An improved method for enhanced production and biological activity of human secretory leukocyte protease inhibitor (SLPI) in Pichia pastoris

Synthesis of secretory leukocyte protease inhibitor using cell-free protein synthesis system

Secretory leukocyte protease inhibitor (SLPI) functions as a protease inhibitor that modulates excessive proteolysis in the body, exhibits broad-spectrum antimicrobial activity, regulates inflammatory responses, and plays an important role in the innate immunity. The purpose of the study was to artificially synthesize a SLPI, an antimicrobial peptide, and investigate its effect on antimicrobial activity against Porphyromonas gingivalis and interleukin-6 (IL-6) production. SLPI protein with a molecular weight of approximately 13 kDa was artificially synthesized using a cell-free protein synthesis (CFPS) system and investigated by western blotting and enzyme-linked immunosorbent assay (ELISA). Disulfide bond isomerase in the protein synthesis mixture increased the amount of SLPI synthesized. The synthesized SLPI (sSLPI) protein was purified and its antimicrobial activity was investigated based on the growth of Porphyromonas gingivalis and bacterial adhesion to oral epithelial cells. The effect of sSLPI on IL-6 production in human periodontal ligament fibroblasts (HPLFs) was examined by ELISA. Our results showed that sSLPI significantly inhibited the growth of Porphyromonas gingivalis and bacterial adhesion to oral epithelial cells and further inhibited IL-6 production by HPLFs. These results suggested that SLPI artificially synthesized using the CFPS system may play a role in the prevention of periodontal diseases through its antimicrobial and anti-inflammatory effects.

The secretory leukocyte protease inhibitor (SLPI) in pathophysiology of non-communicable diseases: Evidence from experimental studies to clinical applications

Non-communicable diseases (NCDs) are a worldwide health issue because of their prevalence, negative impacts on human welfare, and economic costs. Protease enzymes play important roles in viral and NCD diseases. Slowing disease progression by inhibiting proteases using small-molecule inhibitors or endogenous inhibitory peptides appears to be crucial. Secretory leukocyte protease inhibitor (SLPI), an inflammatory serine protease inhibitor, maintains protease/antiprotease balance. SLPI is produced by host defense effector cells during inflammation to prevent proteolytic enzyme-induced tissue damage. The etiology of noncommunicable illnesses is linked to SLPI's immunomodulatory and tissue regeneration roles. Disease phases are associated with SLPI levels and activity changes in regional tissue and circulation. SLPI has been extensively evaluated in inflammation, but rarely in NCDs. Unfortunately, the thorough evaluation of SLPI's pathophysiological functions in NCDs in multiple research models has not been published elsewhere. In this review, data from PubMed from 2014 to 2023 was collected, analysed, and categorized into in vitro, in vivo, and clinical studies. According to the review, serine protease inhibitor (SLPI) activity control is linked to non-communicable diseases (NCDs) and other illnesses. Overexpression of the SLPI gene and protein may be a viable diagnostic and therapeutic target for non-communicable diseases (NCDs). SLPI is also cytoprotective, making it a unique treatment. These findings suggest that future research should focus on these pathways using advanced methods, reliable biomarkers, and therapy approaches to assess susceptibility and illness progression. Implications from this review will help pave the way for a new therapeutic target and diagnosis marker for non-communicable diseases.

Current achievements, strategies, obstacles, and overcoming the challenges of the protein engineering in Pichia pastoris expression system

Yeasts serve as exceptional hosts in the manufacturing of functional protein engineering and possess industrial or medical utilities. Considerable focus has been directed towards yeast owing to its inherent benefits and recent advancements in this particular cellular host. The Pichia pastoris expression system is widely recognized as a prominent and widely accepted instrument in molecular biology for the purpose of generating recombinant proteins. The advantages of utilizing the P. pastoris system for protein production encompass the proper folding process occurring within the endoplasmic reticulum (ER), as well as the subsequent secretion mediated by Kex2 as a signal peptidase, ultimately leading to the release of recombinant proteins into the extracellular environment of the cell. In addition, within the P. pastoris expression system, the ease of purifying recombinant protein arises from its restricted synthesis of endogenous secretory proteins. Despite its achievements, scientists often encounter persistent challenges when attempting to utilize yeast for the production of recombinant proteins. This review is dedicated to discussing the current achievements in the usage of P. pastoris as an expression host. Furthermore, it sheds light on the strategies employed in the expression system and the optimization and development of the fermentative process of this yeast. Finally, the impediments (such as identifying high expression strains, improving secretion efficiency, and decreasing hyperglycosylation) and successful resolution of certain difficulties are put forth and deliberated upon in order to assist and promote the expression of complex proteins in this prevalent recombinant host.

