Increasing gene dosage greatly enhances recombinant expression of aquaporins in Pichia pastoris

Brassica oleracea L. var. italica Aquaporin Reconstituted Proteoliposomes as Nanosystems for Resveratrol Encapsulation

Aquaporins (AQPs), membrane proteins responsible for facilitating water transport, found in plant membrane vesicles (MV), have been related to the functionality and stability of MV. We focused on AQPs obtained from broccoli, as they show potential for biotechnological applications. To gain further insight into the role of AQPs in MV, we describe the heterologous overexpression of two broccoli AQPs (BoPIP1;2 and BoPIP2;2) in Pichia pastoris, resulting in their purification with high yield (0.14 and 0.99 mg per gram cells for BoPIP1;2 and BoPIP2;2). We reconstituted AQPs in liposomes to study their functionality, and the size of proteoliposomes did not change concerning liposomes. BoPIP2;2 facilitated water transport, which was preserved for seven days at 4 °C and at room temperature but not at 37 °C. BoPIP2;2 was incorporated into liposomes to encapsulate a resveratrol extract, resulting in increased entrapment efficiency (EE) compared to conventional liposomes. Molecular docking was utilized to identify binding sites in PIP2s for resveratrol, highlighting the role of aquaporins in the improved EE. Moreover, interactions between plant AQP and human integrin were shown, which may increase internalization by the human target cells. Our results suggest AQP-based alternative encapsulation systems can be used in specifically targeted biotechnological applications.

A switchable secrete-and-capture system enables efficient selection of Pichia pastoris clones producing high yields of Fab fragments

Pichia pastoris (syn. Komagataella phaffii) represents a commonly used expression system in the biotech industry. High clonal variation of transformants, however, typically results in a broad range of specific productivities for secreted proteins. To isolate rare clones with exceedingly high product titers, an extensive number of clones need to be screened. In contrast to high-throughput screenings of P. pastoris clones in microtiter plates, secrete-and-capture methodologies have the potential to efficiently isolate high-producer clones among millions of cells through fluorescence-activated cell sorting (FACS). Here, we describe a novel approach for the non-covalent binding of fragment antigen-binding (Fab) proteins to the cell surface for the isolation of high-producing clones. Eight different single-chain variable fragment (scFv)-based capture matrices specific for the constant part of the Fabs were fused to the Saccharomyces cerevisiae alpha-agglutinin (SAG1) anchor protein for surface display in P. pastoris. By encoding the capture matrix on an episomal plasmid harboring inherently unstable autonomously replicating sequences (ARS), this secrete-and-capture system offers a switchable scFv display. Efficient plasmid clearance upon removal of selective pressure enabled the direct use of isolated clones for subsequent Fab production. Flow-sorted clones (n = 276) displaying high amounts of Fabs showed a significant increase in median Fab titers detected in the cell-free supernatant (CFS) compared to unsorted clones (n = 276) when cells were cultivated in microtiter plates (factor in the range of ∼21-49). Fab titers of clones exhibiting the highest product titer observed for each of the two approaches were increased by up to 8-fold for the sorted clone. Improved Fab yields of sorted cells vs. unsorted cells were confirmed in an upscaled shake flask cultivation of selected candidates (factor in the range of ∼2-3). Hence, the developed display-based selection method proved to be a valuable tool for efficient clone screening in the early stages of our bioprocess development.

Characterization of the Aquaporin-9 Inhibitor RG100204 In Vitro and in db/db Mice

Aquaporin-9 (AQP9) is a facilitator of glycerol and other small neutral solute transmembrane diffusion. Identification of specific inhibitors for aquaporin family proteins has been difficult, due to high sequence similarity between the 13 human isoforms, and due to the limited channel surface areas that permit inhibitor binding. The few AQP9 inhibitor molecules described to date were not suitable for in vivo experiments. We now describe the characterization of a new small molecule AQP9 inhibitor, RG100204 in cell-based calcein-quenching assays, and by stopped-flow light-scattering recordings of AQP9 permeability in proteoliposomes. Moreover, we investigated the effects of RG100204 on glycerol metabolism in mice. In cell-based assays, RG100204 blocked AQP9 water permeability and glycerol permeability with similar, high potency (~5 × 10-8 M). AQP9 channel blocking by RG100204 was confirmed in proteoliposomes. After oral gavage of db/db mice with RG100204, a dose-dependent elevation of plasma glycerol was observed. A blood glucose-lowering effect was not statistically significant. These experiments establish RG100204 as a direct blocker of the AQP9 channel, and suggest its use as an experimental tool for in vivo experiments on AQP9 function.

Effect of N-glycosylation on secretion, stability, and biological activity of recombinant human interleukin-3 (hIL-3) in Pichia pastoris

Human interleukin-3 (hIL-3) is a clinically important cytokine used to treat hematological malignancies, bone marrow transplantation, cytopenias, and immunological disorders. The cloning of hIL-3 gene was previously reported by our group, where its expression was optimized under methanol-inducible AOX1 promoter having N-terminal α mating factor signal sequence from Saccharomyces cerevisiae. This study investigated the role of glycosylation pattern on its molecular stability, secretion efficiency, and biological activity using the mutagenesis approach. The two N-linked glycosylation positions at N15th (Asn15) and N70th (Asn70) were sequentially mutated to generate three recombinant hIL-3 variants, i.e., N15A, N70A, and N15/70A. Asparagine at these positions was replaced with non-polar alanine amino acid (Ala, A). The alteration of N-linked glycosylation sites was disadvantageous to its efficient secretion in Pichia pastoris, where a 52.32%, 36.48%, 71.41% lower production was observed in N15A, N70A, and N15/70A mutants, respectively, as compared to native control. The fully glycosylated native hIL-3 protein showed higher thermal stability over its deglycosylated counterparts. The biological activity of native, N15A, N70A, and N15/70A hIL-3 protein was evaluated, where N15/70A mutant showed slightly higher proliferation efficacy than other combinations.

Potential of the Signal Peptide Derived from the PAS_chr3_0030 Gene Product for Secretory Expression of Valuable Enzymes in Pichia pastoris

Pichia pastoris is widely used for the production of valuable recombinant proteins. An advantage of P. pastoris over other expression systems is that it secretes low levels of endogenous proteins, which facilitates the purification processes if the desired recombinant proteins are efficiently secreted into the culture medium. However, not all recombinant proteins can be successfully secreted by P. pastoris, especially enzymes that are located in intracellular compartments in their native hosts. Few studies have reported strategies for releasing recombinant proteins which cannot be secreted by standard protocols. Here, we investigated whether this challenge can be addressed using novel secretion leaders. Analysis of the secretome and transcriptome of P. pastoris indicated that the four genes with the highest protein-to-transcript ratios were EPX1, PAS_chr3_0030, SCW10, and UTH1, suggesting that their gene products contain efficient secretion leaders. Our data revealed that the signal peptide derived from the PAS_chr3_0030 gene product conferred secretion competence to certain industrial enzymes, e.g., a nitrilase of Alcaligenes faecalis ZJUTB10, a ribosylnicotinamide kinase of P. pastoris, and a glucose dehydrogenase of Exiguobacterium sibiricum. Therefore, the signal peptide derived from the PAS_chr3_0030 gene product represents a novel secretion sequence for the secretory expression of recombinant enzymes in P. pastoris. IMPORTANCE Although P. pastoris is widely used for the secretory production of pharmaceutical proteins, its successful applications in the secretory production of industrial enzymes are limited. The α-mating factor pre-pro leader is the most widely used secretion signal in P. pastoris, but numerous industrial enzymes cannot be secreted using it. The importance of this study is that we identified a signal peptide derived from the PAS_chr3_0030 gene product which conferred secretion competence to three-quarters of the enzymes tested. This signal peptide derived from the PAS_chr3_0030 gene product may facilitate the application of P. pastoris in industrial biocatalysis.

