Causes of proteolytic degradation of secreted recombinant proteins produced in methylotrophic yeastPichia pastoris: Case study with recombinant ovine interferon-?

Fed-batch methanol feeding strategy for recombinant protein production by Pichia pastoris in the presence of co-substrate sorbitol

Batch-wise sorbitol addition as a co-substrate at the induction phase of methanol fed-batch fermentation by Pichia pastoris (Mut(+)) was proposed as a beneficial recombinant protein production strategy and the metabolic responses to methanol feeding rate in the presence of sorbitol was systematically investigated. Adding sorbitol batch-wise to the medium provided the following advantages over growth on methanol alone: (a) eliminating the long lag-phase for the cells and reaching 'high cell density production' at t = 24 h of the process (C(X) = 70 g CDW/l); (b) achieving 1.8-fold higher recombinant human erythropoietin (rHuEPO) (at t = 18 h); (c) reducing specific protease production 1.2-fold; (d) eliminating the lactic acid build-up period; (e) lowering the oxygen uptake rate two-fold; and (f) obtaining 1.4-fold higher overall yield coefficients. The maximum specific alcohol oxidase activity was not affected in the presence of sorbitol, and it was observed that sorbitol and methanol were utilized simultaneously. Thus, in the presence of sorbitol, 130 mg/l rHuEPO was produced at t = 24 h, compared to 80 mg/l rHuEPO (t = 24 h) on methanol alone. This work demonstrates not only the ease and efficiency of incorporating sorbitol to fermentations by Mut(+) strains of P. pastoris for the production of any bio-product, but also provides new insights into the metabolism of the methylotrophic yeast P. pastoris.

Secreted production of an elastin-like polypeptide by Pichia pastoris

Elastin-like polypeptides (ELPs) are biocompatible designer polypeptides with inverse temperature transition behavior in solution. They have a wide variety of possible applications and a potential medical importance. Currently, production of ELPs is done at lab scale in Escherichia coli shake flask cultures. With a view to future large scale production, we demonstrate secreted production of ELPs in methanol-induced fed-batch cultures of Pichia pastoris and purification directly from the culture medium. The production of ELPs by P. pastoris proved to be pH dependent within the experimental pH range of pH 3 to 7, as an increasing yield was found in cultures grown at higher pH. Because ELP produced at pH 7 was partly degraded, a pH optimum for production of ELP was found at pH 6 with a yield of 255 mg of purified intact ELP per liter of cell-free medium.

Enhancement of alkaline polygalacturonate lyase production in recombinant Pichia pastoris according to the ratio of methanol to cell concentration

Polygalacturonate lyase (PGL) production by Pichia pastoris GS115 was used as a model to study the mechanism and strategy for enhancing heterologous protein production. It was found that the ratio of methanol to cell concentration had a significant influence on PGL production. In this study, an advanced glycerol exponential feeding strategy was developed for biomass accumulation in cell growth phase, by which cell concentration reached 140 g L(-1) after 19 h glycerol feeding. In subsequent production phase, a methanol feeding profile was proposed according to the optimal ratio of methanol to cell concentration at a range of 0.163-0.171 g g(-1), and PGL activity and productivity reached 430 U mL(-1) and 4.34 U mL(-1)h(-1), respectively. The strategy for enhancing PGL production by controlling the optimal ratio may provide an alternative approach to enhance heterologous protein production with P. pastoris.

Inhibition of degradation and aggregation of recombinant human consensus interferon-alpha mutant expressed in Pichia pastoris with complex medium in bioreactor