The effect of the bgs13 mutation on the structure of the reporter protein beta-lactoglobulin: Influence on folding and aggregation in Pichia pastoris

Pichia pastoris, a methylotrophic yeast used for recombinant protein expression, has the capability of performing many eukaryotic post-translational modifications, growing to high cell densities, and producing proteins in a cost-effective manner. However, P. pastoris's secretion properties are not always efficient, and its secretory pathway mechanisms have not been thoroughly elucidated. A previously identified mutant strain, bgs13, was found to efficiently secrete most recombinant proteins tested, raising the possibility that this bgs13 mutant is a universal super secreter. In this study, we used a reporter protein, β-lactoglobulin (b-LG), to perform structural analysis of the protein secreted from wild type and mutant bgs13 strains to investigate the secretory mechanism. Primary, secondary, and tertiary structures of b-LG were examined using Edman sequencing, circular dichroism, tryptophan fluorescence, and temperature induced aggregation analysis. Our results demonstrate that the bgs13 produced more b-LG than the wt strain and that this protein was functionally folded similar to the wt. Surprisingly, we also found that the bgs13 b-LG was more resistant to aggregation, providing another example of the superior qualities of this strain for enhanced secreted protein production.

Pathway engineering facilitates efficient protein expression in Pichia pastoris

Pichia pastoris has been recognized as an important platform for the production of various heterologous proteins in recent years. The strong promoter AOX1, induced by methanol, with the help of the α-pre-pro signal sequence, can lead to a high expression level of extracellular protein. However, this combination was not always efficient, as protein secretion in P. pastoris involves numerous procedures mediated by several cellular proteins, including folding assisted by endoplasmic reticulum (ER) molecular chaperones, degradation through ubiquitination, and an efficient vesicular transport system. Efficient protein expression requires the cooperation of various intracellular pathways. This article summarizes the process of protein secretion, modification, and transportation in P. pastoris. In addition, the roles played by the key proteins in these processes and the corresponding co-expression effects are also listed. It is expected to lay the foundation for the industrial protein production of P. pastoris. KEY POINTS: • Mechanisms of chaperones in protein folding and their co-expression effects are summarized. • Protein glycosylation modifications are comprehensively reviewed. • Current dilemmas in the overall protein secretion pathway of Pichia pastoris and corresponding solutions are demonstrated.

Murine Factor H Co-Produced in Yeast With Protein Disulfide Isomerase Ameliorated C3 Dysregulation in Factor H-Deficient Mice

Recombinant human factor H (hFH) has potential for treating diseases linked to aberrant complement regulation including C3 glomerulopathy (C3G) and dry age-related macular degeneration. Murine FH (mFH), produced in the same host, is useful for pre-clinical investigations in mouse models of disease. An abundance of FH in plasma suggests high doses, and hence microbial production, will be needed. Previously, Pichia pastoris produced useful but modest quantities of hFH. Herein, a similar strategy yielded miniscule quantities of mFH. Since FH has 40 disulfide bonds, we created a P. pastoris strain containing a methanol-inducible codon-modified gene for protein-disulfide isomerase (PDI) and transformed this with codon-modified DNA encoding mFH under the same promoter. What had been barely detectable yields of mFH became multiple 10s of mg/L. Our PDI-overexpressing strain also boosted hFH overproduction, by about tenfold. These enhancements exceeded PDI-related production gains reported for other proteins, all of which contain fewer disulfide-stabilized domains. We optimized fermentation conditions, purified recombinant mFH, enzymatically trimmed down its (non-human) N-glycans, characterised its functions in vitro and administered it to mice. In FH-knockout mice, our de-glycosylated recombinant mFH had a shorter half-life and induced more anti-mFH antibodies than mouse serum-derived, natively glycosylated, mFH. Even sequential daily injections of recombinant mFH failed to restore wild-type levels of FH and C3 in mouse plasma beyond 24 hours after the first injection. Nevertheless, mFH functionality appeared to persist in the glomerular basement membrane because C3-fragment deposition here, a hallmark of C3G, remained significantly reduced throughout and beyond the ten-day dosing regimen.

