Large-scale production, purification, and characterisation of recombinant Phaseolus vulgaris phytohemagglutinin E-form expressed in the methylotrophic yeast Pichia pastoris

Antigen specificity affects analysis of natural antibodies

Natural antibodies are used to compare immune systems across taxa, to study wildlife disease ecology, and as selection markers in livestock breeding. These immunoglobulins are present prior to immune stimulation. They are described as having low antigen specificity or polyreactive binding and are measured by binding to self-antigens or novel exogenous proteins. Most studies use only one or two antigens to measure natural antibodies and ignore potential effects of antigen specificity in analyses. It remains unclear how different antigen-specific natural antibodies are related or how diversity among natural antibodies may affect analyses of these immunoglobulins. Using genetically distinct lines of chickens as a model system, we tested the hypotheses that (1) antigen-specific natural antibodies are independent of each other and (2) antigen specificity affects the comparison of natural antibodies among animals. We used blood cell agglutination and enzyme-linked immunosorbent assays to measure levels of natural antibodies binding to four antigens: (i) rabbit erythrocytes, (ii) keyhole limpet hemocyanin, (iii) phytohemagglutinin, or (iv) ovalbumin. We observed that levels of antigen specific natural antibodies were not correlated. There were significant differences in levels of natural antibodies among lines of chickens, indicating genetic variation for natural antibody production. However, line distinctions were not consistent among antigen specific natural antibodies. These data show that natural antibodies are a pool of relatively distinct immunoglobulins, and that antigen specificity may affect interpretation of natural antibody function and comparative immunology.

Recombinant Phaseolus vulgaris phytohemagglutinin L-form expressed in the Bacillus brevis exerts in vitro and in vivo anti-tumor activity through potentiation of apoptosis and immunomodulation

Leukocyte phytohemagglutinin (PHA-L) is a tetrameric isomer of phytohemagglutinin (PHA) purified from the red kidney bean (Phaseolus vulgaris) and is a well-known human lymphocyte mitogen. Due to its antitumor and immunomodulatory effects, PHA-L may serve as a potential antineoplastic agent in future cancer therapeutics. However, various negative consequences of PHA have been reported in the literature as a result of the restricted acquisition methods, including oral toxicity, hemagglutinating activity, and immunogenicity. There is a critical need to explore a new method to obtain PHA-L with high purity, high activity and low toxicity. In this report active recombinant PHA-L protein was successfully prepared by Bacillus brevius expression system, and the antitumor and immunomodulatory activities of recombinant PHA-L were characterized by in vitro and in vivo experiments. The results showed that recombinant PHA-L protein had stronger antitumor effect, and its anti-tumor mechanism was realized through direct cytotoxicity and immune regulation. Importantly, compared with natural PHA-L, the recombinant PHA-L protein showed the lower erythrocyte agglutination toxicity in vitro and immunogenicity in mice. Altogether, our study provides a new strategy and important experimental basis for the development of drugs with dual effects of immune regulation and direct antitumor activity.

Detection of Lectin Protein Allergen of Kidney Beans (Phaseolus vulgaris L.) and Desensitization Food Processing Technology

With the increase of food allergy events related to not properly cooked kidney beans (Phaseolus vulgaris L.), more and more researchers are paying attention to the sensitization potential of lectin, one of the major storage and defensive proteins with the specific carbohydrate-binding activity. The immunoglobulin E (IgE), non-IgE, and mixed allergic reactions induced by the lectins were inducted in the current paper, and the detection methods of kidney bean lectin, including the purification strategies, hemagglutination activity, specific polysaccharide or glycoprotein interactions, antibody combinations, mass spectrometry methods, and allergomics strategies, were summarized, while various food processing aspects, such as the physical thermal processing, physical non-thermal processing, chemical modifications, and biological treatments, were reviewed in the potential of sensitization reduction. It might be the first comprehensive review on lectin allergen detection from kidney bean and the desensitization strategy in food processing and will provide a basis for food safety control.