Optimization of Pichia pastoris Expression System for High-Level Production of Margatoxin

Margatoxin (MgTx) is a high-affinity blocker of voltage-gated potassium (Kv) channels. It inhibits Kv1.1–Kv1.3 ion channels in picomolar concentrations. This toxin is widely used to study physiological function of Kv ion channels in various cell types, including immune cells. Isolation of native MgTx in large quantities from scorpion venom is not affordable. Chemical synthesis and recombinant production in Escherichia coli need in vitro oxidative refolding for proper disulfide bond formation, resulting in a very low yield of peptide production. The Pichia pastoris expression system offers an economical approach to overcome all these limitations and gives a higher yield of correctly refolded recombinant peptides. In this study, improved heterologous expression of recombinant MgTx (rMgTx) in P. pastoris was obtained by using preferential codons, selecting the hyper-resistant clone against Zeocin, and optimizing the culturing conditions. About 36 ± 4 mg/L of >98% pure His-tagged rMgTx (TrMgTx) was produced, which is a threefold higher yield than has been previously reported. Proteolytic digestion of TrMgTx with factor Xa generated untagged rMgTx (UrMgTx). Both TrMgTx and UrMgTx blocked the Kv1.2 and Kv1.3 currents (patch-clamp) (K_d for Kv1.2 were 64 and 14 pM, and for Kv1.3, 86 and 50 pM, respectively) with comparable potency to the native MgTx. The analysis of the binding kinetics showed that TrMgTx had a lower association rate than UrMgTx for both Kv1.2 and Kv1.3. The dissociation rate of both the analogues was the same for Kv1.3. However, in the case of Kv1.2, TrMgTx showed a much higher dissociation rate with full recovery of the block than UrMgTx. Moreover, in a biological functional assay, both peptides significantly downregulated the expression of early activation markers IL2R and CD40L in activated CD4⁺ T_EM lymphocytes whose activation was Kv1.3 dependent. In conclusion, the authors report that the Pichia expression system is a powerful method to produce disulfide-rich peptides, the overexpression of which could be enhanced noticeably through optimization strategies, making it more cost-effective. Since the presence of the His-tag on rMgTx only mildly altered the block equilibrium and binding kinetics, recombinant toxins could be used in ion channel research without removing the tag and could thus reduce the cost and time demand for toxin production.

Oxidative stress tolerance contributes to heterologous protein production in Pichia pastoris

BACKGROUND

Pichia pastoris (syn. Komagataella phaffii) is an important yeast system for heterologous protein expression. A robust P. pastoris mutant with oxidative and thermal stress cross-tolerance was acquired in our previous study. The robust mutant can express a 2.5-fold higher level of lipase than its wild type (WT) under methanol induction conditions.

RESULTS

In this study, we found that the robust mutant not only can express a high level of lipase, but also can express a high level of other heterogeneous proteins (e.g., green fluorescence protein) under methanol induction conditions. Additionally, the intracellular reactive oxygen species (ROS) levels in the robust mutant were lower than that in the WT under methanol induction conditions. To figure out the difference of cellular response to methanol between the WT and the robust mutant, RNA-seq was detected and compared. The results of RNA-seq showed that the expression levels of genes related to antioxidant, MAPK pathway, ergosterol synthesis pathway, transcription factors, and the peroxisome pathway were upregulated in the robust mutant compared to the WT. The upregulation of these key pathways can improve the oxidative stress tolerance of strains and efficiently eliminate cellular ROS. Hence, we inferred that the high heterologous protein expression efficiency in the robust mutant may be due to its enhanced oxidative stress tolerance. Promisingly, we have indeed increased the expression level of lipase up to 1.6-fold by overexpressing antioxidant genes in P. pastoris.

CONCLUSIONS

This study demonstrated the impact of methanol on the expression levels of genes in P. pastoris and emphasized the contribution of oxidative stress tolerance on heterologous protein expression in P. pastoris. Our results shed light on the understanding of protein expression mechanism in P. pastoris and provided an idea for the rational construction of robust yeast with high expression ability.

Enhanced Secretory Expression and Surface Display Level of Bombyx mori Acetylcholinesterase 2 by Pichia pastoris Based on Codon Optimization Strategy for Pesticides Setection

The cholinesterase-based spectrophotometric assay, also called enzyme inhibition method, is a good choice for rapid detection of organophosphate pesticides (OPs) and carbamate pesticides (CPs). Obviously, the cholinesterase is the core reagent in enzyme inhibition method. In our previous work, a recombinant acetylcholinesterase 2 from Bombyx mori (rBmAChE2) was expressed in yeast successfully and exhibited great sensitivity. However, the yield of rBmAChE2 is not desirable. In this study, a codon optimization strategy was employed to enhance the yield of rBmAChE2 in Pichia pastoris GS115. Results showed that by replacing 6 key rare codons and increasing the percentage of bases G and C up to 46.85%, codon adaptation index (CAI) of Bombyx mori acetylcholinesterase 2 (bmace2) gene was improved from 0.70 to 0.81. After being transformed into Pichia pastoris GS115 via electroporation, the expression transformant can produce 139.7 U/mL secretory codon-optimized rBmAChE2 (opt-rBmAChE2) in the culture supernatant, 3.62 times higher than that of strain bearing the wild-type bmace2 gene. Meanwhile, opt-rBmAChE2 displayed on the yeast surface was up to 2280.02 U/g, 2.8 times higher than wild-type displayed rBmAChE2. In addition, either secretory or surface-displayed opt-rBmAChE2 maintained the similar sensitivities to the wild-type rBmAChE2 for tested inhibitors. Furthermore, the detection limits of the opt-rBmAChE2-based enzyme inhibition method for 10 kinds of OPs or CPs (0.01-2.69 mg/kg) were lower than most of the indexes present in current standard method (GB/T 5009.199-2003) or the maximum residue limits (GB 2763-2019) in China. The results might contribute to the utilization of rBmAChE2 for pesticide residue screening detection in practice.

Established tools and emerging trends for the production of recombinant proteins and metabolites in Pichia pastoris

Besides bakers' yeast, the methylotrophic yeast Komagataella phaffii (also known as Pichia pastoris) has been developed into the most popular yeast cell factory for the production of heterologous proteins. Strong promoters, stable genetic constructs and a growing collection of freely available strains, tools and protocols have boosted this development equally as thorough genetic and cell biological characterization. This review provides an overview of state-of-the-art tools and techniques for working with P. pastoris, as well as guidelines for the production of recombinant proteins with a focus on small-scale production for biochemical studies and protein characterization. The growing applications of P. pastoris for in vivo biotransformation and metabolic pathway engineering for the production of bulk and specialty chemicals are highlighted as well.

