Multiple copies of the target gene enhances plectasin secretion in Pichia pastoris X-33

Boosting expression level of plectasin in recombinant Pichia pastoris via 2A self-processing peptide assembly

Plectasin is a promising and potent antimicrobial peptide isolated from the fungus Pseudoplectania nigrella which has been heterologously expressed in various hosts. In this study, a four-copy cassette of plectasin was constructed via 2A peptide assembly to further increase its expression level in recombinant Pichia pastoris. The yeast transformant 4Ple-61 harboring four-copy cassette of plectasin could secrete 183.2 mg/L total protein containing 60.8% of plectasin at the flask level within 120 h, which was 2.3 times higher than that of the yeast transformant Ple-6 carrying one-copy cassette of plectasin. Western blot confirmed the significant peptide expression level in the transformant 4Ple-61. Furthermore, it yielded as high as 426.3 mg/L total protein within 120 h during a 5-L fermentation. The purified plectasin shows superior stability and good antimicrobial activity against conventional Staphylococcus aureus ATCC 26,001 and some food-borne antibiotic-resistant S. aureus strains with the MICs ranging from 8 to 32 μg/mL. Therefore, the strategy based on 2A peptide assembly can enhance the expression of plectasin and further expand its application prospect. KEY POINTS: • A yeast transformant 4Ple-61 with four-copy cassette of plectasin was constructed. • The plectasin level yield by the transformant 4Ple-61 was boosted by 2.3 times. • The plectasin showed good activity against food-borne antibiotic-resistant S. aureus.

High level production of stable human serum albumin in Pichia pastoris and characterization of the recombinant product

Human serum albumin (HSA) is an important therapeutic used in clinical settings for restoration of blood volume and treatment of chemotherapy induced neutropenia. Currently sourced from human serum, it carries the risk of contamination with viruses. The production of stable extracellular recombinant (r)HSA was achieved at nearly 1 g/L at shake-flask level in Pichia pastoris (syn. Komagataella phaffii) containing a three-copy containing HSA expression cassette, prepared in vitro. The HSA specific transcripts were increased by 1.82- to 2.46-fold in the three-copy containing clones indicating increased transcript levels to result in enhanced production of extracellular rHSA. The purified rHSA displayed secondary structure, zeta potential, size distribution and biological efficacy that matched with that of the commercial HSA. Cultivation strategy was developed at bioreactor level for the single HSA expression cassette containing recombinant which led to productivity of 300 mg/L/d of rHSA with minimum proteolytic cleavage.

A multi-functional genetic manipulation system and its use in high-level expression of a β-mannanase mutant with high specific activity in Pichia pastoris

To further extend the practical application of a thermostable and acidic resistance β-mannanase (ManAK) in animal feed additives, an effective strategy that combined directed evolution and metabolic engineering was developed. Four positive mutants (P191M, P194E, S199G and S268Q) with enhanced specific activity (25.5%-60.9%) were obtained. The S199G mutant exhibited 56.7% enhancement of specific activity at 37°C and good thermostability, and this was selected for high-level expression in P. pastoris X33. A multi-functional and scarless genetic manipulation system was proposed and functionally verified (gene deletion, substitution/insertion and point mutation). This was then subjected to Rox1p (an oxygen related transcription regulator) deletion and Vitreoscilla haemoglobin (VHb) co-expression for high enzyme productivity in P. pastoris X33VIIManAKS199G . An excellent strain, named X33VIIManAKS199G ∆rox1::VHb, was achieved by combining these two factors, and then the maximum enzymatic activity was further increased to 3753 U ml-1 , which was nearly twice as much as the maximum production of ManAK in P. pastoris. This work provides a systematic and effective method to improve the enzymatic yield of β-mannanase, promotes the application of ManAK in feed additives, and also demonstrated that a scarless genetic manipulation tool is useful in P. pastoris.

