-type P. pastoris strains, improving levels of intact recombinant protein recoverable. Incorporation of a C-terminal (His)6 tag enabled single step purification of the fusion protein. These modifications did not affect the insecticidal activity of the recombinant toxin towards lepidopteran larvae. Introduction of multiple expression cassettes increased the amount of secreted recombinant fusion protein in a laboratory scale fermentation by almost tenfold on a per litre of culture basis. Simple modifications in the expression construct can be advantageous for the generation of high expressing P. pastoris strains for production of a recombinant protein, without altering its functional properties.

Expression of endoglucanases in Pichia pastoris under control of the GAP promoter

Background

Plant-derived biomass is a potential alternative to fossil feedstocks for a greener economy. Enzymatic saccharification of biomass has been studied extensively and endoglucanases have been found to be a prerequisite for quick initial liquefaction of biomass under industrial conditions. Pichia pastoris, widely used for heterologous protein expression, can be utilized for fungal endoglucanase production. The recently marketed PichiaPink™ expression system allows for rapid clone selection, and employs the methanol inducible AOX1 promoter to ensure high protein expression levels. However, methanol is toxic and poses a fire hazard, issues which become more significant at an industrial scale. It is possible to eliminate these risks and still maintain high productivity by switching to the constitutive GAP promoter.

Results

In the present study, a plasmid carrying the constitutive GAP promoter was created for PichiaPink™. We then studied expression of two endoglucanases, AfCel12A from Aspergillus fumigatus and TaCel5A from Thermoascus aurantiacus, regulated by either the AOX1 promoter or the GAP promoter. Initial experiments in tubes and small bioreactors showed that the levels of AfCel12A obtained with the constitutive promoter were similar or higher, compared to the AOX1 promoter, whereas the levels of TaCel5A were somewhat lower. After optimization of cultivation conditions using a 15-l bioreactor, the recombinant P. pastoris strains utilizing the GAP promoter produced ca. 3–5 g/l of total secreted protein, with CMCase activity equivalent to 1200 nkat/ml AfCel12A and 170 nkat/ml TaCel5A.

Conclusions

We present a strategy for constitutive recombinant protein expression in the novel PichiaPink™ system. Both AfCel12A and TaCel5A were successfully expressed constitutively in P. pastoris under the GAP promoter. Reasonable protein levels were reached after optimizing cultivation conditions.