Codon usage bias regulates gene expression and protein conformation in yeast expression system P. pastoris

Background

Protein synthesis is one of the extremely important anabolic pathways in the yeast expression system Pichia pastoris. Codon optimization is a commonly adopted strategy for improved protein expression, although unexpected failures did appear sometimes waiting for further exploration. Recently codon bias has been studied to regulate protein folding and activity in many other organisms.

Results

Here the codon bias profile of P. pastoris genome was examined first and a direct correlation between codon translation efficiency and usage frequency was identified. By manipulating the codon choices of both endogenous and heterologous signal peptides, secretion abilities of N-terminal signal peptides were shown to be tolerant towards codon changes. Then two gene candidates with different levels of structural disorder were studied, and full-length codon optimization was found to affect their expression profiles differentially. Finally, more evidences were provided to support possible protein conformation change brought by codon optimization in structurally disordered proteins.

Conclusion

Our results suggest that codon bias regulates gene expression by modulating several factors including transcription and translation efficiency, protein folding and activity. Because of sequences difference, the extent of affection may be gene specific. For some genes, special codon optimization strategy should be adopted to ensure appropriate expression and conformation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01580-9.

Expression and Purification of Human Mitochondrial Intramembrane Protease PARL

Rhomboid proteases are a ubiquitous superfamily of serine intramembrane peptidases that play a role in a wide variety of cellular processes. The mammalian mitochondrial rhomboid protease, Presenilin-Associated Rhomboid Like (PARL), is a critical regulator of mitochondrial homeostasis through the cleavage of its substrates, which have roles in mitochondrial quality control and apoptosis. However, neither structural nor functional information for this important protease is available, because the expression of eukaryotic membrane proteins to sufficient levels in an active form often represents a major bottleneck for in vitro studies. Here we present an optimized protocol for expression and purification of the human PARL protease using the eukaryotic expression host Pichia pastoris. The PARL gene construct was generated in tandem with green fluorescent protein (GFP), which allowed for the selection of high expressing clones and monitoring during the large-scale expression and purification steps. We discuss the production protocol with precise details for each step. The protocol yields 1 mg of pure PARL per liter of yeast culture.

Identification of a novel promoter for driving antibiotic-resistant genes to reduce the metabolic burden during protein expression and effectively select multiple integrations in Pichia Pastoris

Routine approaches for the efficient expression of heterogenous proteins in Pichia pastoris include using the strong methanol-regulated alcohol oxidase (AOX1) promoter and multiple inserts of expression cassettes. To screen the transformants harboring multiple integrations, antibiotic-resistant genes such as the Streptoalloteichus hindustanus bleomycin gene are constructed into expression vectors, given that higher numbers of insertions of antibiotic-resistant genes on the expression vector confer resistance to higher concentrations of the antibiotic for transformants. The antibiotic-resistant genes are normally driven by the strong constitutive translational elongation factor 1a promoter (P_TEF1). However, antibiotic-resistant proteins are necessary only for the selection process. Their production during the heterogenous protein expression process may increase the burden in cells, especially for the high-copy strains which harbor multiple copies of the expression cassette of antibiotic-resistant genes. Besides, a high concentration of the expensive antibiotic is required for the selection of multiple inserts because of the effective expression of the antibiotic-resistant gene by the TEF1 promoter. To address these limitations, we replaced the TEF1 promoter with a weaker promoter (P_Dog2p300) derived from the potential promoter region of 2-deoxyglucose-6-phosphate phosphatase gene for driving the antibiotic-resistant gene expression. Importantly, the P_Dog2p300 has even lower activity under carbon sources (glycerol and methanol) used for the AOX1 promoter-based production of recombinant proteins compared with glucose that is usually used for the selection process. This strategy has proven to be successful in screening of transformants harboring more than 3 copies of the gene of interest by using plates containing 100 μg/ml of Zeocin. Meanwhile, levels of Zeocin resistance protein were undetectable by immunoblotting in these multiple-copy strains during expression of heterogenous proteins.Key points• P_Dog2p300 was identified as a novel glucose-regulated promoter.• The expression of antibiotic-resistant gene driven by P_Dog2p300 was suppressed during the recombinant protein expression, resulting in reducing the metabolic burden.• The transformants harboring multiple integrations were cost-effectively selected by using the P_Dog2p300 for driving antibiotic-resistant genes.

Robust and flexible platform for directed evolution of yeast genetic switches

A wide repertoire of genetic switches has accelerated prokaryotic synthetic biology, while eukaryotic synthetic biology has lagged in the model organism Saccharomyces cerevisiae. Eukaryotic genetic switches are larger and more complex than prokaryotic ones, complicating the rational design and evolution of them. Here, we present a robust workflow for the creation and evolution of yeast genetic switches. The selector system was designed so that both ON- and OFF-state selection of genetic switches is completed solely by liquid handling, and it enabled parallel screen/selection of different motifs with different selection conditions. Because selection threshold of both ON- and OFF-state selection can be flexibly tuned, the desired selection conditions can be rapidly pinned down for individual directed evolution experiments without a prior knowledge either on the library population. The system's utility was demonstrated using 20 independent directed evolution experiments, yielding genetic switches with elevated inducer sensitivities, inverted switching behaviours, sensory functions, and improved signal-to-noise ratio (>100-fold induction). The resulting yeast genetic switches were readily integrated, in a plug-and-play manner, into an AND-gated carotenoid biosynthesis pathway.

Differential role of segments of α-mating factor secretion signal in Pichia pastoris towards granulocyte colony-stimulating factor emerging from a wild type or codon optimized copy of the gene

BACKGROUND

The methylotrophic yeast, Pichia pastoris has been widely used for the production of human therapeutics, but production of granulocyte colony-stimulating factor (G-CSF) in this yeast is low.The work reported here aimed to improve the extracellular production of G-CSF by introducing mutations in the leader sequence and using a codon optimized copy of G-CSF. Bioinformatic analysis was carried out to propose an explanation for observed effect of mutations on extracellular G-CSF production.

RESULTS

Mutations in the pro-region of the α-mating type (MAT) secretory signal, when placed next to a codon optimized (CO)-GCSF copy, specifically, the Δ57-70 type, led to highest G-CSF titre of 39.4 ± 1.4 mg/L. The enhanced effect of this deletion was also observed when it preceded the WT copy of the gene. Deletion of the 30-43 amino acids in the pro-peptide, fused with the wild type (WT)-GCSF copy, completely diminished G-CSF secretion, while no effect was observed when this deletion was in front of the CO-GCSF construct. Also, Matα:Δ47-49 deletion preceding the WT-GCSF dampened the secretion of this protein, while no effect was seen when this deletion preceded the CO-GCSF copy of the gene. This indicated that faster rates of translation (as achieved through codon optimization) could overcome the control exercised by these segments. The loss of secretion occurring due to Δ30-43 in the WT-GCSF was partially restored (by 60%) when the Δ57-70 was added. The effect of Δ47-49 segment in the WT-GCSF could also be partially restored (by 60%) by addition of Δ57-70 indicating the importance of the 47-49 region. A stimulatory effect of Δ57-70 was confirmed in the double deletion (Matα:Δ57-70;47-49) construct preceding the CO-GCSF. Secondary and tertiary structures, when predicted using I-TASSER, allowed to understand the relationship between structural changes and their impact on G-CSF secretion. The Δ57-70 amino acids form a major part of 3rd alpha-helix in the pre-pro peptide and its distortion increased the flexibility of the loop, thereby promoting its interaction with the cargo protein. A minimum loop length was found to be necessary for secretion. The strict control in the process of secretion appeared to be overcome by changing the secondary structures in the signal peptides. Such fine tuning can allow enhanced secretion of other therapeutics in this expression system.

