Heterologous Protein Expression Levels Research Articles

Over-expression of xylanolytic -glucuronidase from Thermotoga maritima in the pHsh system of Escherichia coli for the production of xylobiose from xylan

The GH67∝-glucuronidase encoded by aguA of Thermotoga maritima is one of the most thermostable ∝- glucuronidases described to date and thus has considerable potential in industrial application. The enzyme was higher expressed by using the novel pHsh expression vector than in pET vector in Echerichia coli. The site directed mutations changed codons for the first two arginines, a leucine and a proline in the 5’ flanking region of aguA to CGU, CUG and CCG respectively, resulted in a maximum activity of 7.1 U mg-1 in pHsh system. The results of calculation using MFOLD showed the introduction of replacement of the nucleotides encoding the N-terminal region of the protein by optimizing rare codons based on reducing the mRNA secondary structures in TIR is a useful approach to increase the expression level of heterologous proteins in E. coli cells. The ∝-glucuronidase of T. maritima was clearly able to remove 4-O-methylglucuronic acid groups from polymeric xylan and its fragment oligosaccharides. The enzyme acts synergistically with xylanase and beta-xylosidase in the hydrolysis of birchwood xylan and 4-O-methyl-D-glucuronoxylan. Enzymatic hydrolysis of corncob xylan examined by HPLC showed that more xylobiose was produced by xylanase hydrolysis in the presence of ∝- glucuronidase.

Transfection of insect cell lines using polyethylenimine.

Insect cell lines have been widely used in recombinant baculovirus expression systems and transient gene expression studies. Critical to these applications have been the transfection of foreign DNA. This has been frequently done using labor intensive and cytotoxic liposome-based transfection reagents. In the current study we have optimized a new kind of polyethylenimine-based DNA transfection reagent on the Spodoptera frugiperda Sf9 insect cell line. A plasmid vector that transiently expresses green fluorescent protein (GFP) was effectively delivered into Sf9 cells. A transfection efficiency of 54% and cell viability of 85-90% were obtained for Sf9 cells. The developed transfection protocol has now been successfully used to transfect eight insect cell lines derived from Bombyx mori, Trichoplusia ni, Helicoverpa zea, Heliothis virescens and S. frugiperda with GFP and GUS with transfection efficiencies of at least 45%. This method provides high heterologous protein expression levels, transfection efficacy and cell viability, and could be used for transient gene expression in other lepidopteran cell lines.

Improvement of Human lysozyme Expression in Transgenic Rice Grain by Combining Wheat (Triticum aestivum) puroindoline b and Rice (Oryza sativa) Gt1 Promoters and Signal Peptides

Heterologous protein expression levels in transgenic plants are of critical importance in the production of plant-made pharmaceuticals (PMPs). We studied a puroindoline b promoter and signal peptide (Tapur) driving human lysozyme expression in rice endosperm. The results demonstrated that human lysozyme expressed under the control of the Tapur cassette is seed-specific, readily extractable, active, and properly processed. Immuno-electron microscopy indicated that lysozyme expressed from this cassette is localized in protein bodies I and II in rice endosperm cells, demonstrating that this non-storage promoter and signal peptide can be used for targeting human lysozyme to rice protein bodies. We successfully employed a strategy to improve the expression of human lysozyme in transgenic rice grain by combining the Tapur cassette with our well established Gt1 expression system. The results demonstrated that when the two expression cassettes were combined, the expression level of human lysozyme increased from 5.24 +/- 0.34 mg(-1) g flour for the best single cassette line to 9.24 +/- 0.06 mg(-1) g flour in the best double cassette line, indicating an additive effect on expression of human lysozyme in rice grain.

Construction of a novel kind of expression plasmid by ho-mologous recombination in Saccharomyces cerevisiae

Based on a previously used plasmid pHC11, a new plasmid pHC11R was constructed. Cutting plasmid pHC11R with proper restriction enzymes, the resulting larger DNA fragment pHC11R' was co-transformed with a PCR amplified expression cassette of human IFNalpha2b into yeast. By means of the homologous sequences at both ends of two DNA fragments, a novel expression plasmid pHC11R-IFNalpha2b was formed via homologous recombination in the yeast. Compared with pHC11-IFNalpha2b, the expression plasmid pHC11R-IFNalpha2b was smaller in size and in absence of antibiotic resistant gene. The stability and copy number of pHC11R-IFNalpha2b were greatly increased and the expression level of heterologous protein was improved. As the derivatives of pHC11R, a series of recombination expression vectors pHRs containing different combination of expression elements were developed. This led to a rapid and powerful method for cloning and expressing of different genes in yeast.

Spontaneous excision of BAC vector sequences from bacmid-derived baculovirus expression vectors upon passage in insect cells.

