Constitutive Expression of a rhIL-2-HSA Fusion Protein in Pichia pastoris Using Glucose as Carbon Source

Medium optimization for high yield production of human serum albumin in Pichia pastoris and its efficient purification

OBJECTIVE

To improve the yield of recombinant human serum albumin (HSA) in Pichia pastoris by medium optimization and establish the related purification scheme.

RESULTS

A simplified version of the generally used buffered glycerol complex medium (BMGY), which contained yeast extract, glycerol and potassium salts, was found to be applicable. By decreasing the salt concentration of basal salt medium (BSM) to half of the original formula further, we achieved a high yield of 17.47 g/L HSA in the supernatant within a 192 h induction, which is the highest rHSA yield ever reported as far as we know. Accompanied with a three-step purification procedure which recovered two thirds of the desired protein at high purity, our work lays a solid foundation for large-scale industrial production of HSA.

CONCLUSION

Medium optimization plays a significant role in improving the yield of desired protein, lowering the production cost and helping to explore the producing strain's character.

Bioengineered Human Serum Albumin Fusion Protein as Target/Enzyme/pH Three-Stage Propulsive Drug Vehicle for Tumor Therapy

Human serum albumin (HSA) has the characteristics of biocompatibility and long circulation, which is widely used as the carrier of insoluble anticancer drugs, but it also has some disadvantages such as weak tumor targeting and uncontrollable drug release. Herein, HSA was modified to improve its biological performance by introducing polyhistidine (pHis), matrix metalloproteinase-2 (MMP-2) digestion, and Arg-Gly-Asp (RGD) peptide at the separated end of HSA through gene fusion technology. The resulting protein expressed by Pichia pastoris could self-assemble into 3RGD-HSA-MMP-18His nanoparticles (RHMH18 NPs) accompanied by loading hydrophobic drug paclitaxel (PTX) into the polyhistidine micelle core. RHMH18 NPs exhibited active tumor targeting in high efficiency owing to the RGD-mediated specific binding toward α_νβ₃-integrin upregulated on tumor vasculature endothelium, resulting in the enrichment of therapeutic substances in tumor sites. Once reaching the tumor microenvironment, RHMH18 NPs was cut off by MMP-2 to remove the HSA-3RGD moiety, leaving the small and positively charged histidine micelle, which could penetrate the deep part of tumor tissue more effectively. Finally, the histidine micelle escaped from lysosome successfully and released drug in response to pH. The in vivo experiments' results demonstrated that the three-stage propulsion RHMH18 NPs presented superior tumor inhibition activity with minimal side effects, providing potential strategies of protein based drug delivery systems for tumor therapy.

Expression and characterization of albumin fusion protein canine IFNγ-CSA in baculovirus-insect cell expression system

In this study, canine IFNγ was fused by a flexible linker with canine serum albumin to construct the fusion protein IFNγ-CSA for the purpose to design a long-acting canine IFNγ. The fusion protein was successfully expressed in baculovirus-infected Sf9 insect cells and was purified by salting-out and ion exchange chromatography. The IFNγ-CSA fusion possessed potent anti-viral assay against vesicular stomatitis virus in cultured cells. IFNγ-CSA was also stable at 37 °C up to 72 h compared with 8 h for IFNγ alone. In vivo pharmacokinetics demonstrated a significantly longer half-life for IFNγ-CSA (15.42 h) than for canine reIFNγ (1.51 h) in KM mice. These results indicate that IFNγ-CSA expression in the baculovirus system was successful and provide a promising long-acting cytokine for veterinary clinical applications.

An efficient constitutive expression system for Anti-CEACAM5 nanobody production in the yeast Pichia pastoris

Nanobodies offer multiple advantages over conventional antibodies in terms of size, stability, solubility, immunogenicity, and production costs, with improved tumor uptake and blood clearance. Additionally, the recombinant expression of nanobodies is robust in various expression systems, such as Escherichia coli, Saccharomyces cerevisiae and Pichia pastoris. P. pastoris is the most widely used microorganism for nanobody production, but all or almost all expression vectors developed for this system are based on the regulated promoter of the alcohol oxidase 1 gene (AOX1) that requires methanol for full induction. In this study, a constitutive anti-CEACAM5 nanobody expression system was constructed under the control of a glyceraldehyde-3-phosphate dehydrogenase promoter (GAP) promoter. The effects of different carbon sources and pH on nanobody expression were evaluated in shaking flask cultures. After 96 h of constitutive expression in shaking flask, a yield of 51.71 mg/L was obtained. In addition, this constitutive expression system produced nanobodies at equivalent yield and affinity to that produced by methanol-induced expression. The results of this study indicated that the use of a constitutive expression system is a promising alternative for the production of nanobodies applied for cancer diagnosis and therapy.