CONCLUSIONS

Among the different truncations (Matα:Δ57-70, Matα:Δ47-49, Matα:Δ30-43, Matα:Δ57-70;30-43, Matα:Δ57-70;47-49) in pro-peptide of α-MAT secretion signal, Matα:Δ57-70 fused to CO-GCSF, led to highest G-CSF titre as compared to other Matα truncations. On the other hand, Matα:Δ30-43 and Matα:Δ47-49 fused to the WT-GCSF dampened the secretion of this protein indicating important role of these segments in the secretion of the cargo protein.

Pichia pastoris Protein Disulfide Isomerase (PDI1) promoter for heterologous protein production and its sequence characterization

Pichia pastoris (syn. Komagataella phaffii) expression system has been widely used in heterologous protein production. PDI1 is the structural gene for Protein Disulfide Isomerase (PDI) and one of the main proteins in the endoplasmic reticulum (ER). It serves as a chaperone and helps in the formation, restoration and isomerization of disulfide bonds in nascent proteins. Overexpression of chaperone genes like PDI1, is one of the approaches to alleviate unfolded protein response (UPR) in multicopy clones of P. pastoris. However, it is not in a general scheme and these approaches are protein specific. The complete understanding of promoter region of PDI1 can give insights for better regulation of UPR. The aim of our work was to characterize promoter region of PDI1 gene and evaluate the possibility of their use for efficient expression of heterologous proteins. For this purpose, we used a reporter system based on the Candida antarctica lipase B (CalB) gene. The efficiency of PDI1 promoter was also compared with that of inducible promoter, AOX1, and the constitutive promoter, GAP, under different carbon sources like glucose, glycerol and methanol. The results appear that the PDI1 promoter may act as an UPR inducible promoter at high copy numbers of target gene. Therefore, we propose that the PDI1 promoter can be used for moderate expression of heterologous proteins in pathway engineering applications and also for overexpression of molecular chaperones.

An investigation into gene copy number determination in transgenic yeast; The importance of selecting a reliable real-time PCR standard

Nowadays, Pichia pastoris is a well-known yeast for the production of recombinant proteins. The yield of protein production tightly depends on the copy number of the gene of interest into the host chromosome. Real-time PCR has been used as a high throughput method for molecular detection of gene copy number. In light of determining an absolute gene copy number, the reliability of the qPCR quantification standard is a major issue and it can be a potential source of errors in the final results. Since the literature on this issue is inconclusive, we set out to find a reliable quantification method that allows comparing results in different laboratories. We generated standard curves for two genomic loci (5'UTR AOX1 and ARG4) and for plasmid DNA carrying hGM-CSF coding sequence. These data was used to calculate the integrated hGM-CSFcDNA copy number in a recombinant P. pastoris clone. In our expriments the 5'UTR AOX1 gene showed a more accurate quantification standard, based on more efficient amplification and better reproducibility. The results obtained in this study showed that the differences in terms of structure and length between circular plasmid and linear gDNA could be the source of significant differences in the pattern of DNA amplification.

Pichia pastoris: A highly successful expression system for optimal synthesis of heterologous proteins

One of the most important branches of genetic engineering is the expression of recombinant proteins using biological expression systems. Nowadays, different expression systems are used for the production of recombinant proteins including bacteria, yeasts, molds, mammals, plants, and insects. Yeast expression systems such as Saccharomyces cerevisiae (S. cerevisiae) and Pichia pastoris (P. pastoris) are more popular. P. pastoris expression system is one of the most popular and standard tools for the production of recombinant protein in molecular biology. Overall, the benefits of protein production by P. pastoris system include appropriate folding (in the endoplasmic reticulum) and secretion (by Kex2 as signal peptidase) of recombinant proteins to the external environment of the cell. Moreover, in the P. pastoris expression system due to its limited production of endogenous secretory proteins, the purification of recombinant protein is easy. It is also considered a unique host for the expression of subunit vaccines which could significantly affect the growing market of medical biotechnology. Although P. pastoris expression systems are impressive and easy to use with well‐defined process protocols, some degree of process optimization is required to achieve maximum production of the target proteins. Methanol and sorbitol concentration, Mut forms, temperature and incubation time have to be adjusted to obtain optimal conditions, which might vary among different strains and externally expressed protein. Eventually, optimal conditions for the production of a recombinant protein in P. pastoris expression system differ according to the target protein.

Rationale-based selection of optimal operating strategies and gene dosage impact on recombinant protein production in Komagataella phaffii (Pichia pastoris)

Its features as a microbial and eukaryotic organism have turned Komagataella phaffii (Pichia pastoris) into an emerging cell factory for recombinant protein production (RPP). As a key step of the bioprocess development, this work aimed to demonstrate the importance of tailor designing the cultivation strategy according to the production kinetics of the cell factory. For this purpose, K. phaffii clones constitutively expressing (P_GAP) Candida rugosa lipase 1 (Crl1) with different gene dosage were used as models in continuous and fed‐batch cultures. Production parameters were much greater with a multicopy clone (MCC) than with the single‐copy clone (SCC). Regarding production kinetics, the specific product generation rate (q_P) increased linearly with increasing specific growth rate (µ) in SCC; by contrast, q_P exhibited saturation in MCC. A transcriptional analysis in chemostat cultures suggested the presence of eventual post‐transcriptional bottlenecks in MCC. After the strain characterization, in order to fulfil overall development of the bioprocess, the performance of both clones was also evaluated in fed‐batch mode. Strikingly, different optimal strategies were determined for both models due to the different production kinetic patterns observed as a trade‐off for product titre, yields and productivity. The combined effect of gene dosage and adequate µ enables rational process development with a view to optimize K. phaffii RPP bioprocesses.

Production of potent long-lasting consensus interferon using albumin fusion technology in Pichia pastoris expression system

Consensus interferon (cIFN) is a wholly synthetic therapeutic protein which is used to treat hepatitis C/B and certain types of malignancies. It has short serum half-life, therefore, to maintain its therapeutic level in the human body it requires thrice-weekly administration. Various strategies like PEGylation and micro-encapsulation have been developed during the last few years to enhance the pharmacokinetics of small therapeutic peptides. This study executed the human albumin-fusion technology, a simple and flexible approach to extend the serum circulating half-life of cIFN, because human serum albumin (HSA) has long circulating half-life (19 days) and very minute immunological activities. We integrated the codon-optimized HSA-cIFN fusion gene into Pichia pastoris genome by homologous recombination. The selection of hyper-resistant P. pastoris clone against Zeocin™ achieved a high-level secretory expression (250 mg/L) of fusion protein. HSA-cIFN fusion protein was purified using one-step purification by affinity chromatography with 34% recovery. The SDS-PAGE and SEC-HPLC analysis confirmed the final purified product has molecular weight of 87 kDa with 98% purity. Western blot analysis using anti-IFN antibodies further verified the purified HSA-cIFN fusion protein. The specific biological activity was 2.1 × 10⁶ IU/mg as assessed by cytopathic inhibition assay, and half-life of fusion protein was estimated by in vitro thermal and proteolytic stability studies. This work concludes that by using albumin fusion technology, codon optimization and one-step purification a high yield of 86 mg/L of biologically active protein with improved serum half-life was obtained.