Cloning, large-scale production and characterization of fusion protein (P-TUFT-ALT-2) of Brugian abundant larval transcript-2 with tuftsin in Pichia pastoris

Lymphatic filariasis is a "disease of poor people" due to a large section of affected people with economic backwardness. Therefore, successful elimination of this disease requires a cost-effective prophylactic agent such as vaccine along with conventional drugs. The Abundant Larval Transcript-2 (BmALT-2) protein of Brugia malayi has been recognized as the most potential vaccine candidate. Tuftsin, a tetra-peptide immunopotentiator has already shown the enhanced immunogenicity of various vaccine antigens in earlier studies. This study deals with the development of tuft-alt-2 fusion construct and a suitable culture condition for its large-scale production in Pichia pastoris. The recombinant P. pastoris/tuft-alt-2 with 9-11 copies of the gene construct exhibited the highest expression level. The molecular weight of P-TUFT-ALT-2 was determined as 28 kDa in SDS-PAGE including 3 kDa due to glycosylation. The dry cell biomass was 57.4 gL^-1 in the bioreactor. The P-TUFT-ALT-2 expression was measured as about 35 mg L^-1, which was 102% higher than flask culture. The P-TUFT-ALT-2 produced the highest 65,000 IgG peak titer in Balb/c mice. Moreover, P-TUFT-ALT-2 exhibited about 9.46% higher splenocyte proliferation than E. coli expressed E-ALT-2 alone. The enhanced secreted production of P-TUFT-ALT-2 in bioreactor would step up its commercialization as an inexpensive commercial vaccine for human lymphatic filariasis.

Expression of Lectins in Heterologous Systems

Lectins are proteins that have the ability to recognize and bind in a reversible and specific way to free carbohydrates or glycoconjugates of cell membranes. For these reasons, they have been extensively used in a wide range of industrial and pharmacological applications. Currently, there is great interest in their production on a large scale. Unfortunately, conventional techniques do not provide the appropriate platform for this purpose and therefore, the heterologous production of lectins in different organisms has become the preferred method in many cases. Such systems have the advantage of providing better yields as well as more homogeneous and better-defined properties for the resultant products. However, an inappropriate choice of the expression system can cause important structural alterations that have repercussions on their biological activity since the specificity may lay in their post-translational processing, which depends largely on the producing organism. The present review aims to examine the most representative studies in the area, exposing the four most frequently used systems (bacteria, yeasts, plants and animal cells), with the intention of providing the necessary information to determine the strategy to follow in each case as well as their respective advantages and disadvantages.

Demonstration-Scale High-Cell-Density Fermentation of Pichia pastoris

Pichia pastoris has been one of the most successful heterologous overexpression systems in generating proteins for large-scale production through high-cell-density fermentation. However, optimizing conditions of the large-scale high-cell-density fermentation for biochemistry and industrialization is usually a laborious and time-consuming process. Furthermore, it is often difficult to produce authentic proteins in large quantities, which is a major obstacle for functional and structural features analysis and industrial application. For these reasons, we have developed a protocol for efficient demonstration-scale high-cell-density fermentation of P. pastoris, which employs a new methanol-feeding strategy-biomass-stat strategy and a strategy of increased air pressure instead of pure oxygen supplement. The protocol included three typical stages of glycerol batch fermentation (initial culture phase), glycerol fed-batch fermentation (biomass accumulation phase), and methanol fed-batch fermentation (induction phase), which allows direct online-monitoring of fermentation conditions, including broth pH, temperature, DO, anti-foam generation, and feeding of glycerol and methanol. Using this protocol, production of the recombinant β-xylosidase of Lentinula edodes origin in 1000-L scale fermentation can be up to ~900 mg/L or 9.4 mg/g cells (dry cell weight, intracellular expression), with the specific production rate and average specific production of 0.1 mg/g/h and 0.081 mg/g/h, respectively. The methodology described in this protocol can be easily transferred to other systems, and eligible to scale up for a large number of proteins used in either the scientific studies or commercial purposes.