Repeated baculovirus infections in cultured insect cells lead to the generation of defective interfering viruses (DIs), which accumulate at the expense of the intact helper virus and compromise heterologous protein expression. In particular, Autographa californica multicapsid nucleopolyhedovirus (AcMNPV) DIs are enriched in an origin of viral DNA replication (ori) not associated with the homologous regions (hrs). This non-hr ori is located within the coding sequence of the non-essential p94 gene. We investigated the effect of a deletion of the AcMNPV non-hr ori on the heterologous protein expression levels following serial passage in Sf21 insect cells. Using homologous ET recombination in E. coli, deletions within the p94 gene were made in a bacterial artificial chromosome (BAC) containing the entire AcMNPV genome (bacmid). All bacmids were equipped with an expression cassette containing the green fluorescent protein gene and a gene encoding the classical swine fever virus E2 glycoprotein (CSFV-E2). For the parental (intact) bacmid only, a strong accumulation of DIs with reiterated non-hr oris was observed. This was not observed for the mutants, indicating that removal of the non-hr ori enhanced the genetic stability of the viral genome upon passaging. However, for all passaged viruses it was found that the entire BAC vector including the expression cassette was spontaneously deleted from the viral genome, leading to a rapid decrease in GFP and CSFV-E2 production. The rationale for the (intrinsic) genetic instability of the BAC vector in insect cells and the implications with respect to large-scale production of proteins with bacmid-derived baculoviruses are discussed.

High-level expression of porcine liver cytochrome P-450 reductase catalytic domain in Escherichia coli by modulating the predicted local secondary structure of mRNA.

A direct expression system for the solubilized catalytic domains of NADPH-cytochrome P-450 reductase (sCPR) from rat (RsCPR) and porcine (PsCPR) in Escherichia coli cells was constructed using the expression plasmid pCWori(+). PsCPR was minimally expressed, whereas RsCPR was highly expressed. Replacement of the nucleotides encoding Thr(60)Ser(61)Ser(62) in PsCPR with those for Ala(60)Pro(61)Pro(62) in RsCPR markedly increased the expression level of the protein. The local secondary structures of the mRNAs, which were predicted with the prediction program GeneBee (http://www.genebee.msu.su), suggested that the intramolecular double strand between the ribosome binding site (RBS) and the Thr(60)Ser(61)Ser(62) codons in PsCPR, and/or the base-pairing at the initiation codon of the mRNAs significantly affected protein expression. Silent mutations were systematically introduced into the codons for Thr(58) and Thr(60)Ser(61) in PsCPR to modulate the local secondary structure of the mRNA. The expression level of the silently mutated PsCPR suggests that the expression level of PsCPR depends on the stability of the local structure at the RBS in the mRNA. A high-level expression system for wild-type PsCPR was constructed by introducing silent mutations at the codons for Thr(60)Ser(61) in PsCPR. The purified PsCPR showed the characteristic absorption spectral changes of sCPR after reduction with NADPH. The yield of purified PsCPR from 1 liter of culture fluid was 45.8 mg. These results substantiate that the introduction of silent mutations in the section of the gene encoding the N-terminal region of the protein based on the predicted local secondary structure of the mRNA at the RBS is a useful approach to control and increase the expression level of heterologous proteins in E. coli cells.

Expression level of heterologous proteins in Pichia pastoris is influenced by flask design.

The yeast Pichia pastoris is a convenient production system that enables expression of heterologous proteins in high amounts. As a fermentation method, shaking flasks are very popular because of their simplicity of handling and their low cost. We compared the expression level of the enzyme acetylcholinesterase in a transformed strain of P. pastoris grown in different flasks, presenting various designs but all with the same volume. A several-thousand-fold difference appeared in the expression levels; and the results could not be explained by differences between the flasks in the oxygenation of the medium. The data show that flask design is an important factor to consider for optimising fermentation processes.

Yield improvement of heterologous peptides expressed in yps1-disrupted Saccharomyces cerevisiae strains

Heterologous protein expression levels in Saccharomyces cerevisiae fermentations are highly dependent on the susceptibility to endogenous yeast proteases. Small peptides, such as glucagon and glucagon-like-peptides (GLP-1 and GLP-2), featuring an open structure are particularly accessible for proteolytic degradation during fermentation. Therefore, homogeneous products cannot be obtained. The most sensitive residues are found at basic amino acid residues in the peptide sequence. These heterologous peptides are degraded mainly by the YPS1-encoded aspartic protease, yapsin1, when produced in the yeast. In this article, distinct degradation products were analyzed by HPLC and mass spectrometry, and high yield of the heterologous peptide production has been achieved by the disruption of the YPS1 gene (previously called YAP3). By this technique, high yield continuous fermentation of glucagon in S. cerevisiae is now possible.