Smoothing membrane protein structure determination by initial upstream stage improvements

Membrane proteins (MP) constitute 20–30% of all proteins encoded by the genome of various organisms and perform a wide range of essential biological functions. However, despite they represent the largest class of protein drug targets, a relatively small number high-resolution 3D structures have been obtained yet. Membrane protein biogenesis is more complex than that of the soluble proteins and its recombinant biosynthesis has been a major drawback, thus delaying their further structural characterization. Indeed, the major limitation in structure determination of MP is the low yield achieved in recombinant expression, usually coupled to low functionality, pinpointing the optimization target in recombinant MP research. Recently, the growing attention that have been dedicated to the upstream stage of MP bioprocesses allowed great advances, permitting the evolution of the number of MP solved structures. In this review, we analyse and discuss effective solutions and technical advances at the level of the upstream stage using prokaryotic and eukaryotic organisms foreseeing an increase in expression yields of correctly folded MP and that may facilitate the determination of their three-dimensional structure. A section on techniques used to protein quality control and further structure determination of MP is also included. Lastly, a critical assessment of major factors contributing for a good decision-making process related to the upstream stage of MP is presented.

Efficient Heterologous Production of Rhizopus oryzae Lipase via Optimization of Multiple Expression-Related Helper Proteins

This study is dedicated to efficiently produce Rhizopus oryzae lipase (ROL) by optimizing the expression of multiple expression-related helper proteins in Pichia pastoris. A series of engineered strains harboring different copy numbers of the ROL gene and different copies of the chaperone Pdi gene were first constructed to examine the influence of Pdi gene copy number on ROL production. The results showed that multiple copies of Pdi gene did not significantly improve ROL expression. Then, the effect of the co-overexpression of 10 expression-related helper proteins on ROL secretion was investigated by screening 20 colonies of each transformants. The data from shaking-flask fermentation suggested that Ssa4, Bmh2, Sso2, Pdi, Bip, Hac1, and VHb had positive effects on ROL expression. Subsequently, Ssa4, Bmh2, and Sso2, which all participate in vesicular trafficking and strongly promote ROL expression, were combined to further improve ROL production level. ROL activity of the screened strain GS115/5ROL-Ssa4-Sso2-Bmh2 4# attained 5230 U/mL. Furthermore, when the helper proteins Pdi, Bip, Hac1, and VHb were individually co-expressed with ROL in the strain GS115/5ROL-Ssa4-Sso2-Bmh2 4#, lipase activity increased to 5650 U/mL in the strain GS115/5ROL-Ssa4-Sso2-Bmh2-VHb 9#. Additionally, the maximum ROL activity of 41,700 U/mL was achieved in a 3 L bioreactor for high-density fermentation via a sorbitol–methanol co-feeding strategy, reaching almost twofold the value of the initial strain GS115/pAOα-5ROL 11#. Thus, the strategies in this study significantly increased ROL expression level, which is of great potential for the large-scale production of ROL in P. pastoris.

Efficient Production of Recombinant Protegrin-1 From Pichia pastoris, and Its Antimicrobial and in vitro Cell Migration Activity

Protegrin (PG) belongs to the antimicrobial peptide cathelicidin family. To date, five protegrin sequences have been identified in pigs, PG-1 to PG-5. Of these, PG-1 exhibits potent antimicrobial activity against a broad range of antibiotic-resistant microorganisms as well as viruses. However, the other potential role(s) of PG beyond antimicrobial has largely been unexplored. The aim of this study was to use nonpathogenic yeast Pichia pastoris to express antimicrobially active recombinant protegrin (rPG-1). Additionally, the effect of PG-1 on cell migration and proliferation was also examined in vitro using pig intestinal epithelial cells as a model. Highest level of rPG-1 (104 ± 11 μg/mL) was detected at 24 h in fermentation culture medium. Similar to rPG-1, 0.8 ± 0.10 g/L of proform PG-1 (rProPG-1) and 0.2 ± 0.02 g/L of the PG-1 cathelin domain (rCath) was detected in fermentation culture medium. Resulting recombinant PG-1 and cleaved rProPG-1 exerted antimicrobial activity against Escherichia coli DH5α at the same level as chemically synthesized PG-1. Enhanced cell migration was observed (p < 0.05) in groups treated with rProPG-1, rCath, and rPG-1 compared to the control. Furthermore, rPG-1 was stable at temperatures ranging from 25°C to 80°C. In summary, biologically active recombinant protegrin in its pro-, cathelin-, and mature- forms were successfully expressed in P. pastoris suggesting potential feasibility for future therapeutic applications.

Improving heterologous expression of porcine follicle-stimulating hormone in Pichia pastoris by integrating molecular strategies and culture condition optimization

Porcine follicle-stimulating hormone (pFSH), comprising α and β subunits, is commonly used to induce superovulation in domestic animals in assisted reproduction technologies; however, the practical application of pFSH is inhibited by the limited efficiency of its production. Recombinant yeast-derived FSH offers a practical alternative; however, the heterologous expression efficiency remains disappointingly low. To improve FSH production in Pichia pastoris, a series of molecular strategies, together with fermentation optimization, were tested in the present study. By comparing clones of the Mut^s phenotype strain, it was observed that the yield of soluble pFSH increased by approximately 96% in clones of the Mut⁺ phenotype strain. The protein levels of soluble pFSHβ, which confers biological specificity, increased by approximately 143 and 22% after two kinds of codon optimization strategies, respectively. Moreover, compared with the production of soluble pFSHβ and SUMO-pFSHβ, the production of soluble protein HSA-pFSHβ was significantly improved. Furthermore, the optimum pH and methanol concentration for expressing soluble HSA-pFSH in strain H3-3 were determined as 5.0-6.0 and 1.5-2% in shake-flask, and the yield of soluble HSA-pFSH could reach 40.8 mg/l after purification. In vitro bioactivity assays showed that recombinant HSA-pFSH could efficiently stimulate cAMP synthesis in HEK293 cells expressing porcine FSHR. In conclusion, our results demonstrated that the application of phenotypic selection of aox1 mutants, combined with codon optimization, the choice of fusion partners, and fermentation optimization, considerably increased the yield of pFSH in supernatant of P. pastoris and thus provided a valuable reference for the large-scale recombinant expression of pFSH.

New insight into the method of posttransformational vector amplification (PTVA) in Pichia pastoris

Posttransformational vector amplification (PTVA) is widely used to enrich the gene-copy number in Pichia pastoris. We engineered two test strains for PTVA studies and demonstrate that the PTVA process results in the amplification of a fragment with the resistant gene flanked by two homologous arms instead of the entire vector.