The methylotrophic yeast Pichia pastoris has been used for the expression of many proteins. However, limitations such as protein degradation and aggregation became obvious when secreting heterologous protein-recombinant human consensus interferon-alpha mutant. Here, we investigate the effect of induction temperature on the yield and stability of interferon mutant expressed by P. patoris with buffered complex medium. The best results in terms of interferon mutant bioactivity and specific bioactivity were obtained when the microorganism was induced at 15 degrees C, which were 2.91 x 10(8) +/- 0.3 x 10(8) and 2.26 x 10(8 )+/- 0.23 x 10(8) IU mg(-1), respectively. At the same time, the cells grew fast owing to high AOX1-specific activity, and interferon mutant expression level reached 1.23 g l(-1), which was almost 30 times higher than that in the flask. Also, the proteolytic degradation of interferon mutant was inhibited completely because of lower protease bioactivity probably due to a reduced cell death rate at lower temperatures as well as protection of yeast extract and peptone in complex medium. In addition, interferon mutant aggregation was repressed significantly by the addition of Tween-80, and a specific bioactivity of 7.35 x 10(8) +/- 0.56 x 10(8) IU mg(-1) was obtained. These results should be applicable to other low-stability recombinant proteins expressed in P. pastoris.

Improving intracellular production of recombinant protein in Pichia pastoris using an optimized preinduction glycerol-feeding scheme

High-cell-density production of recombinant growth hormone of Lateolabrax japonicus (rljGH) expressed intracellularly in Pichia pastoris was investigated. In the regular strategy of induction at a cell density of 160 g l(-1), short duration of intracellular rljGH accumulation (17 h) resulted in a low final cell density of 226 g l(-1). Thus, a novel strategy of induction at a cell density of 320 g l(-1) was investigated. In this strategy, the preinduction glycerol-feeding scheme had a significant effect on the post-induction production. Constant glycerol feeding led to a decrease of the specific rljGH production and specific production rate because of low preinduction specific growth rate. This decrease was avoided by exponential glycerol feeding to maintain a preinduction specific growth rate of 0.16 h(-1). The results from exponential glycerol feeding indicated that the rljGH production depended on the preinduction specific growth rate. Moreover, mixed feeding of methanol and glycerol during induction improved the specific production rate to 0.07 mg g(-1) h(-1) from 0.043 mg g(-1) h(-1). Consequently, both high cell density (428 g l(-1)) and high rljGH production could be achieved by the novel strategy: growing the cells at the specific growth rate of 0.16 h(-1) to the cell density of 320 g l(-1) and inducing the expression by mixed feeding.

Changing the N-terminal sequence protects recombinant Plasmodium falciparum circumsporozoite protein from degradation in Pichia pastoris

Proteolytic degradation is the primary obstacle in the use of the yeast Pichia pastoris for the expression of recombinant proteins. During the production of a recombinant Plasmodium falciparum circumsporozoite protein in this system, the (NANP)( n ) repeats region at the N-terminus were completely proteolytically degraded. To remove the potential proteolytic site within the recombinant protein, different strategies were tried, including adjusting the cultivation conditions and mutating the sequence at the junction of the repeat domain and C-terminal region, but the degradation continued. However, modification of the N-terminal sequence by adding an epitope-based peptide to the N-terminus not only protected the repeat domain from cleavage by native proteases during longer induction in the yeast host and purification process, but also stabilized this recombinant protein emulsified with adjuvant ISA720 for at least 6 months. The results showed that proteolytic degradation of the recombinant circumsporozoite protein produced in P. pastoris was amino acid sequence (NANP)-specific, and that this effect was likely dependent on the conformation of the recombinant protein.

Purification of the N- and C-terminal subdomains of recombinant heavy chain fragment C of botulinum neurotoxin serotype C

The N-terminal and C-terminal portions of the heavy chain fragment C from botulinum neurotoxin serotype C [rBoNT(HC)] were expressed in Pichia pastoris and purified by ion-exchange chromotography (IEC). The N-terminal fragment, rBoNTC(Hc)-N, was purified in three IEC steps: a Q Sepharose Fast Flow (FF) capture step followed by a negative SP Sepharose FF step, and finally, Q Sepharose FF as a polishing step. The purification process resulted in greater than 90% pure rBoNTC(Hc)-N based on SDS-PAGE, and yielded up to 1.02 g of rBoNTC(Hc)-N/kg of cells. Alternately, the C-terminal fragment, rBoNTC(Hc)-C, was purified by using a SP Sepharose FF capture step followed by a second SP Sepharose FF step, and finally a Q Sepharose FF as a polishing step. This purification process resulted in greater than 95% pure rBoNTC(Hc)-C based on SDS-PAGE, and yielded up to 0.2 g of rBoNTC(Hc)-C/kg cells. The final protein yield is a function of protein expression level during fermentation and the purification methods, and usually final protein yield between 0.1 and 2 mg/g cells is acceptable. Another concern is protein degradation. Especially with Pichia, protease activity during cell lysis and purification is always an issue. The importance of N-terminal degradation depends on product and its function. N-terminal sequencing revealed that the purified rBoNTC(Hc)-N is missing the first eight amino acids of the N-terminus of the protein, whereas the purified rBoNTC(Hc)-C protein is intact. After a mouse bioassay test, both the intact rBoNTC(Hc)-C and the rBoNTC(Hc)-N missing the first eight amino acids of the N-terminus have vaccine potency; consequently, partial degradation did not have an impact on these protein's utility.

