Protein expression in yeast; comparison of two expression strategies regarding protein maturation

Studies to analyse the relationship between IFNα2b gene dosage and its expression, using a Pichia pastoris-based expression system

Human interferon α2b (hIFNα2b) is the most important member of the interferon family. Escherichia coli, yeasts, mammalian cell cultures and baculovirus-infected insect cells have been used for expressing recombinant human interferon. Recently a Pichia pastoris-based expression system has emerged as an attractive system for producing functional human recombinant IFNα2b. In this regard, gene dosage is considered an important factor in obtaining the optimum expression of recombinant protein, which may vary from one protein to another. In the present study we have shown the effect of IFNα2b gene dosage on extracellular expression of IFNα2b recombinant protein from P. pastoris. Constructs containing from one to five repeats of IFNα2b-expressing cassettes were created via an in vitro multimerization approach. P. pastoris host strain X-33 was transformed using these expression cassettes. Groups of P. pastoris clones transformed with different copies of the IFNα2b expression cassette were screened for intrachromosomal integration. The IFNα2b expression level of stable transformants was checked. The copy number of integrated IFNα2b was determined by performing qPCR of genomic DNA of recombinant P. patoris clones. It was observed that an increase in copy number generally had a positive effect on the expression level of IFNα2b protein. Regarding the performance of multicopy strains, those obtained from transformation of multicopy vectors showed relatively high expression, compared to those generated using transformation vector having only one copy of IFNα2b. It was also observed that an increase in drug resistance of a clone did not guarantee its high expression, as integration of a marker gene did not always correlate with integration of the gene of interest.

Use of the yeast Pichia pastoris as an expression host for secretion of enterocin L50, a leaderless two-peptide (L50A and L50B) bacteriocin from Enterococcus faecium L50

In this work, we report the expression and secretion of the leaderless two-peptide (EntL50A and EntL50B) bacteriocin enterocin L50 from Enterococcus faecium L50 by the methylotrophic yeast Pichia pastoris X-33. The bacteriocin structural genes entL50A and entL50B were fused to the Saccharomyces cerevisiae gene region encoding the mating pheromone alpha-factor 1 secretion signal (MFalpha1(s)) and cloned, separately and together (entL50AB), into the P. pastoris expression and secretion vector pPICZalphaA, which contains the methanol-inducible alcohol oxidase promoter (P(AOX1)) to express the fusion genes. After transfer into the yeast, the recombinant plasmids were integrated into the genome, resulting in three bacteriocinogenic yeast strains able to produce and secrete the individual bacteriocin peptides EntL50A and EntL50B separately and together. The secretion was efficiently directed by MFalpha1(s) through the Sec system, and the precursor peptides were found to be correctly processed to form mature and active bacteriocin peptides. The present work describes for the first time the heterologous expression and secretion of a two-peptide non-pediocin-like bacteriocin by a yeast.

Development of bacteriocinogenic strains of Saccharomyces cerevisiae heterologously expressing and secreting the leaderless enterocin L50 peptides L50A and L50B from Enterococcus faecium L50

A segregationally stable expression and secretion vector for Saccharomyces cerevisiae, named pYABD01, was constructed by cloning the yeast gene region encoding the mating pheromone alpha-factor 1 secretion signal (MFalpha1(s)) into the S. cerevisiae high-copy-number expression vector pYES2. The structural genes of the two leaderless peptides of enterocin L50 (EntL50A and EntL50B) from Enterococcus faecium L50 were cloned, separately (entL50A or entL50B) and together (entL50AB), into pYABD01 under the control of the galactose-inducible promoter P(GAL1). The generation of recombinant S. cerevisiae strains heterologously expressing and secreting biologically active EntL50A and EntL50B demonstrates the suitability of the MFalpha1(s)-containing vector pYABD01 to direct processing and secretion of these antimicrobial peptides through the S. cerevisiae Sec system.

Identification of a ligand for IgG-Fc derived from a soluble peptide library based on fusion proteins secreted byS. cerevisiae

Biological libraries are important tools in the development of new peptide-based compounds. Here, we describe the use of a soluble peptide library system as a complementary tool in the field of ligand development. Random peptides were expressed in S. cerevisiae as carboxy-terminal extensions of the eukaryotic initiation factor 5a (eIF5a) and secreted into the culture supernatant. Expression and screening of this library were performed in a microwell format. As an example of this versatile approach, we describe the identification of a ligand for the human IgG-Fc fragment. Ligands binding IgG-Fc show great potential in a wide variety of applications including development of therapeutics, streamlining the large-scale purification of antibodies, and applications in diagnostic tests. We demonstrated the utility of this system. After screening only 6160 clones, we identified a ligand with the peptide sequence of TRRRTCSPPTWPRARARSTPSGCSSTGPSANRG. An affinity constant of 3.9 x 10(5) M(-1) was determined by a biosensor method. Handling and maintenance of this library is conceptually simple and highly applicable for automated high-throughput systems.