Improved production and characterization of Volvariella volvacea Endoglucanase 1 expressed in Pichia pastoris

Endoglucanase 1 (EG1) isolated from the straw mushroom has great potential in the textile and paper industries. Improving EG1 expression level will add to its value for industrial applications. In this study, we employed two combined strategies to enhance the expression quantity of EG1, which are increase the copy number of EG1 and enhance the folding and secretion efficiency of EG1 in the endoplasmic reticulum by overexpress HAC1. Multiple plasmids, which contains four copies of EG1, were constructed by isocaudamers, resulted a recombinant strain with EG1 activity up to 39.6 U/mL, 262% higher than that measured in the strain containing only a single copy. A significant increase in activity (151%) was found when eight copies of EG1 was introduced into a different host, compared with a host harboring four copies. Further overexpression of the HAC1 transcription factor in the host harboring eight EG1 copies led to activity of 91.9 U/mL, which is 619% higher than that measured in the original strain. Finally, EG1 activity of 650.1 U/mL was achieved in a 3-L scaled-up fed-batch fermenter and the protein yield was 4.05 g/L. The characteristics of recombinant EG1 were also investigated, the optimal values for enzyme activity were 60 °C and pH 5.0, which yielded a catalytic efficiency of 312.9 mL mg^-1min^-1 using carboxymethyl cellulose(CMC) as the substrate.

High-level extracellular production of Rhizopus oryzae lipase in Pichia pastoris via a strategy combining optimization of gene-copy number with co-expression of ERAD-related proteins

Rhizopus oryzae lipase (ROL) is an important industrial enzyme limited in application due to its low production in native strains. Here, we used a new combined strategy to overexpress ROL in Pichia pastoris. An efficient method based on bio-brick was developed to construct a series of vectors harboring different copy numbers of ROL gene cassettes, which were then transformed into P. pastoris GS115 to generate a strain with specific copy numbers of ROL. An optimized gene-dosage recombinant strain of GS115/pAOα-5ROL 11# harboring five copies of ROL was screened, revealing production of the highest activity (2700 U/mL), which was 8-fold higher than that of the strain harboring one copy. The activity of GS115/pAOα-5ROL 11# was then enhanced to 3080 U/mL in a shaking flask under optimized culture conditions. Subsequently, the endoplasmic reticulum-associated protein-degradation-related genes Ubc1 or/and Hrd1 were co-expressed with ROL to further increase ROL expression. The activities of the recombinant strains, GS115/5ROL-Ubc1 22#, -Hrd1 15#, and -Hrd1-Ubc1 1#, were 4000 U/mL, 4200 U/mL, and 4750 U/mL, which was 29.9%, 36.4%, and 54.2% higher, respectively, than that observed in GS115/pAOα-5ROL 11#. Using the combined strategy, ROL expression was improved 15.8-fold, with maximum GS115/5ROL-Hrd1-Ubc1 1# activity reaching 33,900 U/mL via a sorbitol/methanol co-feeding strategy in a 3-L fermenter and resulting in a 1.65-, 1.26-, and 1.14-fold enhancement relative to the activities observed in strains GS115/pAOα-5ROL 11#, GS115/5ROL-Ubc1 22#, and GS115/5ROL-Hrd1 15#, respectively. These results indicated that heterologous overexpression of ROL in P. pastoris using this combined strategy is feasible for large-scale industrialization.

Production and purification of chimeric HBc virus-like particles carrying influenza virus LAH domain as vaccine candidates

Background

The lack of a universal influenza vaccine is a global health problem. Interest is now focused on structurally conserved protein domains capable of eliciting protection against a broad range of influenza virus strains. The long alpha helix (LAH) is an attractive vaccine component since it is one of the most conserved influenza hemagglutinin (HA) stalk regions. For an improved immune response, the LAH domain from H3N2 strain has been incorporated into virus-like particles (VLPs) derived from hepatitis B virus core protein (HBc) using recently developed tandem core technology.

Results

Fermentation conditions for recombinant HBc-LAH were established in yeast Pichia pastoris and a rapid and efficient purification method for chimeric VLPs was developed to match the requirements for industrial scale-up. Purified VLPs induced strong antibody responses against both group 1 and group 2 HA proteins in mice.

Conclusion

Our results indicate that the tandem core technology is a useful tool for incorporation of highly hydrophobic LAH domain into HBc VLPs. Chimeric VLPs can be successfully produced in bioreactor using yeast expression system. Immunologic data indicate that HBc VLPs carrying the LAH antigen represent a promising universal influenza vaccine component.

Electronic supplementary material

The online version of this article (10.1186/s12896-017-0396-8) contains supplementary material, which is available to authorized users.

Cellobiohydrolase B of Aspergillus niger over-expressed in Pichia pastoris stimulates hydrolysis of oil palm empty fruit bunches

BACKGROUND

Aspergillus niger, along with many other lignocellulolytic fungi, has been widely used as a commercial workhorse for cellulase production. A fungal cellulase system generally includes three major classes of enzymes i.e., β-glucosidases, endoglucanases and cellobiohydrolases. Cellobiohydrolases (CBH) are vital to the degradation of crystalline cellulose present in lignocellulosic biomass. However, A. niger naturally secretes low levels of CBH. Hence, recombinant production of A. niger CBH is desirable to increase CBH production yield and also to allow biochemical characterisation of the recombinant CBH from A. niger.

METHODS

In this study, the gene encoding a cellobiohydrolase B (cbhB) from A. niger ATCC 10574 was cloned and expressed in the methylotrophic yeast Pichia pastoris X-33. The recombinant CBHB was purified and characterised to study its biochemical and kinetic characteristics. To evaluate the potential of CBHB in assisting biomass conversion, CBHB was supplemented into a commercial cellulase preparation (Cellic^® CTec2) and was used to hydrolyse oil palm empty fruit bunch (OPEFB), one of the most abundant lignocellulosic waste from the palm oil industry. To attain maximum saccharification, enzyme loadings were optimised by response surface methodology and the optimum point was validated experimentally. Hydrolysed OPEFB samples were analysed using attenuated total reflectance FTIR spectroscopy (ATR-FTIR) to screen for any compositional changes upon enzymatic treatment.

RESULTS

Recombinant CBHB was over-expressed as a hyperglycosylated protein attached to N-glycans. CBHB was enzymatically active towards soluble substrates such as 4-methylumbelliferyl-β-D-cellobioside (MUC), p-nitrophenyl-cellobioside (pNPC) and p-nitrophenyl-cellobiotrioside (pNPG3) but was not active towards crystalline substrates like Avicel^® and Sigmacell cellulose. Characterisation of purified CBHB using MUC as the model substrate revealed that optimum catalysis occurred at 50 °C and pH 4 but the enzyme was stable between pH 3 to 10 and 30 to 80 °C. Although CBHB on its own was unable to digest crystalline substrates, supplementation of CBHB (0.37%) with Cellic^® CTec2 (30%) increased saccharification of OPEFB by 27%. Compositional analyses of the treated OPEFB samples revealed that CBHB supplementation reduced peak intensities of both crystalline cellulose Iα and Iβ in the treated OPEFB samples.

DISCUSSION

Since CBHB alone was inactive against crystalline cellulose, these data suggested that it might work synergistically with other components of Cellic^® CTec2. CBHB supplements were desirable as they further increased hydrolysis of OPEFB when the performance of Cellic^® CTec2 was theoretically capped at an enzyme loading of 34% in this study. Hence, A. niger CBHB was identified as a potential supplementary enzyme for the enzymatic hydrolysis of OPEFB.