Phaseolus vulgaris lectins: A systematic review of characteristics and health implications

Legume lectins are carbohydrate-binding proteins of non-immune origin. Significant amounts of lectins have been found in Phaseolus vulgaris beans as far back as in the last century; however, many questions about their potential biological roles still remain obscure. Studies have shown that lectins are anti-nutritional factors that can cause intestinal disorders. Owing to their ability to act as toxic allergens and hemagglutinins, the Phaseolus vulgaris lectins are of grave concern for human health and safety. Nonetheless, their potential beneficial health effects, such as anti-cancer, anti-human immunodeficiency virus (anti-HIV), anti-microbial infection, preventing mucosal atrophy, reducing type 2 diabetes and obesity, promoting nutrients absorption and targeting drugs, are of immense interest. The significance of Phaseolus vulgaris lectins in biological researches and the potential biomedical applications have placed tremendous emphasis on the development of purification strategies to obtain the protein in pure and stable forms. These purification strategies entail considerations such as effects of proteolysis, heating, gamma radiation, and high-hydrostatic-pressure that can have crucial outcomes in either eliminating or improving bioactivities of the lectins. Thus, up-to-date research findings of Phaseolus vulgaris lectins on different aspects such as anti-nutritional and health impacts, purification strategies and novel processing trends, are systematically reviewed.

Engineering of recombinant Wisteria floribunda agglutinin specifically binding to GalNAcβ1,4GlcNAc (LacdiNAc)

Wisteria floribunda agglutinin (WFA) is a useful probe for distinguishing glycan structural alterations in diseases such as intrahepatic bile duct carcinoma and hepatic fibrosis; however, the gene encoding WFA has not been identified. Here, we identified the gene encoding WFA, and recombinant WFA (rWFA) was expressed in Escherichia coli and purified. The natural complementary DNA sequence obtained from wisteria seeds contained an open reading frame of 861 nucleotides encoding a WFA precursor, which included a hydrophobic signal peptide at the N-terminus, a propeptide at the C-terminus and a single cysteine (Cys) residue for dimer formation. We characterized the natural and rWFA by the glycoconjugate microarray and frontal affinity chromatography. rWFA exhibited glycan binding specificity similar to that of natural WFA: both bound to Gal- and N-acetylgalactosamine (GalNAc)-terminated glycans. Moreover, the engineered WFA with an amino acid substitution in Cys-272 yielded a recombinant monomeric lectin with limited binding specificity but wild-type affinity for GalNAc-terminated glycans, specifically GalNAcβ1,4GlcNAc. Thus, this engineered lectin may be applied to highly sensitive biomarker detection.

Scaling-up Fermentation of Pichia pastoris to demonstration-scale using new methanol-feeding strategy and increased air pressure instead of pure oxygen supplement

Scaling-up of high-cell-density fermentation (HCDF) of Pichia pastoris from the lab or pilot scale to the demonstration scale possesses great significance because the latter is the final technological hurdle in the decision to go commercial. However, related investigations have rarely been reported. In this paper, we study the scaling-up processes of a recombinant P. pastoris from the pilot (10 to 100-L) to the demonstration (1,000-L) scales, which can be used to convert 7-β-xylosyl-10-deacetyltaxol into 10-deacetyltaxol by the β-xylosidase for semi-synthesis of Taxol. We demonstrated that a pure oxygen supplement can be omitted from the HCDF if the super atmospheric pressure was increased from 0.05 to 0.10 ± 0.05 MPa, and we developed a new methanol feeding biomass-stat strategy (0.035 mL/g/h) with 1% dissolved oxygen and 100 g/L initial induction biomass (dry cell weight). The scaling-up was reproducible, and the best results were obtained from the 1,000-L scale, featuring a shorter induction time and the highest enzyme activities and productions, respectively. The specific growth and specific production rates were also determined. This study lays a solid foundation for the commercial preparation of 10-deacetyltaxol through the recombinant yeast. It also provides a successful paradigm for scaling-up HCDF of P. pastoris to the demonstration scale.