Defining the mechanism of PDI interaction with disulfide-free amyloidogenic proteins: Implications for exogenous protein expression and neurodegenerative disease

Protein disulfide isomerase (PDI) is an important molecular chaperone capable of facilitating protein folding in addition to catalyzing the formation of a disulfide bond. To better understand the distinct substrate-screening principles of Pichia pastoris PDI (Protein disulfide isomerase) and the protective role of PDI in amyloidogenic diseases, we investigated the expression abundance and intracellular retention levels of three archetypal amyloidogenic disulfide bond-free proteins (Aβ42, α-synuclein (α-Syn) and SAA1) in P. pastoris GS115 strain without and with the overexpression of PpPDI (P. pastoris PDI). Intriguingly, amyloidogenic Aβ42 and α-Syn were detected only as intracellular proteins whereas amyloidogenic SAA1 was detected both as intracellular and extracellular proteins when these proteins were expressed in the PpPDI-overexpressing GS115 strain. The binding between PpPDI and each of the three amyloidogenic proteins was investigated by molecular docking and simulations. Three different patterns of PpPDI-substrate complexes were observed, suggesting that multiple modes of binding might exist for the binding between PpPDI and its amyloidogenic protein substrates, and this could represent different specificities and affinities of PpPDI toward its substrates. Further analysis of the proteomics data and functional annotations indicated that PpPDI could eliminate the need for misfolded proteins to be partitioned in ER-associated compartments.

Overcoming Obstacles in Protein Expression in the Yeast Pichia pastoris: Interviews of Leaders in the Pichia Field

The yeast Pichia pastoris (also known as Komagataella pastoris) has been used for over 30 years to produce thousands of valuable, heterologous proteins, such as insulin to treat diabetes and antibodies to prevent migraine headaches. Despite its success, there are some common, stubborn problems encountered by research scientists when they try to use the yeast to produce their recombinant proteins. In order to provide those working in this field with strategies to overcome these common obstacles, nine experts in P. pastoris protein expression field were interviewed to create a written review and video (https://www.youtube.com/watch?v=Q1oD6k8CdG8). This review describes how each respected scientist addressed a specific challenge, such as identifying high expression strains, improving secretion efficiency and decreasing hyperglycosylation. Their perspective and practical advice can be a tool to help empower others to express challenging proteins in this popular recombinant host.

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.

Role of BGS13 in the Secretory Mechanism of Pichia pastoris

The methylotrophic yeast Pichia pastoris has been utilized for heterologous protein expression for over 30 years. Because P. pastoris secretes few of its own proteins, the exported recombinant protein is the major polypeptide in the extracellular medium, making purification relatively easy. Unfortunately, some recombinant proteins intended for secretion are retained within the cell. A mutant strain isolated in our laboratory, containing a disruption of the BGS13 gene, displayed elevated levels of secretion for a variety of reporter proteins. The Bgs13 peptide (Bgs13p) is similar to the Saccharomyces cerevisiae protein kinase C 1 protein (Pkc1p), but its specific mode of action is currently unclear. To illuminate differences in the secretion mechanism between the wild-type (wt) strain and the bgs13 strain, we determined that the disrupted bgs13 gene expressed a truncated protein that had reduced protein kinase C activity and a different location in the cell, compared to the wt protein. Because the Pkc1p of baker's yeast plays a significant role in cell wall integrity, we investigated the sensitivity of the mutant strain's cell wall to growth antagonists and extraction by dithiothreitol, determining that the bgs13 strain cell wall suffered from inherent structural problems although its porosity was normal. A proteomic investigation of the bgs13 strain secretome and cell wall-extracted peptides demonstrated that, compared to its wt parent, the bgs13 strain also displayed increased release of an array of normally secreted, endogenous proteins, as well as endoplasmic reticulum-resident chaperone proteins, suggesting that Bgs13p helps regulate the unfolded protein response and protein sorting on a global scale.IMPORTANCE The yeast Pichia pastoris is used as a host system for the expression of recombinant proteins. Many of these products, including antibodies, vaccine antigens, and therapeutic proteins such as insulin, are currently on the market or in late stages of development. However, one major weakness is that sometimes these proteins are not secreted from the yeast cell efficiently, which impedes and raises the cost of purification of these vital proteins. Our laboratory has isolated a mutant strain of Pichia pastoris that shows enhanced secretion of many proteins. The mutant produces a modified version of Bgs13p. Our goal is to understand how the change in the Bgs13p function leads to improved secretion. Once the Bgs13p mechanism is illuminated, we should be able to apply this understanding to engineer new P. pastoris strains that efficiently produce and secrete life-saving recombinant proteins, providing medical and economic benefits.

