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

Optimization of expression conditions for a novel NZ2114-derived antimicrobial peptide-MP1102 under the control of the GAP promoter in Pichia pastoris X-33

Background

The infections caused by antibiotic multidrug-resistant bacteria seriously threaten human health. To prevent and cure the infections caused by multidrug-resistant bacteria, new antimicrobial agents are required. Antimicrobial peptides are ideal therapy candidates for antibiotic-resistant pathogens. However, due to high production costs, novel methods of large-scale production are urgently needed.

Results

The novel plectasin-derived antimicrobial peptide-MP1102 gene was constitutively expressed under the control of the GAP promoter. The optimum carbon source and concentration were determined, and 4% glucose (w/v) was initially selected as the best carbon source. Six media were assayed for the improved yield of recombinant MP1102 (rMP1102). The total protein and rMP1102 yield was 100.06 mg/l and 42.83 mg/l, which was accomplished via the use of medium number 1. The peptone and yeast extract from Hongrun Baoshun (HRBS, crude industrial grade, Beijing, China) more effectively improved the total protein and the yield of rMP1102 to 280.41 mg/l and 120.57 mg/l compared to 190.26 mg/l and 78.01 mg/l that resulted from Oxoid (used in the research). Furthermore, we observed that the total protein, antimicrobial activity and rMP1102 yield from the fermentation supernatant increased from 807.42 mg/l, 384,000 AU/ml, and 367.59 mg/l, respectively, in pH5.0 to 1213.64 mg/l, 153,600 AU/ml and 538.17 mg/ml, respectively in pH 6.5 in a 5-l fermenter. Accordingly, the productivity increased from 104464 AU/mg rMP1102 in pH 5.0 to a maximum of 285412 AU/mg rMP1102 in pH 6.5. Finally, the recombinant MP1102 was purified with a cation-exchange column with a yield of 376.89 mg/l, 96.8% purity, and a molecular weight of 4382.9 Da, which was consistent with its theoretical value of 4383 Da.

Conclusions

It’s the highest level of antimicrobial peptides expressed in Pichia pastoris using GAP promoter so far. These results provide an economical method for the high-level production of rMP1102 under the control of the GAP promoter.

High-cell-density fermentation and pilot-scale biocatalytic studies of an engineered yeast expressing the heterologous glycoside hydrolase of 7-β-xylosyltaxanes

The glycoside hydrolase of 7-β-xylosyltaxanes (designated as LXYL-P1-2) is encoded by Lxyl-p1-2 isolated from Lentinula edodes. This hydrolase specifically removes C-7 xylose from 7-β-xylosyltaxanes to form 7-β-hydroxyltaxanes, which can be used for the semi-synthesis of paclitaxel or its analogues. In our present study, we established a high-cell-density fermentation of the recombinant Pichia pastoris harboring the Lxyl-p1-2 gene. Moreover, we further optimized the fermentation conditions, including the initial cell density and the dissolved oxygen level in the induction phase. Under optimized conditions, the biomass of 312.3 g/l (wet cell weight, WCW) was obtained, and the biomass activity of the recombinant enzyme reached 6.55 × 10(4) U/g (WCW). The freeze-dried cells (32 g/l) were used to convert 7-β-xylosyltaxanes (10 g/l, 7-β-xylosyl-10-deacetyltaxol = 62.12 %) in a 5-l reaction volume, and a bioconversion rate about 80 % was achieved. The product purification was performed by ethyl acetate, silica gel chromatography, and preparative HPLC (prep-HPLC), yielding 15.13 g of 10-deacetyltaxol, 3.07 g of 10-deacetylcephalomanine, and 3.47 g of 10-deacetyltaxol C, respectively. In addition, the average recovery rate was around 70 %. Our work provided a foundation for the industrial utilization of the recombinant enzyme on the semi-synthesis of paclitaxel using 7-β-xylosyltaxanes.

Development of an industrial medium and a novel fed-batch strategy for high-level expression of recombinant β-mananase by Pichia pastoris

An industrial medium, Corn Steep Liquor Powder Dextrose (CSD medium) was developed for constitutive expression of recombinant β-mananase by Pichia pastoris. The β-mananase activity (513 U/mL) with CSD medium was 1.64- and 2.5-fold higher than with YPD and BSM in shaken flasks. The β-mananase productivity with CSD medium was 61.0 U/mL h, which was 1.7- and 2.5-fold higher than with YPD and BSM in a 5-L fermenter based on a novel fed-batch strategy combining the real-time exponential feed mode with the DO-stat feed mode. The β-mananase activity, dry cell weight and the recombinant enzyme reached up to 5132 U/mL, 110.0 g/L and 4.50 g/L after 50 h cultivation in a 50-L fermenter. The high efficient expression of recombinant β-mananase by P. pastoris indicated that CSD medium and the novel fed-batch strategy have great potential for the production of recombinant β-mananase in industrial fermentation.