Carbon metabolism influenced for promoters and temperature used in the heterologous protein production using Pichia pastoris yeast

Nowadays, it is necessary to search for different high-scale production strategies to produce recombinant proteins of economic interest. Only a few microorganisms are industrially relevant for recombinant protein production: methylotrophic yeasts are known to use methanol efficiently as the sole carbon and energy source. Pichia pastoris is a methylotrophic yeast characterized as being an economical, fast and effective system for heterologous protein expression. Many factors can affect both the product and the production, including the promoter, carbon source, pH, production volume, temperature, and many others; but to control all of them most of the time is difficult and this depends on the initial selection of each variable. Therefore, this review focuses on the selection of the best promoter in the recombination process, considering different inductors, and the temperature as a culture medium variable in methylotrophic Pichia pastoris yeast. The goal is to understand the effects associated with different factors that influence its cell metabolism and to reach the construction of an expression system that fulfills the requirements of the yeast, presenting an optimal growth and development in batch, fed-batch or continuous cultures, and at the same time improve its yield in heterologous protein production.

Heterologous expression of the human polybromo-1 protein in the methylotrophic yeast Pichia pastoris

The human polybromo-1 protein (BAF180) is a known driver mutation in clear cell renal cell carcinoma, where it is mutated in approximately 40% of cases. BAF180 is the chromatin-targeting subunit of the PBAF complex. BAF180 has six bromodomains, two BAH domains, and one HMG box. Bromodomains are known to recognize acetylated-lysines on histones and play a role in nucleosome recognition. BAH domains are required for ubiquitination of PCNA, a key regulator of DNA damage. The putative HMG box, if functional, may be involved in DNA-binding. While the binding specificities of individual bromodomains have been studied by our lab and others, the results have failed to reach a consensus. The acetyl-histone binding features of the full-length protein is unknown and is the motivation for this work. The hypothetical HMG and BAH domains have not been studied and the actual function of these regions is currently unknown. Thus, the precise interactions of this large and complex protein are not well-studied. Advances in understanding this large protein have been hindered by the inability to express and purify recombinant full-length BAF180 protein. Currently, only phenomenological studies using BAF180 expressed in mammalian cells have been conducted. Here, we report the successful expression, purification of full-length biologically active BAF180 protein using the GAP promoter in the heterologous host Pichia pastoris. The ability to express full-length and mutated BAF180 will allow for biophysical binding studies. Knowledge of the binding interactions is critical for us to understand the role of BAF180 in cancer development and its progression.

Effects of co-overexpression of secretion helper factors on the secretion of a HSA fusion protein (IL2-HSA) in pichia pastoris

Pichia pastoris is generally considered as an expression host for heterologous proteins with the coding gene under control of the alcohol oxidase 1 (AOX1) promoter. The secretion of heterologous proteins in P. pastoris can be potentially affected by many factors. Based on our previous results, the secretion levels of human albumin (HSA) fusion protein IL2-HSA were only around 500 mg/L or less in fermentor cultures, which decreased more than 50% compared with that of HSA (>1 g/L). In this study, we selected five potential secretion helper factors, in which Ero1, Pdi1 and Kar2 were involved in protein folding and Sec1 and Sly1 were involved in vesicle trafficking. We evaluated the possible effects of individual overexpression of these secretion helper factors on the secretion of IL2-HSA in P. pastoris. Constitutive overexpression of the five selected secretion factors did not have an obvious negative effect on cell growth of the IL2-HSA secreting strain. Individual co-overexpression of Ero1, Kar2, Pdi1, Sec1 and Sly1 improved the secretion level of IL2-HSA to ~2.3-, 1.9-, 2.2-, 2.5- and 1.9-fold that in the control strain respectively in shake flasks. We evaluated the changes in mRNA and protein levels of the intracellular IL2-HSA, as well as the secretion helper factor genes in the co-overexpressing strains. Our results indicated that manipulating the expression level of ER resident protein Pdi1, Ero1, Kar2 and SM protein Sec1 and Sly1 could improve the secretion level of IL2-HSA fusion protein in P. pastoris, which provided new candidates for combinatorial engineering in future study. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of inducible versus constitutive expression of plectasin on yields and antimicrobial activities in Pichia pastoris