Recycling of a selectable marker with a self-excisable plasmid in Pichia pastoris

Pichia pastoris is a widely used heterologous protein production workhorse. However, with its multiple genetic modifications to solve bottlenecks for heterologous protein productivity, P. pastoris lacks selectable markers. Existing selectable marker recycling plasmids have drawbacks (e.g., slow growth and conditional lethality). Here, zeocin-resistance marker recycling vectors were constructed using the Cre/loxP recombination system. The vectors were used to (i) knock in heterologous phytase, xylanase and lipase expression cassettes, (ii) increase the phytase, xylanase and lipase gene copy number to 13, 5, and 5, respectively, with vector introduction and (iii) engineer the secretion pathway by co-overexpressing secretion helper factors (Sly1p and Sec1p) without introducing selectable markers, giving a phytase field of 0.833 g/L. The vectors allow selectable marker recycling and would be a useful tool to engineer P. pastoris for high heterologous protein productivity.

Enhancement of recombinant BmK AngM1 production in Pichia pastoris by regulating gene dosage, co-expressing with chaperones and fermenting in fed-batch mode

The scorpion peptide BmK AngM1 was reported to exhibit evident analgesic effect, but its yield by extraction from scorpion venom limits the research and application. The heterologous expression of BmK AngM1 was achieved in Pichia pastoris in our previous study. In order to realize high-level expression of recombinant BmK AngM1 (rBmK AngM1), the gene dosage of BmK AngM1 was optimized in engineered strains. The yield of rBmK AngM1 in the four-copy strain reached up to 100 mg/L, which was further enhanced to 190 mg/L by co-expressing with chaperones of PDI, BiP, and HAC1. Moreover, the yield of rBmK AngM1 was up to 1200 mg/L by high-density fermentation in 10 L fermenter. Finally, 360 mg rBmK AngM1 was purified from 1 L cultures by a two-step purification method. The efficient and convenient techniques presented in this study could facilitate further scale-up for industrial production of rBmK AngM1.

Production of Chimeric Acidic α-Amylase by the Recombinant Pichia pastoris and Its Applications

Recombinant chimeric α-amylase (Ba-Gt-amy) has been produced extracellularly in Pichia pastoris under AOX promoter. Clones of P. pastoris with multiple gene copies have been generated by multiple transformations and post-transformational vector amplification, which led to 10.7-fold enhancement in α-amylase titre as compared to a clone with a copy of the gene. The recombinant P. pastoris integrated eight copies of Ba-Gt-amy in the genome of P. pastoris, as revealed by real time PCR data analysis. Heterologous protein expression as well as mRNA level of Ba-Gt-amy was higher in multi-copy clone than that with single copy. The pure Ba-Gt-amy expressed in P. pastoris is a glycoprotein of 75 kDa, which is optimally active at pH 4.0 and 60°C with T_1/2 of 40 min at 70°C. The Kinetic parameters and end product analysis suggested that glycosylation has no effect on catalytic properties of Ba-Gt-amy. The enzyme saccharifies soluble as well as raw starches efficiently and generates maltose and maltooligosaccharides, thus, useful in baking and sugar syrup industries. The strategy for generating multi-copy clones is being reported for the first time, which could be useful in enhancing the production of other recombinant proteins.

Bioactivity studies of Huh-7 cells derived human epidermal growth factor expressed in Pichia pastoris

Previously, we have reported cloning of human epidermal growth factor gene from Huh-7 cells and its extracellular expression in Pichia pastoris. The presented work is a detailed report regarding molecular characterization of Huh-7 cells-derived hEGF expressed in Pichia pastoris with special reference to its glycosylation profiling and bioactivity studies. Densitometric scanning of SDS-PAGE separated extracellular proteins from hEGF recombinant Pichia pastoris strain indicated that about 84% of the extracellular proteins were glycosylated. Size exclusion chromatography using Superdex 75 prep grade column was successfully utilized to separate fractions containing glycosylated and non-glycosylated extracellular proteins. In dot blot assay, hEGF was detected in both glycosylated and non-glycosylated fractions. Bioactivity assays revealed that both glycosylated and non-glycosylated fractions were bioactive as determined by cell viability assay. It was also observed that hEGF present in non-glycosylated fraction was relatively more bioactive than hEGF present in glycosylated fraction.

Single amino acid substitutions in the selectivity filter render NbXIP1;1α aquaporin water permeable

BACKGROUND

Aquaporins (AQPs) are integral membrane proteins that facilitate transport of water and/or other small neutral solutes across membranes in all forms of life. The X Intrinsic Proteins (XIPs) are the most recently recognized and the least characterized aquaporin subfamily in higher plants. XIP1s have been shown to be impermeable to water but permeable to boric acid, glycerol, hydrogen peroxide and urea. However, uncertainty regarding the determinants for selectivity and lack of an activity that is easy to quantify have hindered functional investigations. In an effort to resolve these issues, we set out to introduce water permeability in Nicotiana benthamiana XIP1;1α (NbXIP1;1α), by exchanging amino acid residues of predicted alternative aromatic/arginine (ar/R) selectivity filters of NbXIP1;1α for residues constituting the water permeable ar/R selectivity filter of AtTIP2;1.

RESULTS

Here, we present functional results regarding the amino acid substitutions in the putative filters as well as deletions in loops C and D of NbXIP1;1α. In addition, homology models were created based on the high resolution X-ray structure of AtTIP2;1 to rationalize the functional properties of wild-type and mutant NbXIP1;1α. Our results favour Thr 246 rather than Val 242 as the residue at the helix 5 position in the ar/R filter of NbXIP1;1α and indicate that the pore is not occluded by the loops when heterologously expressed in Pichia pastoris. Moreover, our results show that a single amino acid substitution in helix 1 (L79G) or in helix 2 (I102H) is sufficient to render NbXIP1;1α water permeable. Most of the functional results can be rationalized from the models based on a combination of aperture and hydrophobicity of the ar/R filter.

CONCLUSION

The water permeable NbXIP1;1α mutants imply that the heterologously expressed proteins are correctly folded and offer means to explore the structural and functional properties of NbXIP1;1α. Our results support that Thr 246 is part of the ar/R filter. Furthermore, we suggest that a salt bridge to an acidic residue in helix 1, conserved among the XIPs in clade B, directs the orientation of the arginine in the ar/R selectivity filter and provides a novel approach to tune the selectivity of AQPs.

Potential of Pichia pastoris for the production of industrial penicillin G acylase

This study deals with the potential of Pichia pastoris X-33 for the production of penicillin G acylase (PGA^A) from Achromobacter sp. CCM 4824. Synthetic gene matching the codon usage of P. pastoris was designed for intracellular and secretion-based production strategies and cloned into vectors pPICZ and pPICZα under the control of AOX1 promoter. The simple method was developed to screen Pichia transformants with the intracellularly produced enzyme. The positive correlation between acylase production and pga gene dosage for both expression systems was demonstrated in small scale experiments. In fed-batch bioreactor cultures of X-33/PENS2, an extracellular expression system, total PGA^A expressed from five copies reached 14,880 U/L of an active enzyme after 142 h; however, 60% of this amount retained in the cytosol. The maximum PGA^A production of 31,000 U/L was achieved intracellularly from nine integrated gene copies of X-33/PINS2 after 90 h under methanol induction. The results indicate that in both expression systems the production level of PGA^A is similar but there is a limitation in secretion efficiency.