Overexpression of endogenous stress-tolerance related genes in Saccharomyces cerevisiae improved strain robustness and production of heterologous cellobiohydrolase

To enable Saccharomyces cerevisiae to produce renewable fuels from lignocellulose in a consolidated bioprocess, a heterologous cellulase system must be engineered into this yeast. In addition, inherently low secretion titers and sensitivity to adverse environmental conditions must be overcome. Here, two native S. cerevisiae genes related to yeast stress tolerance, YHB1 and SET5, were overexpressed under transcriptional control of the constitutive PGK1 promoter and their effects on heterologous secretion of Talaromyces emersonii cel7A cellobiohydrolase was investigated. Transformants showed increased secreted enzyme activity that ranged from 22% to 55% higher compared to the parental strains and this did not lead to deleterious growth effects. The recombinant strains overexpressing either YHB1 or SET5 also demonstrated multi-tolerant characteristics desirable in bioethanol production, i.e. improved tolerance to osmotic and heat stress. Quantitative reverse transcriptase PCR analysis in these strains showed decreased transcription of secretion pathway genes. However, decreased unfolded protein response was also observed, suggesting novel mechanisms for enhancing enzyme production through stress modulation. Overexpression of YHB1 in an unrelated diploid strain also enhanced stress tolerance and improved ethanol productivity in medium containing acetic acid. To our knowledge, this is the first demonstration that improved heterologous secretion and environmental stress tolerance could be engineered into yeast simultaneously.

A eukaryotic expression strategy for producing the novel antimicrobial peptide PRW4

The antimicrobial peptide PMAP-36 is a cationic peptide derived from porcine myeloid. The N-terminally paired lysine of PMAP-36 was substituted with tryptophan, and the C-terminal hydrophobic tail was deleted, thereby obtaining the antimicrobial peptide PRW4. PRW4 is a α-helical antimicrobial peptide with broad-spectrum antimicrobial activity. In this study, PRW4 was fused to the 6× His-Trx, and the fusion protein was successfully expressed in Pichia pastoris GS115 from the vector pPICZαA. The maximal induction of recombinant protein occurred in the presence of 1% methanol after 96 h at pH 6.0. After purification by a Ni-NTA resin column and digestion by enterokinase protease, 15 mg of recombinant PRW4 with a purity of 90% was obtained from 1 L of fermentation culture. The results indicated that recombinant PRW4 had similar antimicrobial activity as synthetic PRW4 against bacteria such as Escherichia coli ATCC 25922, Escherichia coli UB 1005, Salmonella typhimurium C7731, Salmonella typhimurium 7913, Salmonella typhimurium ATCC 14028, Staphylococcus aureus ATCC 29213, Staphylococcus epidermidis ATCC 12228, and Streptococcus faecalis ATCC 29212. We have successfully expressed PRW4 in P. pastoris, and this work provides a reference for the production of modified antimicrobial peptides in P. pastoris.

Constitutive expression of the active fragment of human vasostatin Vs30 in Pichia pastoris SMD1168H

Vasostatin 30 (Vs30) is an active fragment derived from the N-terminal region (135-164 aa) of human calreticulin and has the ability to inhibit angiogenesis. In this work, the expression of Vs30 was performed using a protease-deficient strain of the methylotrophic yeast Pichia pastoris. The vs30 gene was optimized for P. pastoris preferential codon usage and inserted into constitutive expression vector pGAPZαA. In addition, a plasmid with four copies of the expression cassette was obtained and transformed into P. pastoris. The flask fermentation conditions were: culture volume of 25 mL in 250 mL baffled flasks at 28 °C, pH 6 and harvest time of 48 h. Up to 21.07 mg/L Vs30 were attained and purified by ultrafiltration with a 30-kDa cut-off membrane and the recovery was 49.7%. Bioactivity of Vs30 was confirmed by the inhibition of cell proliferation, as well as the inhibition of the capillary-like structures formation of EA.hy926 cells in vitro. This work constitutes the first report on the expression of Vs30 in Pichia pastoris using a constitutive promoter and multi-copy approach such as strategies to improve the recombinant Vs30 expression.

Methanol-Independent Protein Expression by AOX1 Promoter with trans-Acting Elements Engineering and Glucose-Glycerol-Shift Induction in Pichia pastoris