Production Optimization of an Active β-Galactosidase of Bifidobacterium animalis in Heterologous Expression Systems

β-Galactosidase (E.C.3.2.1.23) catalyzes the hydrolysis of lactose into glucose and galactose and the synthesis of galacto-oligosaccharides as well. The β-galactosidases from bacteria, especially lactobacilli, and yeast have neutral pH and are much more likely to be developed as food additives. However, the challenges of cumbersome purification, product toxicity, and low yield in protein production have limited the commercialization of many excellent candidates. In this study, we identified a β-galactosidase gene (bg42-106) in Bifidobacterium animalis ACCC05790 and expressed the gene product in Escherichia coli BL21(DE3) and Pichia pastoris GS115, respectively. The recombinant bG42-106 purified from E. coli cells was found to be optimally active at pH 6.0 and 60°C and had excellent stability over a wide pH range (5.0–8.0) and at high temperature (60°C). The specific activity of bG42-106 reached up to 2351 U/mg under optimal conditions. The galacto-oligosaccharide yield was 24.45 g/L after incubation with bG42-106 at 60°C for 2 h. When recombinant bG42-106 was expressed in Pichia pastoris GS115, it was found in the culture medium but only at a concentration of 1.73 U/ml. To increase its production, three strategies were employed, including codon optimization, disulfide formation, and fusion with a Cherry tag, with Cherry-tag fusion being most effective. The culture medium of P. pastoris that expressed Cherry-tagged bG42-106 contained 24.4 U/mL of β-galactosidase activity, which is 14-fold greater than that produced by culture of P. pastoris harboring wild-type bG42-106.

Recombinant Inga Laurina Trypsin Inhibitor (ILTI) Production in Komagataella Phaffii Confirms Its Potential Anti-Biofilm Effect and Reveals an Anti-Tumoral Activity

Protease inhibitors have a broad biotechnological application ranging from medical drugs to anti-microbial agents. The Inga laurina trypsin inhibitor (ILTI) previously showed a great in vitro inhibitory effect under the adherence of Staphylococcus species, being a strong candidate for use as an anti-biofilm agent. Nevertheless, this is found in small quantities in its sources, which impairs its utilization at an industrial scale. Within this context, heterologous production using recombinant microorganisms is one of the best options to scale up the recombinant protein production. Thus, this work aimed at utilizing Komagataella phaffii to produce recombinant ILTI. For this, the vector pPIC9K+ILTI was constructed and inserted into the genome of the yeast K. phaffii, strain GS115. The protein expression was highest after 48 h using methanol 1%. A matrix-assisted laser desorption ionization⁻time-of-flight (MALDI⁻TOF) analysis was performed to confirm the production of the recombinant ILTI and its activity was investigated trough inhibitory assays using the synthetic substrate Nα-Benzoyl-D,L-arginine p-nitroanilide hydrochloride (BAPNA). Finally, recombinant ILTI (rILTI) was used in assays, showing that there was no significant difference between native and recombinant ILTI in its inhibitory activity in biofilm formation. Anti-tumor assay against Ehrlich ascites tumor (EAT) cells showed that rILTI has a potential anti-tumoral effect, showing the same effect as Melittin when incubated for 48 h in concentrations above 25 µg/mL. All together the results suggests broad applications for rILTI.

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.