The N-terminal Ankyrin Repeat Domain Is Not Required for Electrophile and Heat Activation of the Purified Mosquito TRPA1 Receptor

Temperature sensors are crucial for animals to optimize living conditions. The temperature response of the ion channel transient receptor potential A1 (TRPA1) is intriguing; some orthologs have been reported to be activated by cold and others by heat, but the molecular mechanisms responsible for its activation remain elusive. Single-channel electrophysiological recordings of heterologously expressed and purified Anopheles gambiae TRPA1 (AgTRPA1), with and without the N-terminal ankyrin repeat domain, demonstrate that both proteins are functional because they responded to the electrophilic compounds allyl isothiocyanate and cinnamaldehyde as well as heat. The proteins' similar intrinsic fluorescence properties and corresponding quenching when activated by allyl isothiocyanate or heat suggest lipid bilayer-independent conformational changes outside the N-terminal domain. The results show that AgTRPA1 is an inherent thermo- and chemoreceptor, and analogous to what has been reported for the human TRPA1 ortholog, the N-terminal domain may tune the response but is not required for the activation by these stimuli.

Cloning, expression, and characterization of Aureobasidium melanogenum lipase in Pichia pastoris

cDNA of Aureobasidium melanogenum lipase comprises 1254 bp encoding 417 amino acids, whereas genomic DNA of lipase comprises 1311 bp with one intron (57 bp). The lipase gene contains a putative signal peptide encoding 26 amino acids. The A. melanogenum lipase gene was successfully expressed in Pichia pastoris. Recombinant lipase in an inducible expression system showed the highest lipase activity of 3.8 U/mL after six days of 2% v/v methanol induction. The molecular mass of purified recombinant lipase was estimated as 39 kDa using SDS-PAGE. Optimal lipase activity was observed at 35–37 °C and pH 7.0 using p-nitrophenyl laurate as the substrate. Lipase activity was enhanced by Mg2+, Mn2+, Li+, Ca2+, Ni2+, CHAPS, DTT, and EDTA and inhibited by Hg2+, Ag+, SDS, Tween 20, and Triton X-100. The addition of 10% v/v acetone, DMSO, p-xylene, and octanol increased lipase activity, whereas that of propanol and butanol strongly inhibited it.

Overexpressing target helper genes enhances secretion and glycosylation of recombinant proteins in Pichia pastoris under simulated microgravity

In this study, the potential helper genes were identified through the data analysis of transcriptomic and proteomic profiling in recombinant Pichia pastoris cultured under simulated microgravity (SMG). Co-expressing of four genes PRX1, YAP1, AHA1, and YPT6, involved in the oxidative stress response and protein folding, exhibited promising helper factor effects on the recombinant protein yields in engineered P. pastoris, respectively. When two of the above genes were co-expressed simultaneously, β-glucuronidase (PGUS) specific activity was further increased by 30.3-50.6 % comparing with that of single helper gene, particularly when the oxidative stress response and protein folding genes were both present in the combinations. In addition, co-expressing co-chaperone AHA1 and transcription factor YAP1 not only enhanced PGUS secretion, but also affected its glycosylation. Thus, through deep "omics" analysis of SMG effects, our results provided combined impact of new helper factors to improve the efficacy of recombinant protein secretion and glycosylation in engineered P. pastoris.

Integrated Approach To Producing High-Purity Trehalose from Maltose by the Yeast Yarrowia lipolytica Displaying Trehalose Synthase (TreS) on the Cell Surface

An alternative strategy that integrated enzyme production, trehalose biotransformation, and bioremoval in one bioreactor was developed in this study, thus simplifying the traditional procedures used for trehalose production. The trehalose synthase gene from a thermophilic archaea, Picrophilus torridus, was first fused to the YlPir1 anchor gene and then inserted into the genome of Yarrowia lipolytica, thus yielding an engineered yeast strain. The trehalose yield reached 73% under optimal conditions. The thermal and pH stabilities of the displayed enzyme were improved compared to those of its free form purified from recombinant Escherichia coli. After biotransformation, the glucose byproduct and residual maltose were directly fermented to ethanol by a Saccharomyces cerevisiae strain. Ethanol can be separated by distillation, and high-purity trehalose can easily be obtained from the fermentation broth. The results show that this one-pot procedure is an efficient approach to the economical production of trehalose from maltose.

Molecular optimization of rabies virus glycoprotein expression in Pichia pastoris

In this work, different approaches were investigated to enhance the expression rabies virus glycoprotein (RABV-G) in the yeast Pichia pastoris; this membrane protein is responsible for the synthesis of rabies neutralizing antibodies. First, the impact of synonymous codon usage bias was examined and an optimized RABV-G gene was synthesized. Nevertheless, data showed that the secretion of the optimized RABV-G gene was not tremendously increased as compared with the non-optimized one. In addition, similar levels of RABV-G were obtained when α-factor mating factor from Saccharomyces cerevisiae or the acid phosphatase PHO1 was used as a secretion signal. Therefore, sequence optimization and secretion signal were not the major bottlenecks for high-level expression of RABV-G in P. pastoris. Unfolded protein response (UPR) was induced in clones containing high copy number of RABV-G expression cassette indicating that folding was the limiting step for RABV-G secretion. To circumvent this limitation, co-overexpression of five factors involved in oxidative protein folding was investigated. Among these factors only PDI1, ERO1 and GPX1 proved their benefit to enhance the expression. The highest expression level of RABV-G reached 1230 ng ml(-1). Competitive neutralizing assay confirmed that the recombinant protein was produced in the correct conformational form in this host.

Secretory production of designed multipeptides displayed on a thermostable bacterial thioredoxin scaffold in Pichia pastoris

Internal grafting of designed peptides to scaffold proteins is a valuable strategy for a variety of applications including recombinant peptide antigen construction. A peptide epitope from human papillomavirus (HPV) minor capsid protein L2 displayed on thioredoxin (Trx) has been validated preclinically as a broadly protective and low-cost alternative HPV vaccine. Focusing on thioredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus (PfTrx) as a scaffold, we have constructed a modified Pichia pastoris expression vector and used a PfTrx fusion derivative containing three tandemly repeated copies of a 19 amino acids peptide epitope from HPV-L2 for expression optimization and biochemical-immunological characterization of the Pichia-produced PfTrx-L2 antigen. We show that PfTrx-L2 is produced at high levels (up to 100 mg from a 100 ml starting culture using a multi-cycle induction protocol) and secreted into the culture medium as a highly enriched (>70% pure), non-glycosylated polypeptide that can be purified to homogeneity in a single step. Oxidation and aggregation state, thermal stability and immunogenicity of the endotoxin-free PfTrx-L2 antigen produced in P. pastoris were tested and found to be identical to those of the same antigen produced in Escherichia coli. Secretory production of endotoxin-free PfTrx-peptides in P. pastoris represents a cost- and time-effective alternative to E. coli production. Specifically designed for peptide antigens, the PfTrx-expression vector and conditions described herein are easily transferable to a variety of applications centred on the use of structurally constrained bioactive peptides as immune as well as target-specific binder reagents.