The alcohol oxidase 1 promoter (P_AOX1) of Pichia pastoris is commonly used for high level expression of recombinant proteins. While the safety risk of methanol and tough process control for methanol induction usually cause problems especially in large-scale fermentation. By testing the functions of trans-acting elements of P_AOX1 and combinatorially engineering of them, we successfully constructed a methanol-free P_AOX1 start-up strain, in which, three transcription repressors were identified and deleted and, one transcription activator were overexpressed. The strain expressed 77% GFP levels in glycerol compared to the wide-type in methanol. Then, insulin precursor (IP) was expressed, taking which as a model, we developed a novel glucose-glycerol-shift induced P_AOX1 start-up for this methanol-free strain. A batch phase with glucose of 40 g/L followed by controlling residual glucose not lower than 20 g/L was compatible for supporting cell growth and suppressing P_AOX1. Then, glycerol induction was started after glucose used up. Accordingly, an optimal bioprocess was further determined, generating a high IP production of 2.46 g/L in a 5-L bioreactor with dramatical decrease of oxygen consumption and heat evolution comparing with the wild-type in methanol. This mutant and bioprocess represent a safe and efficient alternative to the traditional glycerol-repressed/methanol-induced P_AOX1 system.

Genome-wide landscape of position effects on heterogeneous gene expression in Saccharomyces cerevisiae

BACKGROUND

Integration of heterogeneous genes is widely applied in synthetic biology and metabolic engineering. However, knowledge about the effect of integrative position on gene expression remains limited.

RESULTS

We established a genome-wide landscape of position effect on gene expression in Saccharomyces cerevisiae. The expression cassette of red fluorescence protein (RFP) gene was constructed and inserted at 1044 loci, which were scattered uniformly in the yeast genome. Due to the different integrative loci on the genome, the maximum relative intensity of RFP is more than 13-fold over the minimum. Plots of the number of strains to RFP relative intensity showed normal distribution, indicating significant position effect on gene expression in yeast. Furthermore, changing the promoters or reporter genes, as well as carbon sources, revealed little consequences on reporter gene expression, indicating chromosomal location is the major determinant of reporter gene expression.

CONCLUSIONS

We have examined the position effects to integration genes expression in large number loci around whole genome in S. cerevisiae. The results could guide the design of integration loci for exogenous genes and pathways to maximize their expression in metabolic engineering.

RSM optimization of HSA/IL1Ra in Pichia pastoris overexpression strain and study of its in vivo activity in reducing hyperglycemia of GK rats

Human serum albumin (HSA) and interleukin-1 receptor antagonist (IL1Ra) fusion protein is a potential long-acting drug in the treatment of type 2 diabetes. Previously, the expression level of HSA/IL1Ra in Pichia pastoris was successfully improved by increasing the gene copy number and coexpression with chaperone (protein disulfide isomerase) in our laboratory. However, the overexpression strain resulted in low production of high- cell-density fermentation. In this study, the culture medium was optimized in both flask and fermenter, and the optimum culture medium notably increased the productivity and stability of HSA/IL1Ra. To further improve the expression, response surface methodology was used to further optimize the culture condition through modeling three selected parameters (induction pH, induction temperature [T], and maximum methanol feed rate [V_m ]). The maximum yield of HSA/IL1Ra reached 1.1 g/L (10-fold higher than original fermentation condition) under the optimized culture condition (pH 7.0, T = 29 ℃ and V_m = 4.82 mL/L/H) in a 5-L fermenter. In addition, the degradation position of HSA/IL1Ra during fermentation was determined to be K571, serving as a potential target for genetic modification strategies to reduce the degradation. Finally, the in vivo activity study showed that HSA/IL1Ra maintained the therapeutic effect of IL1Ra in type 2 diabetes model rats meanwhile reducing the frequency of administration.

Enhanced secretion of a methyl parathion hydrolase in Pichia pastoris using a combinational strategy

BACKGROUND

Although Pichia pastoris has been successfully used to produce various recombinant heterologous proteins, the efficiency varies. In this study, we used methyl parathion hydrolase (MPH) from Ochrobactrum sp. M231 as an example to study the effect of protein amino acid sequence on secretion from P. pastoris.

RESULTS

The results indicated that the protein N-terminal sequence, the endoplasmic reticulum (ER) retention signal (KKXX) at the protein C-terminus, and the acidic stability of the protein could affect its secretion from P. pastoris. Mutations designed based on these sequence features markedly improved secretion from P. pastoris. In addition, we found that the secretion properties of a protein can be cumulative when all of the above strategies are combined. The final mutant (CHBD-DQR) designed by combining all of the strategies greatly improved secretion and the secreted MPH activity of CHBD-DQR was enhanced up to 195-fold compared with wild-type MPH without loss of catalytic efficiency.

CONCLUSIONS

These results demonstrate that the secretion of heterologous proteins from P. pastoris could be improved by combining changes in multiple protein sequence features.