Bioprocess and downstream optimization of recombinant bovine chymosin B in Pichia (Komagataella) pastoris under methanol-inducible AOXI promoter

A clone of the methylotrophic yeast Pichia pastoris strain GS115 transformed with the bovine prochymosin B gene was used to optimize the production and downstream of recombinant bovine chymosin expressed under the methanol-inducible AOXI promoter. Cell growth and recombinant chymosin production were analyzed in flask cultures containing basal salts medium with biodiesel-byproduct glycerol as the carbon source, obtaining values of biomass level and milk-clotting activity similar to those achieved with analytical glycerol. The effect of biomass level at the beginning of methanol-induction phase on cell growth and chymosin expression was evaluated, determining that a high concentration of cells at the start of such period generated an increase in the production of chymosin. The impact of the specific growth rate on chymosin expression was studied throughout the induction stage by methanol exponential feeding fermentations in a lab-scale stirred bioreactor, achieving the highest production of heterologous chymosin with a constant specific growth rate of 0.01h(-1). By gel filtration chromatography performed at a semi-preparative scale, recombinant chymosin was purified from exponential fed-batch fermentation cultures, obtaining a specific milk-clotting activity of 6400IMCU/mg of chymosin and a purity level of 95%. The effect of temperature and pH on milk-clotting activity was analyzed, establishing that the optimal temperature and pH values for the purified recombinant chymosin are 37°C and 5.5, respectively. This study reported the features of a sustainable bioprocess for the production of recombinant bovine chymosin in P. pastoris by fermentation in stirred-tank bioreactors using biodiesel-derived glycerol as a low-cost carbon source.

Cloning, expression and optimized production in a bioreactor of bovine chymosin B in Pichia (Komagataella) pastoris under AOX1 promoter

The codon sequence optimized bovine prochymosin B gene was cloned under the control of the alcohol oxidase 1 promoter (AOX1) in the vector pPIC9K and integrated into the genome of the methylotrophic yeast Pichia (Komagataella) pastoris (P. pastoris) strain GS115. A transformant clone that showed resistance to over 4 mg G418/ml and displayed the highest milk-clotting activity was selected. Cell growth and recombinant bovine chymosin production were optimized in flask cultures during methanol induction phase achieving the highest coagulant activity with low pH values, a temperature of 25°C and with the addition of sorbitol and ascorbic acid at the beginning of this period. The scaling up of the fermentation process to lab-scale stirred bioreactor using optimized conditions, allowed to reach 240 g DCW/L of biomass level and 96 IMCU/ml of milk-clotting activity. The enzyme activity corresponded to 53 mg/L of recombinant bovine chymosin production after 120 h of methanol induction. Western blot analysis of the culture supernatant showed that recombinant chymosin did not suffer degradation during the protein production phase. By a procedure that included high performance gel filtration chromatography and 3 kDa fast ultrafiltration, the recombinant bovine chymosin was purified and concentrated from fermentation cultures, generating a specific activity of 800 IMCU/Total Abs(280 nm) and a total activity recovery of 56%. This study indicated that P. pastoris is a suitable expression system for bioreactor based fed-batch fermentation process for the efficient production of recombinant bovine chymosin under methanol-inducible AOX1 promoter.

High-yield production of a chitinase from Aeromonas veronii B565 as a potential feed supplement for warm-water aquaculture

Chitin, present in crustacean shells, insects, and fungi, is the second most plentiful natural organic fiber after wood. To effectively use chitin in a cost-saving and environmentally friendly way in aquaculture, crustacean shells (e.g., shrimp-shell meal) are supplemented into aquafeed after degradation by chemical methods. Herein, we describe a chitinase from Aeromonas veronii B565, designated ChiB565, which potently degrades shrimp-shell chitin and resists proteolysis. We isolated recombinant ChiB565 of the expected molecular mass in large yield from Pichia pastoris. ChiB565 is optimally active at pH 5.0 and 50 °C and stable between pH 4.5 and 9.0 at 50 °C and below. Compared with the commercial chitinase C-6137, which cannot degrade shrimp-shell chitin, ChiB565 hydrolyzes shrimp-shell chitin in addition to colloidal chitin, powdered chitin, and β-1,3-1,4-glucan. The optimal enzyme concentration and reaction time for in vitro degradation of 0.1 g of powdered shrimp shell are 30 U of ChiB565 and 3 h, respectively. A synergistic protein-release effect occurred when ChiB565 and trypsin were incubated in vitro with shrimp shells. Tilapia were fed an experimental diet containing 5% (w/w) shrimp bran and 16.2 U/kg ChiB565, which significantly improved growth and feed conversion compared with a control diet lacking ChiB565. Dietary ChiB565 enhanced nitrogen digestibility and downregulated intestinal IL-1β expression. The immunologically relevant protective effects of dietary ChiB565 were also observed for 2 to 3 days following exposure to pathogenic Aeromonas hydrophila.