Genetically glycosylated ovomucoid third domain can modulate Immunoglobulin E antibody production and cytokine response in BALB/c mice

BACKGROUND

Food allergies are on the rise and it is estimated that in North America, 8% of the children and 4% of the adults have food allergies. Food allergies tend to occur more often in children than in adults due to their immature digestive and immune systems. Hen's egg is among the most common cause of food-induced allergic reactions in North America.

OBJECTIVE

The present study was undertaken to investigate the role of N-glycans of the third domain of ovomucoid in IgE binding and modulation of allergen-specific immune response in BALB/c mice.

METHODS

The cDNA encoding the third domain of ovomucoid was inserted into the yeast genome and expressed in Pichia pastoris X-33 cells, under the control of the glyceraldehyde-3-phosphate (GAP) dehydrogenase promoter for constitutive expression to obtain a post-translationally modified and functionally active ovomucoid third domain. Upon expression, the protein was secreted into the extracellular medium and was purified by size exclusion chromatography. The recombinant protein was produced at 10 mg/L of the culture supernatant. BALB/c mice were sensitized with the recombinant and native forms of glycosylated ovomucoid third domain antigen. The allergic response of the native and the recombinant glycosylated forms of ovomucoid third domain antigens were compared using antibody and cytokine measurements.

RESULTS

ELISA tests indicated a significant decrease in specific IgE antibodies to the recombinant N-linked glycosylated form (P-Gly), when compared with the native glycosylated form (DIII+) using mice sera. Immunization with P-Gly induced the production of IFN-gamma [T-helper type 1 (Th1) response] and lowered the production of IL-4 (Th2 response), and a skewed balance towards the Th1 cytokine demonstrated that P-Gly has a modulating ability on Th1/Th2 balance to down-regulate Th2 response. Furthermore, N-linked glycan (N28) in the third domain of ovomucoid was shown to be associated with suppression of the allergic response.

CONCLUSION

Therefore, we can conclude that P-Gly facilitates and contributes to the discovery of new molecular target for the development of a safe and specific therapeutic vaccine for the treatment of egg allergy, and oligosaccharides do seem to play a major role in the suppression of IgE-binding activity.

Generic method for quantification of FLAG-tagged fusion proteins by a real time biosensor

Availability of rapid quantitative protein-expression analysis is often the bottleneck in high throughput screening applications. A real time biosensor was employed to establish a quantitative assay for FLAG fusion proteins using FLAG-tagged bacterial alkaline phosphatase as standard. A range of FLAG-tagged bacterial alkaline phosphatase concentrations were injected over the anti-FLAG M2 antibody surface of the biosensor and used as standards to determine the concentration of different FLAG-tagged proteins with a molecular mass of 18.1 kDa respectively 49.3 kDa from yeast culture supernatants. The M2 immobilized chip was found to retain binding capacity following regeneration for at least 120 cycles. This real time biosensor method allows the quantitation of proteins from culture supernatants using a calibration curve obtained with a different protein. Further benefits include the short assay time of approximately 5 min, the small amount of sample required (35 microl per injection) and the ability to monitor the binding event in real time.

Peptides derived from a secretory yeast library restore factor VIII activity in the presence of an inhibitory antibody

The development of autoantibodies against factor VIII represents one of the major complications in the treatment of hemophilia A patients. We have employed a novel library system to obtain peptides that specifically neutralize the interaction between factor VIII and these inhibitors. The random peptides are presented as carboxy-terminal extensions of the eukaryotic initiation factor 5a, an intracellular protein with a molecular mass of 18 kDa. These random peptides formed an unique binding site, as demonstrated by molecular simulations using the computer programs InsightII and GROMACS. The library was screened to identify peptides binding to the murine monoclonal anti-factor VIII antibody ESH8 and to inhibitors derived from patients with factor VIII antibodies. Ten peptides binding to ESH8 were identified. Their specificity was confirmed by displacement assays. Two peptides with the sequences STKTLGRPLHGPAGPVEGGALAGVAEDADLVTAVSGR and YHCKREDLTDRDATCALRQPPQAVRGLGPRVTAVSGR showed the ability to restore the factor VIII activity from 33% up to approximately 90% in functional tests performed in vitro. Three candidates for binding to factor VIII antibodies derived from four different patient's sera were achieved. Three fusion proteins with the peptide sequences PQLGSRRSTTPSLTFQNASWFPAGGPCARSNRG, SGSRQVCKLARSLQPF and WERGRRVGAQVRHARHLVARVLDGAGHQARLTAVNGP bound to inhibitors derived from different patients. Furthermore, two of the obtained fusion proteins with the peptide sequences RHWTALGPAPTHTCADLNYPLLS and WERGRRVGAQVRHARHLVARVLDGAGHQARLTAVNGP did also bind to the monoclonal antibody ESH8. This study demonstrates the potential of this system to identify peptides that inhibit the activity of potent inhibitory antibodies and also shows potential as a method for screening of bioactive peptides.