Effects of pH and temperature on recombinant manganese peroxidase production and stability

The enzyme manganese peroxidase (MnP) is produced by numerous white-rot fungi to overcome biomass recalcitrance caused by lignin. MnP acts directly on lignin and increases access of the woody structure to synergistic wood-degrading enzymes such as cellulases and xylanases. Recombinant MnP (rMnP) can be produced in the yeast Pichia pastoris alphaMnP1-1 in fed-batch fermentations. The effects of pH and temperature on recombinant manganese peroxidase (rMnP) production by P. pastoris alphaMnP1-1 were investigated in shake flask and fed-batch fermentations. The optimum pH and temperature for a standardized fed-batch fermentation process for rMnP production in P. pastoris alphaMnP1-1 were determined to be pH 6 and 30 degrees C, respectively. P. pastoris alphaMnP1-1 constitutively expresses the manganese peroxidase (mnp1) complementary DNA from Phanerochaete chrysosporium, and the rMnP has similar kinetic characteristics and pH activity and stability ranges as the wild-type MnP (wtMnP). Cultivation of P. chrysosporium mycelia in stationary flasks for production of heme peroxidases is commonly conducted at low pH (pH 4.2). However, shake flask and fed-batch fermentation experiments with P. pastoris alphaMnP1-1 demonstrated that rMnP production is highest at pH 6, with rMnP concentrations in the medium declining rapidly at pH less than 5.5, although cell growth rates were similar from pH 4-7. Investigations of the cause of low rMnP production at low pH were consistent with the hypothesis that intracellular proteases are released from dead and lysed yeast cells during the fermentation that are active against rMnP at pH less than 5.5.

Production of recombinant protein in Pichia pastoris by fermentation

This protocol is applicable to recombinant protein expression by small-scale fermentation using the Pichia pastoris expression system. P. pastoris has the capacity to produce large quantities of protein with eukaryotic processing. Expression is controlled by a methanol-inducible promoter, which allows a biomass-generation phase before protein production is initiated. The target protein is secreted directly into a protein-free mineral salt medium, and is relatively easy to purify. The protocol is readily interfaced with expanded bed adsorption for immediate capture and purification of recombinant protein. The setting up of the bioreactor plus the fermentation itself takes 1 wk. Making the master and user seed lots takes approximately 2 wk for each individual clone.

Expression, purification, and characterization of recombinant human keratinocyte growth factor-2 in Pichia pastoris

Keratinocyte growth factor-2 (KGF-2) is a member of the fibroblast growth factor family. The full-length human KGF-2 coding sequence, gained by synthesizing, was cloned into the pPICZalphaA vector in frame with the yeast alpha-factor secretion signal under the transcriptional control of the AOX promoter and integrated into Pichia pastoris strain GS115. In shake-flask culture induced with methanol, the rhKGF-2 content was about 17.5% of the total secreted proteins. Under the optimal conditions, stable production of rhKGF-2 around 1.0g/l was achieved. The recombinant protein was purified by heparin affinity chromatography. A preliminary biochemical characterization of purified rhKGF-2 was performed both by Western blot analysis and biological activity analysis, and the result demonstrated that the recombinant KGF-2 was expressed successfully.