Expression analysis of the nucleocytoplasmic lectin 'Orysata' from rice in Pichia pastoris

The Oryza sativa lectin, abbreviated Orysata, is a mannose-specific, jacalin-related lectin expressed in rice plants after exposure to certain stress conditions. Expression of a fusion construct containing the rice lectin sequence linked to enhanced green fluorescent protein in Bright Yellow 2 tobacco cells revealed that Orysata is located in the nucleus and the cytoplasm of the plant cell, indicating that it belongs to the class of nucleocytoplasmic jacalin-related lectins. Since the expression level of Orysata in rice tissues is very low the lectin was expressed in the methylotrophic yeast Pichia pastoris with the Saccharomyces α-factor sequence to direct the recombinant protein into the secretory pathway and express the protein into the medium. Approximately 12 mg of recombinant lectin was purified per liter medium. SDS/PAGE and western blot analysis showed that the recombinant lectin exists in two molecular forms. Far western blot analysis revealed that the 23 kDa lectin polypeptide contains an N-glycan which is absent in the 18.5 kDa polypeptide. Characterization of the glycans present in the recombinant Orysata revealed high-mannose structures, Man9-11 glycans being the most abundant. Glycan array analysis showed that Orysata interacts with high-mannose as well as with more complex N-glycan structures. Orysata has potent anti-human immunodeficiency virus and anti-respiratory syncytial virus activity in cell culture compared with other jacalin-related lectins.

Isolation and characterization of a French bean hemagglutinin with antitumor, antifungal, and anti-HIV-1 reverse transcriptase activities and an exceptionally high yield

A dimeric 64-kDa hemagglutinin was isolated with a high yield from dried Phaseolus vulgaris cultivar "French bean number 35" seeds using a chromatographic protocol that involved Blue-Sepharose, Q-Sepharose, and Superdex 75. The yield was exceptionally high (1.1g hemagglutinin per 100g seed), which is around 10-85 times higher than other Phaseolus cultivars. Its N-terminal sequence resembled those of other Phaseolus hemagglutinins. The hemagglutinating activity of the hemagglutinin was stable in the pH range 6-8, and in the temperature range 0 degrees C-50 degrees C. It inhibited HIV-1 reverse transcriptase with an IC50 of 2microM. It suppressed mycelial growth in Valsa mali with an IC50 of 10microM. It inhibited proliferation of hepatoma HepG2 cells and breast cancer MCF-7 cells with an IC50 of 100 and 2microM, respectively. It had no antiproliferative effect on normal embryonic liver WRL68 cells.

The insecticidal activity of recombinant garlic lectins towards aphids

The heterodimeric and homodimeric garlic lectins ASAI and ASAII were produced as recombinant proteins in the yeast Pichia pastoris. The proteins were purified as functional dimeric lectins, but underwent post-translational proteolysis. Recombinant ASAII was a single homogenous polypeptide which had undergone C-terminal processing similar to that occurring in planta. The recombinant ASAI was glycosylated and subject to variable and heterogenous proteolysis. Both lectins showed insecticidal effects when fed to pea aphids (Acyrthosiphon pisum) in artificial diet, ASAII being more toxic than ASAI at the same concentration. Acute toxicity (mortality at < or =48 h exposure; similar timescale to starvation) was only apparent at the highest lectin concentrations tested (2.0 mg ml(-)1), but dose-dependent chronic toxicity (mortality at >3d exposure) was observed over the concentration range 0.125-2.0 mg ml(-1). The recombinant lectins caused mortality in both symbiotic and antibiotic-treated aphids, showing that toxicity is not dependent on the presence of the bacterial symbiont (Buchnera aphidicola), or on interaction with symbiont proteins, such as the previously identified lectin "receptor" symbionin. A pull-down assay coupled with peptide mass fingerprinting identified two abundant membrane-associated aphid gut proteins, alanyl aminopeptidase N and sucrase, as "receptors" for lectin binding.