A platform for high-throughput expression of recombinant human enzymes secreted by insect cells

Functional genomics and proteomics have been fields of intense investigation, since the disclosure of the sequence of the human genome. To contribute to the assignment of a physiological role to the vast number of coding genes with unknown function, we have undertaken a program to clone, express, purify and determine the catalytic activity of those enzymes predicted to enter the secretory pathway, focusing our efforts on human peptidases. Our strategy to promote high-throughput expression and purification of recombinant proteins secreted by insect cells relies on the expression of the target enzymes with their native leader sequences and on the carboxyl-terminal fusion with a poly-histidine tag. Growth of host cells were optimized in 24-well format to achieve highly paralleled culture conditions with production yields comparable to shake flask. The purification was performed by a robotic system in 96-well format using either magnetic beads or minicolumns. In a pilot study using reference peptidases and lipases, the high-throughput approach demonstrated to support the secretion in the insect cell medium of 85% of the sample enzymes. Of them, 66% have been proven to be catalytically active using fluorescent homogeneous assays in 384-well format compatible with the high-throughput screening criteria. The implications of these results are discussed in light of the application of this procedure to genomic-predicted peptidases.

Expression of CB2 cannabinoid receptor in Pichia pastoris

To facilitate purification and structural characterization, the CB2 cannabinoid receptor is expressed in methylotrophic yeast Pichia pastoris. The expression plasmids were constructed in which the CB2 gene is under the control of the highly inducible promoter of P. pastoris alcohol oxidase 1 gene. A c-myc epitope and a hexahistidine tag were introduced at the C-terminal of the CB2 to permit easy detection and purification. In membrane preparations of CB2 gene transformed yeast cells, Western blot analysis detected the expression of CB2 proteins. Radioligand binding assays demonstrated that the CB2 receptors expressed in P. pastoris have a pharmacological profile similar to that of the receptors expressed in mammalian systems. Furthermore, the epitope-tagged receptor was purified by metal chelating chromatography and the purified CB2 preparations were subjected to digestion by trypsin. MALDI/TOF mass spectrometry analysis of the peptides extracted from tryptic digestions detected 14 peptide fragments derived from the CB2 receptor. ESI mass spectrometry was used to sequence one of these peptide fragments, thus, further confirming the identity of the purified receptor. In conclusion, these data demonstrated for the first time that epitope-tagged, functional CB2 cannabinoid receptor can be expressed in P. pastoris for purification.

Expression and purification of homogenous proteins in Saccharomyces cerevisiae based on ubiquitin-FLAG fusion

The construction of an expression vector for increased expression of cytoplasmic proteins in Saccharomyces cerevisiae is described. To enhance the yield of expressed proteins, fusion of ubiquitin to an octapeptide (a FLAG tag) upstream of the respective model genes was applied. During protein maturation ubiquitin is efficiently removed by yeast autologous hydrolases, generating the FLAG octapeptide at the N-terminus. Fusion proteins were recognized by the specific monoclonal antibody M1 directed against the FLAG tag. The FLAG-tagged proteins were purified to homogeneity by immunoaffinity chromatography using an anti-FLAG M1 agarose. Different model proteins, green fluorescent protein, green fluorescent protein-human lysozyme, green fluorescent protein elongation-initiahon factor 5a, green fluorescent protein-rapamycin-selective 25-kDa immunophilin, and green fluorescent protein-heat shock protein 90 beta have been selected to demonstrate the efficiency of the new vector construct.

The FLAG peptide, a versatile fusion tag for the purification of recombinant proteins

A fusion tag, called FLAG and consisting of eight amino acids (AspTyrLysAspAspAspAspLys) including an enterokinase-cleavage site, was specifically designed for immunoaffinity chromatography. It allows elution under non-denaturing conditions [Bio/Technology, 6 (1988) 1204]. Several antibodies against this peptide have been developed. One antibody, denoted as M1, binds the peptide in the presence of bivalent metal cations, preferably Ca(+). Elution is effected by chelating agents. Another strategy is competitive elution with excess of free FLAG peptide. Antibodies M2 and M5 are applied in this procedure. Examples demonstrating the versatility, practicability and limitations of this technology are given.