Incomplete protein disulphide bond conformation and decreased protein expression result from high cell growth during heterologous protein expression in Pichia pastoris

Previous report has shown that the expression of recombinant human consensus interferon-α mutant (cIFN) in Pichia pastoris in bioreactor is limited with respect to the incorrectly folded cIFN with incomplete disulfide bond, which lead to the degradation and aggregation of cIFN. In this study, the origin of incorrectly folded cIFN is firstly studied. Fed-batch fermentation in bioreactor shows that the incorrectly folded cIFN is formed intramolecularly and secreted to the extracellular environment. Further chemostat cultures indicate that the specific growth rate is the critical factor for the production of incorrect cIFN. In addition, cell shows reduced expression level of cIFN at high specific growth rate. We also demonstrate that the incorrectly folded cIFN could form aggregates intracellularly and these aggregates are non-covalent forms. Taken together, these results suggest that the efficient heterologous expression of cIFN is limited by high cell growth that is unique from expression limitations seen for soluble proteins. A balance has to be found between the increase for high efficient expression of heterologous proteins and requirement of the high cell growth during the expression of recombinant proteins in P. pastoris.

Synthesis, characterization and assessment of suitability of trehalose fatty acid esters as alternatives for polysorbates in protein formulation

Nonionic polyethylene glycol-derived surfactants are today's choice as surfactants in protein formulations. Different groups discovered that although surface-induced stresses are reduced by these excipients, the long-term stability of different proteins decreased due to polyethylene glycol-related induction of oxidation processes under static storage conditions. In this paper, the potential of polyoxyethylene-free surfactants for protein formulation was evaluated. Three different sugar-based surfactants, 6-O-monocaprinoyl-α,α-trehalose, 6-O-monolauroyl-α,α-trehalose and 6-O-monopalmitoyl-α,α-trehalose, were synthesized in four reaction steps. These substances lack polyethylene glycol residues and can be produced from renewable resources. The chemical and physical properties of these three surfactants were investigated and compared with polysorbate 20 and 80. 6-O-monopalmitoyl-α,α-trehalose was insoluble in water at room temperature and was hence excluded from some of the further tests. The critical micellar concentration of all surfactants is in a comparable range of approximately 0.001-0.01% (m/V). The sugar-based surfactants showed slightly higher hemolytic activity than the polysorbate references. The surfactants with shorter chain length proved to be comparable to polysorbates in regard to physicochemical properties. Finally for human growth hormone, the protein-stabilizing properties against shaking-induced stress were tested and compared to polysorbate-containing formulations. Whereas in the absence of surfactant, dramatic monomer loss and aggregate formation occurred, it was found that 100% monomer content was maintained when 0.1% (m/V) 6-O-monocaprinoyl-α,α-trehalose or 6-O-monolauroyl-α,α-trehalose was added to the formulation. Polysorbate 80 at a concentration of 0.1% (m/V) also significantly stabilized the protein. Lower amounts of surfactants result in only partial stabilization. Furthermore, adsorption of human growth hormone to the container surface is reduced in the presence of the surfactants. Thus, the new sugar-based surfactants offer a promising alternative and have potential for application in protein formulations.

Strategies to maximize expression of rightly processed human interferon alpha2b in Pichia pastoris

The human interferon alpha 2b (IFN alpha2b) belongs to the interferon family of cytokines that exerts many biological functions like inhibition of virus multiplication, repression of tumour growth and other immunological functions. Herein, a synthetic gene coding for human IFN alpha2b was cloned and integrated into a methylotropic yeast-Pichiapastoris. The recombinant human IFN alpha2b protein (approximately 19kDa) could be successfully expressed in Pichiapastoris to a level of nearly 300mg/L with nearly 93% recovery on purification using a single anion exchange chromatography step. A novel media component dimethyl sulphoxide (DMSO) was found to aid in expression of rightly processed IFN alpha2b form with dramatic reduction in the expression of a 20kDa IFN isoform contaminant frequently observed by other workers. The identity of the 20kDa isoform was confirmed by N terminal sequencing which showed extra eleven amino acids at the N terminal portion of the IFN molecule obtained due to incorrect processing by the host KEX2 protease. The purified IFN alpha2b (19kDa) preparation was confirmed by N terminal sequencing, and characterized by MALDI-TOF and Agilent 2100 Bioanalyzer. The bioassay of the recombinant protein gave a specific activity of >2x10(8)IU/mg.