BACKGROUND

Plectasin might serve as a substitute for traditional antibiotics, but its yields and antimicrobial activities warrant further investigation.

OBJECTIVE

To identify the influence of inducible versus constitutive expression of plectasin on yields and antimicrobial activities.

METHODS

Through SOE-PCR, a recombinant plectasin gene was generated and inserted into inducible (pPICZαA) and constitutive (pGAPZαA) vectors in order to create Pichia pastoris GS115 strains. After 120 h of fermentation, supernatants were purified by an AKTA purifier using nickel columns. Minimal inhibitory concentration (MIC) and inhibition zone assays were performed after Tricine-SDS-PAGE.

RESULTS

After 120 h of fermentation, the yield of constitutive plectasin (370 μg/ml) was much lower than that from inducible vector (880 μg/ml) (P < 0.05). However, constitutive strain reached its plateau phase faster and keep more consistent yield (P < 0.05). The MICs of inducible plectasin against Methicillin-resistant Staphylococcus aureus (MRSA) 15471118, vancomycin-resistant Enterococcus feces (VREF), and penicillin-resistant Streptococcus pneumonia (PRSP) 31355 were 64, 32, and 64 μg/ml, respectively, while those of constitutive plectasin were 4, 4, and 16 μg/ml. No significant differences were observed in antimicrobial activities between inducible and constitutive plectasin for MRSA 15471118, VREF and PRSP 31355 (all P ＞ 0.05). However, constitutive plectasin had a larger inhibition zone than inducible plectasin with the same mass.

CONCLUSIONS

Although P. pastoris GS115 (pGAPZαA-Plectasin-GS115) had lower expression than P. pastoris GS115 (pPICZαA-plectasin-GS115), it reached the plateau phase faster, had steadier yields and showed superiority in antimicrobial activities. Therefore, pGAPZαA might be more suitable for expression of plectasin in GS115 compared with pPICZαA.

An Efficient Genome-Wide Fusion Partner Screening System for Secretion of Recombinant Proteins in Yeast

To produce rarely secreted recombinant proteins in the yeast Saccharomyces cerevisiae, we developed a novel genome-wide optimal translational fusion partner (TFP) screening system that involves recruitment of an optimal secretion signal and fusion partner. A TFP library was constructed from a genomic and truncated cDNA library by using the invertase-based signal sequence trap technique. The efficiency of the system was demonstrated using two rarely secreted proteins, human interleukin (hIL)-2 and hIL-32. Optimal TFPs for secretion of hIL-2 and hIL-32 were easily selected, yielding secretion of these proteins up to hundreds of mg/L. Moreover, numerous uncovered yeast secretion signals and fusion partners were identified, leading to efficient secretion of various recombinant proteins. Selected TFPs were found to be useful for the hypersecretion of other recombinant proteins at yields of up to several g/L. This screening technique could provide new methods for the production of various types of difficult-to-express proteins.

Can too many copies spoil the broth?

The success of Pichia pastoris as a heterologous expression system lies predominantly in the impressive yields that can be achieved due to high volumetric productivity. However, low specific productivity still inhibits the potential success of this platform. Multi-(gene) copy clones are potentially a quick and convenient method to increase recombinant protein titer, yet they are not without their pitfalls. It has been more than twenty years since the first reported use of multi-copy clones and it is still an active area of research to find the fastest and most efficient method for generating these strains. It has also become apparent that there is not always a linear correlation between copy number and protein titer, leading to in-depth investigations into how to minimize the negative impact of secretory stress and achieve clonal stability.