Activated microglia/macrophage whey acidic protein (AMWAP) inhibits NFκB signaling and induces a neuroprotective phenotype in microglia

BACKGROUND

Microglia reactivity is a hallmark of neurodegenerative diseases. We have previously identified activated microglia/macrophage whey acidic protein (AMWAP) as a counter-regulator of pro-inflammatory response. Here, we studied its mechanisms of action with a focus on toll-like receptor (TLR) and nuclear factor κB (NFκB) signaling.

METHODS

Recombinant AMWAP was produced in Escherichia coli and HEK293 EBNA cells and purified by affinity chromatography. AMWAP uptake was identified by fluorescent labeling, and pro-inflammatory microglia markers were measured by qRT-PCR after stimulation with TLR ligands. NFκB pathway proteins were assessed by immunocytochemistry, Western blot, and immunoprecipitation. A 20S proteasome activity assay was used to investigate the anti-peptidase activity of AMWAP. Microglial neurotoxicity was estimated by nitrite measurement and quantification of caspase 3/7 levels in 661W photoreceptors cultured in the presence of microglia-conditioned medium. Microglial proliferation was investigated using flow cytometry, and their phagocytosis was monitored by the uptake of 661W photoreceptor debris.

RESULTS

AMWAP was secreted from lipopolysaccharide (LPS)-activated microglia and recombinant AMWAP reduced gene transcription of IL6, iNOS, CCL2, CASP11, and TNFα in BV-2 microglia treated with LPS as TLR4 ligand. This effect was replicated with murine embryonic stem cell-derived microglia (ESdM) and primary brain microglia. AMWAP also diminished pro-inflammatory markers in microglia activated with the TLR2 ligand zymosan but had no effects on IL6, iNOS, and CCL2 transcription in cells treated with CpG oligodeoxynucleotides as TLR9 ligand. Microglial uptake of AMWAP effectively inhibited TLR4-dependent NFκB activation by preventing IRAK-1 and IκBα proteolysis. No inhibition of IκBα phosphorylation or ubiquitination and no influence on overall 20S proteasome activity were observed. Functionally, both microglial nitric oxide (NO) secretion and 661W photoreceptor apoptosis were significantly reduced after AMWAP treatment. AMWAP promoted the filopodia formation of microglia and increased the phagocytic uptake of apoptotic 661W photoreceptor cells.

CONCLUSIONS

AMWAP is secreted from reactive microglia and acts in a paracrine fashion to counter-balance TLR2/TLR4-induced reactivity through NFκB inhibition. AMWAP also induces a neuroprotective microglial phenotype with reduced neurotoxicity and increased phagocytosis. We therefore hypothesize that anti-inflammatory whey acidic proteins could have a therapeutic potential in neurodegenerative diseases of the brain and the retina.

Presep: predicting the propensity of a protein being secreted into the supernatant when expressed in Pichia pastoris

Pichia pastoris is commonly used for the production of recombinant proteins due to its preferential secretion of recombinant proteins, resulting in lower production costs and increased yields of target proteins. However, not all recombinant proteins can be successfully secreted in P. pastoris. A computational method that predicts the likelihood of a protein being secreted into the supernatant would be of considerable value; however, to the best of our knowledge, no such tool has yet been developed. We present a machine-learning approach called Presep to assess the likelihood of a recombinant protein being secreted by P. pastoris based on its pseudo amino acid composition (PseAA). Using a 20-fold cross validation, Presep demonstrated a high degree of accuracy, with Matthews correlation coefficient (MCC) and overall accuracy (Q2) scores of 0.78 and 95%, respectively. Computational results were validated experimentally, with six β-galactosidase genes expressed in P. pastoris strain GS115 to verify Presep model predictions. A strong correlation (R(2) = 0.967) was observed between Presep prediction secretion propensity and the experimental secretion percentage. Together, these results demonstrate the ability of the Presep model for predicting the secretion propensity of P. pastoris for a given protein. This model may serve as a valuable tool for determining the utility of P. pastoris as a host organism prior to initiating biological experiments. The Presep prediction tool can be freely downloaded at http://www.mobioinfor.cn/Presep.