Production of a Rhizopus oryzae lipase from Pichia pastoris using alternative operational strategies

Different cultivation strategies have been compared for the production of Rhizopus oryzae lipase (ROL) from Pichia pastoris. Several drawbacks have been found using a methanol non-limited fed-batch. On the one hand, oxygen limitation appeared at early cell dry weights and, on the other hand, high cell death was observed. A temperature limited fed-batch has been proposed to solve both problems. However, in our case study a methanol non-limited fed-batch results in better productivities. Finally, a lower salt medium were used to overcome cell death problems and a temperature limited fed-batch was applied thereafter to solve oxygen transfer limitations. This combined strategy has resulted in lower productivities when compared to a methanol non-limited fed-batch. However the culture could be longer prolonged and a 1.3-fold purer final product was obtained mainly due to cell death reduction.

Expression of the Trichoderma reesei tyrosinase 2 in Pichia pastoris: isotopic labeling and physicochemical characterization

Trichoderma reesei tyrosinase TYR2 has been demonstrated to be able to oxidize various phenolic compounds and also peptide and protein bound tyrosine, and thus is of great interest for different biotechnological applications. In order to understand the reaction mechanism of the enzyme it would be essential to solve its three dimensional structure. Pichia pastoris is a suitable expression system for the production of recombinant enzymes for NMR studies and therefore we expressed TYR2 in this host. As a result of extensive optimization, the production yield of active histidine tagged tyrosinase purified from P. pastoris shake flask cultures was increased from 2.5 to 24 mg/L. Correct copper concentration in the growth medium was critical for the expression of this copper containing enzyme. Our analysis showed that TYR2 expressed in P. pastoris is post-translationally modified; the C-terminal domain of 153 amino acids of the protein is proteolytically cleaved off from the catalytic domain and the only potential N-glycosylation site is glycosylated. The activities of TYR2 expressed in P. pastoris and T. reesei on diphenolic L-dopa and monophenolic L-tyrosine were rather similar. The TYR2 expressed in P. pastoris showed the same physicochemical properties in CD and unfolding assays as the native TYR2 enzyme. Uniform isotopic (15)N-labeling of TYR2 was carried out with (15)NH(4)SO(4) in minimal medium to assess the suitability of the expression system for investigation by NMR spectroscopy.

Cell bank characterization and fermentation optimization for production of recombinant heavy chain C-terminal fragment of botulinum neurotoxin serotype E (rBoNTE(Hc): Antigen E) by Pichia pastoris

A process was developed for production of a candidate vaccine antigen, recombinant C-terminal heavy chain fragment of the botulinum neurotoxin serotype E, rBoNTE(H(c)) in Pichia pastoris. P. pastoris strain GS115 was transformed with the rBoNTE(H(c)) gene inserted into pHILD4 Escherichia coli-P. pastoris shuttle plasmid. The clone was characterized for genetic stability, copy number, and BoNTE(H(c)) sequence. Expression of rBoNTE(H(c)) from the Mut(+) HIS4 clone was confirmed in the shake-flask, prior to developing a fed-batch fermentation process at 5 and 19 L scale. The fermentation process consists of a glycerol growth phase in batch and fed-batch mode using a defined medium followed by a glycerol/methanol transition phase for adaptation to growth on methanol and a methanol induction phase resulting in the production of rBoNTE(H(c)). Specific growth rate, ratio of growth to induction phase, and time of induction were critical for optimal rBoNTE(H(c)) production and minimal proteolytic degradation. A computer-controlled exponential growth model was used for process automation and off-gas analysis was used for process monitoring. The optimized process had an induction time of 9 h on methanol and produced up to 3 mg of rBoNTE(H(c)) per gram wet cell mass as determined by HPLC and Western blot analysis.