Expression of frutalin, an alpha-D-galactose-binding jacalin-related lectin, in the yeast Pichia pastoris

Frutalin is an alpha-D-galactose-binding lectin expressed in breadfruit seeds. Its isolation from plant is time-consuming and results in a heterogeneous mixture of different lectin isoforms. In order to improve and facilitate the availability of the breadfruit lectin, we cloned an optimised codifying frutalin mature sequence into the pPICZalphaA expression vector. This expression vector, designed for protein expression in the methylotrophic yeast Pichia pastoris, contains the Saccharomyces alpha-factor preprosequence to direct recombinant proteins into the secretory pathway. Soluble recombinant frutalin was detected in the culture supernatants and recognised by native frutalin antibody. Approximately 18-20 mg of recombinant lectin per litre medium was obtained from a typical small scale methanol-induced culture purified by size-exclusion chromatography. SDS-PAGE and Edman degradation analysis revealed that frutalin was expressed as a single chain protein since the four amino-acid linker peptide "T-S-S-N", which connects alpha and beta chains, was not cleaved. In addition, incomplete processing of the signal sequence resulted in recombinant frutalin with one Glu-Ala N-terminal repeat derived from the alpha-factor prosequence. Endoglycosidase treatment and SDS-PAGE analysis revealed that the recombinant frutalin was partly N-glycosylated. Further characterisation of the recombinant lectin revealed that it specifically binds to the monosaccharide Me-alpha-galactose presenting, nevertheless, lesser affinity than the native frutalin. Recombinant frutalin eluted from a size-exclusion chromatography column with a molecular mass of about 62-64 kDa, suggesting a tetrameric structure, however it did not agglutinate rabbit erythrocytes as native frutalin does. This work shows that the galactose-binding jacalin-related lectins four amino-acid linker peptide "T-S-S-N" does not undergo any proteolytic cleavage in the yeast P. pastoris and also that linker cleavage might not be essential for lectin sugar specificity.

Eukaryotic expression and antimicrobial spectrum determination of the peptide tachyplesin II

Ta0-a, the gene encoding the mature antimicrobial peptide tachyplesin II, was engineered to optimize the coding sequence according to codon usage bias in yeast. Ta0-a was efficiently expressed in the methylotrophic yeast Pichia pastoris strain SMD1168. The recombinant peptide Ta0 reached 150mg/L after methanol induction for 6 d. Ta0 was rapidly purified to homogeneity by a single step of size-exclusion chromatography. The minimal lethal concentrations of Ta0 to the Escherichia coli strain K12 was 30 microg/mL. Ta0 exhibited a wide range of antimicrobial activity: the growth of 26 bacterial and fungal strains, including some typical food/feed spoilage microorganisms, was all substantially inhibited. This result indicates the potential practical application of the recombinant peptide in various industrial products.

Immunotoxicological studies of genetically modified rice expressing PHA-E lectin or Bt toxin in Wistar rats