Efficient secretion of lipase r27RCL in Pichia pastoris by enhancing the disulfide bond formation pathway in the endoplasmic reticulum

The lipase r27RCL from Rhizopus chinensis CCTCC M201021 was heterologously expressed in Pichia pastoris GS115 by simultaneous co-expression with two secretion factors ERO1p and PDI involved in the endoplasmic reticulum (ER). Compared to the expression of the lipase alone (12,500 U/ml), co-expression with these two proteins resulted in the production of larger total quantities of enzymes. The largest increase was seen when the combined ERO1p/PDI system was co-expressed, resulting in approximately 30 % higher enzyme yields (16,200 U/ml) than in the absence of co-expressed secretion factors. The extracellular protein concentration of the recombinant strain Co XY RCL-5 reached 9.39 g/l in the 7-l fermentor. Simultaneously, the fermentation time was also shortened by about 8 h compared to that of the control. The substrate-specific consumption rate (Qs) and the product-specific production rate (Qp) were both investigated in this research. In conclusion, the space–time yield was improved by co-expression with ERO1p and PDI. This is a potential strategy for high level expression of other heterologous proteins in P. pastoris.

Enhancement of lipase r27RCL production in Pichia pastoris by regulating gene dosage and co-expression with chaperone protein disulfide isomerase

Pichia pastoris has been successfully used in the production of many secreted and intracellular recombinant proteins, but there is still a large room of improvement for this expression system. Two factors drastically influence the lipase r27RCL production from Rhizopus chinensis CCTCC M201021, which are gene dosage and protein folding in the endoplasmic reticulum (ER). Regarding the effect of gene dosage, the enzyme activity for recombinant strain with three copies lipase gene was 1.95-fold higher than that for recombinant strain with only one copy lipase gene. In addition, the lipase production was further improved by co-expression with chaperone PDI involved in the disulfide bond formation in the ER. Overall, the maximum enzyme activity reached 355U/mL by the recombinant strain with one copy chaperone gene PDI plus five copies lipase gene proRCL in shaking flasks, which was 2.74-fold higher than that for the control strain with only one copy lipase gene. Overall, co-expression with PDI vastly increased the capacity for processing proteins of ER in P. pastoris.

Impact of gene dosage on the production of lipase from Rhizopus chinensis CCTCC M201021 in Pichia pastoris

In this work, the high-level expression of the lipase r27RCL was achieved by optimization of the lipase gene copy number in the host strain Pichia pastoris. The copy number of the lipase gene proRCL from Rhizopus chinensis CCTCC M201021 was quantified by real-time quantitative polymerase chain reaction and a range of Mut(+) P. pastoris strains carrying one, three, five, and six copies of proRCL were obtained. The maximum lipase activity was achieved at 12,500 U/mL by the five-copy recombinant strain after 96 h of methanol induction in the 7-L fermenter. However, the enzyme activity of the six-copy recombinant strain decreased remarkably. By transcription analysis of proRCL, ERO1, and PDI, it suggested that unfolded protein response seemed to be triggered in the highest copy recombinant strain after 24 h. Thus, elaborate optimization of foreign gene dosage was very important for the high-level expression of foreign proteins in P. pastoris.

The effect of gene copy number and co-expression of chaperone on production of albumin fusion proteins in Pichia pastoris

Interleukin-1 receptor antagonist (IL1ra) is known to treat a number of diseases such as rheumatoid arthritis and type 2 diabetes. However, the biological half-life of IL1ra is very short due to its rapid renal clearance. Our present study aimed to increase the biological half-life of IL1ra through fusion with human serum albumin (HSA), and then augmented expression of the IL1ra and HSA fusion protein (IH) in Pichia pastoris strain by increasing IH gene copy number or was co-expressed with chaperone. By comparing clones containing varying copy numbers of IH fusion gene, it was observed that higher levels of secretory IH fusion protein was produced in strain with higher IH gene copy number. In addition, IH protein yield was further improved after being co-expressed with protein disulfide isomerase (PDI). Conversely, it was significantly decreased (i.e., secretory IH in the culture medium) by co-expression of immunoglobulin binding protein. We have also discussed whether the multi-copy strain and co-expressed of PDI could enhance the levels of other secretory albumin fusion protein (e.g., HSA and human growth hormone fusion protein). Interestingly, the level of this fusion protein was apparently also increased by these approaches. In conclusion, our results have demonstrated that increasing copy number and co-expression of PDI may raise yield of albumin fusion protein in P. pastoris, which might probably contribute to the industry for the development of proteinous drugs.