The inhibition of aggregation of recombinant human consensus interferon-alpha mutant during Pichia pastoris fermentation

Lower induction temperature and polyoxyethylene sorbitan monolaurate (Tween-20) were successfully used to inhibit the aggregation of recombinant human consensus interferon-alpha mutant (cIFN) during Pichia pastoris fermentation. When the induction temperature was decreased from 30 to 20 degrees C, the cIFN secreted into the medium was in the form of monomers instead of aggregates. The maximum specific activity at 20 degrees C was 4.04 times as high as that at 30 degrees C. There was no obvious effect on the cell growth at 20 degrees C, but the total protein level was decreased. Similar inhibition effect on cIFN aggregation was observed when 0.2 g l(-1) Tween-20 was added during induction. Furthermore, there was a synergistic effect found between induction temperature and Tween-20 on the inhibition of cIFN aggregation. The maximum specific activity with Tween-20 at 20 degrees C was 19.9-fold higher than that without Tween-20 at 30 degrees C.

Expanded-bed adsorption immobilized-metal affinity chromatography

The protocol describes a method for capture of secreted hexahistidine-tagged proteins using expanded-bed adsorption immobilized-metal affinity chromatography. The starting material for the procedure is any crude feedstock that contains a histidine (His)-tagged target protein. The protocol is exemplified using unclarified broth from Pichia pastoris fermentation as feedstock. The protocol can be used for laboratory studies or as part of a process for production of recombinant biotherapeutics to standards of good manufacturing practice. It takes approximately 5 h to purify proteins from 10 liters of feedstock and a further 5-6 h to sterilize and regenerate the column.

Improvement of cell viability and hirudin production by ascorbic acid in Pichia pastoris fermentation

In recombinant Pichia pastoris fermentation for hirudin production, copious cells were not viable and most of the secreted hirudin molecules were C-terminally truncated at the end of fermentation. In this work, the influences of reactive oxygen species (ROS) on cell viability and hirudin production were subsequently studied. In contrast to the untreated control condition, the addition of ascorbic acid at the methanol fed-batch phase could obviously relieve the damage of intracellular ROS to cell membranes. As a result, the cell viability could be increased to 91% from 74% in control at the end of fermentation and the extracellular proteolysis of hirudin reduced. Intact and total hirudin production, by supplying ascorbic acid, could reach 2.90 and 5.03 g/l, respectively, in contrast to 1.75 and 4.70 g/l at the control condition. Ascorbic acid, 4 mmol/l or more, in the fermentation broth increased markedly the production of the intact hirudin, despite a little effect on total hirudin production.

Pichia pastoris fermentation optimization: energy state and testing a growth-associated model

A growth-associated model was applied to the production of recombinant ovine interferon-tau (rOvIFN-tau) with Pichia pastoris for the purpose of manufacturing preclinical and clinical active material. This model predicts that product yields will be the greatest when the specific growth of the culture is maintained at a steady and optimal rate. However, rOvIFN-tau yields did not meet the expected linear model but most closely corresponded to a polynomial relationship. After transitioning from glycerol to methanol, product accumulated for 31-45 h, and then the yield decreased. This production shift, which has been termed decoupling, was clearly related to time on methanol and not culture density. It was determined that a correlation exists between the decoupling point and a drop in energy state of the cell when expressing beta-galactosidase. By assigning decoupling as a constraint that limits productivity and by reformulating the growth medium, the time prior to decoupling increased to 46.8+/-2.4 h, product yield improved for rOvIFN-tau from 203 to 337 mg l(-1), and the coefficient of variation for yield decreased from 67.9 to 23.3%. A robust and stable fermentation process was realized, resulting in a 210% improvement in total yield from 557+/-357 to 1,172+/-388 mg.

Manufacturing of recombinant therapeutic proteins in microbial systems

Recombinant therapeutic proteins have gained enormous importance for clinical applications. The first recombinant products have been produced in E. coli more than 20 years ago. Although with the advent of antibody-based therapeutics mammalian expression systems have experienced a major boost, microbial expression systems continue to be widely used in industry. Their intrinsic advantages, such as rapid growth, high yields and ease of manipulation, make them the premier choice for expression of non-glycosylated peptides and proteins. Innovative product classes such as antibody fragments or alternative binding molecules will further expand the use of microbial systems. Even more, novel, engineered production hosts and integrated technology platforms hold enormous potential for future applications. This review summarizes current applications and trends for development, production and analytical characterization of recombinant therapeutic proteins in microbial systems.