As part of the SAFOTEST project the immunmodulating effect of Cry1Ab protein from Bacillus thuringiensis (Bt) and PHA-E lectin from kidney bean (Phaseolus vulgaris erythroagglutinin) was examined in 28- and 90-day feeding studies in Wistar rats. PHA-E lectin was chosen as positive control. Rats were fed control rice, transgenic rice expressing Cry1Ab protein or PHA-E lectin, or transgenic rice spiked with the purified recombinant protein. Total immunoglobulin levels, mitogen-induced cell proliferation, T-dependent antibody response to sheep red blood cells and the antigen-specific antibody response in serum were examined at the end of the studies. A dose-dependent increase in mesenteric lymph node weight and total immunoglobulin A was seen when feeding PHA-E transgenic rice alone or spiked with 0.1% purified PHA-E lectin for 90 days indicating a local effect of PHA-E in the intestine. No adverse effects of Cry1Ab protein were found. An anti-PHA-E and anti-Cry1Ab antibody response was induced both after inhalation (control groups) and after inhalation/ingestion (groups fed recombinant protein alone or together with transgenic rice). In conclusion, only PHA-E lectin was found to have an immunomodulating effect when feeding rats for 90 days with approximately 70 mg PHA-E/kg bodyweight per day. As both PHA-E lectin and Cry1Ab protein were capable of inducing an antigen-specific antibody response it is important to make careful considerations when designing future animal studies to avoid intake of proteins from the other groups by inhalation as well as to examine the sensitization and elicitation potential of 'foreign' proteins before introduction to the world market.

Expression of the nucleocytoplasmic tobacco lectin in the yeast Pichia pastoris

The Nicotiana tabacum lectin, also called Nictaba, is a nucleocytoplasmic plant lectin expressed in tobacco leaves after exposure to jasmonates. Purification of the lectin from raw material is a time-consuming process, demanding large amounts of induced plant material. In addition, the lectin yield is low and purified lectin fractions are always contaminated with low molecular weight compounds such as phenols. In a way to improve and facilitate the purification of the tobacco lectin, we cloned the Nictaba gene in a vector optimized for protein expression in the methylotrophic yeast Pichia pastoris. In this report, we present data of the expression profile of recombinant Nictaba in the P. pastoris culture medium and in P. pastoris cells together with the purification strategy using ion exchange chromatography and affinity chromatography on a column with immobilized ovomucoid. Pichia transformants were estimated to express approximately 6mg of recombinant lectin per liter medium after a 72h culture. SDS-PAGE and Western blot analysis revealed that the recombinant lectin expressed in Pichia exists in two molecular forms. Edman degradation and mass spectrometry analysis confirmed the presence of at least two forms of recombinant lectin with molecular weights of 19,060 and 20,100Da, corresponding to lectin polypeptides similar to the fully processed Nictaba which is N-terminally blocked, and Nictaba extended at the N-terminus with the amino acids residues EAEAYVEFT due to incomplete processing of the alpha-factor mating sequence. Further characterisation of the recombinant lectin revealed agglutination and carbohydrate-binding properties similar to the native tobacco lectin.

Safety testing of GM-rice expressing PHA-E lectin using a new animal test design

The 90-day animal study is the core study for the safety assessment of genetically modified foods in the SAFOTEST project. The model compound tested in the 90-day study was a rice variety expressing the kidney bean Phaseolus vulgaris lectin agglutinin E-form (PHA-E lectin). Female Wistar rats were given a nutritionally balanced purified diet with 60% parental rice, 60% PHA-E rice or 60% PHA-E rice spiked with 0.1% recombinant PHA-E lectin for 90 days. This corresponded to a mean daily PHA-E lectin intake of approximately 0, 30 and 100mg/kg body weight for each group, respectively. The spiking was used to increase the specificity and to demonstrate the sensitivity of the study. A range of biological, biochemical, microbiological and pathological parameters were examined and significant differences in weight of small intestine, stomach and pancreas and plasma biochemistry were seen between groups. Included in this paper are also data from the molecular characterisation and chemical analysis of the PHA-E rice, from the construction and production of the PHA-E lectin, and from the preceding 28-day in vivo study where the toxicity of the pure PHA-E lectin was determined. In conclusion, the combined use of information from the compositional analysis, the 28-day study and the characterisation of the PHA-E rice and the PHA-E lectin has improved the design of the 90-day study. The spiking procedure has facilitated the interpretation of the results of the study and transferred it into a valuable tool for the future safety testing of genetically modified foods.

Functional expression, purification, and characterization of human Flt3 ligand in the Pichia pastoris system

Flt3 ligand (FL) is a potent hematopoietic cytokine that affects the growth and differentiation of hematopoietic progenitor and stem cells both in vivo and in vitro. Pichia pastoris transformants secreting high-level rhFL were obtained using 'yeastern blotting' method and the expression level in liquid was about 30 mg/L. rhFL was purified to about 95% purity with overnight dialysis, filtration and an anion-exchange step. Further purification steps employing Sephacryl S-200 and reverse-phase HPLC raised the purity to over 99%. The purified rhFL possessed correct N-terminal amino acid sequence and positive Western blotting bands. SDS-PAGE and mass spectrometry analysis showed molecular weight of rhFL was about 21 and 34 kDa, suggesting that rhFL was glycosylated. The result of capillary electrophoresis showed that its pI is 3.12-4.72. Endo H deglycosylation analysis indicated that there was O-glycosylation besides N-glycosylation in rhFL secreted from P. pastoris. Bioactivity assay showed that the purified rhFL had dose-dependent expansion activity on bone marrow nucleated cells.

Expression of organophosphorus hydrolase OPHC2 in Pichia pastoris: Purification and characterization

Organophosphorus hydrolase is able to hydrolyze phosphoester bonds and reduce the toxicity of organophosphorus compounds. In this work, recombinant organophosphorus hydrolase OPHC2 was successfully produced by Pichia pastoris at a high expression level (approximately 5.5 g/L) using 3 L high-cell-density fermentation. The expression level is higher than those produced in other expression systems. The results of the SDS-PAGE and the Western blot analyses showed a major 36 kDa polypeptide band, which was the same size as that from the original bacteria, Pseudomonas pseudoalcaligenes C2-1. The expressed enzyme was recovered from the culture supernatant and purified by a single-step purification procedure with a recovery rate of 72.78%. The main physiochemical features of the recombinant OPHC2, including its optimum temperature and pH for the reaction, its temperature and pH stability, and its sensitivity to some metal ions and chemical reagents, were also characterized. With methyl parathion as a substrate, the optimum temperature and pH for enzyme activity are 65 degrees C and pH 9.0, respectively. It also shows good thermal and pH stability.

Recombinant expression of pleurocidin cDNA using the Pichia pastoris expression system

This research utilized the Pichia pastoris expression system for recombinant expression of cDNA of pleurocidin, a small (2.7 kd) antimicrobial peptide isolated from winter flounder (Pleuronectes americanus). The Pichia vector contains the alcohol oxidase gene promoter (AOX 1), which under the induction of methanol allows for expression of heterologous protein gene inserted downstream in the vector. Two strains of P pastoris were used as host cells, the wild type (P pastoris X-33((mut(+)))) and the mutant (P pasatoris KM71H((mut(s))) ). Polymerase chain reaction (PCR) and DNA sequencing showed that pleurocidin cDNA was successfully integrated into the P pastoris genome. Reverse transcription (RT)-PCR showed that pleurocidin was transcribed by both Pichia host strains. Affinity chromatography, SDS-PAGE, and immunological techniques were used for purification and detection of recombinant peptide. Although there was strong evidence of transcription of pleurocidin cDNA, the Pichia system requires further optimization to obtain detectable levels of this small peptide.

Expression and purification of a recombinant avidin with a lowered isoelectric point in Pichia pastoris

A recombinant glycosylated avidin (recGAvi) with an acidic isoelectric point was expressed and secreted by the methylotrophic yeast Pichia pastoris. The coding sequence for recGAvi was de novo synthesized based on the codon usage of P. pastoris. RecGAvi is secreted at approximately 330mg/L of culture supernatant. RecGAvi monomer displays a molecular weight of 16.5kDa, as assessed by ESI mass spectrometry. N-terminal amino acid sequencing indicates the presence of three additional amino acids (E-A-E), which contribute to further lowering the isoelectric point to 5.4. The data presented here demonstrate that the P. pastoris system is suitable for the production of recGAvi and that the recombinant avidin displays biotin-binding properties similar to those of the hen-egg white protein.