Evaluation of inducible promoters on the secretion of a ZZ-proinsulin fusion protein in Escherichia coli

Heterologous Expression of Biopreservative Bacteriocins With a View to Low Cost Production

Bacteriocins, a heterogenous group of antibacterial ribosomally synthesized peptides, have potential as bio-preservatives in in a wide range of foods and as future therapeutics for the inhibition of antibiotic-resistant bacteria. While many bacteriocins have been characterized, several factors limit their production in large quantities, a requirement to make them commercially viable for food or pharma applications. The identification of new bacteriocins by database mining has been promising, but their potential is difficult to evaluate in the absence of suitable expression systems. E. coli has been used as a heterologous host to produce recombinant proteins for decades and has an extensive set of expression vectors and strains available. Here, we review the different expression systems for bacteriocin production using this host and identify the most important features to guarantee successful production of a range of bacteriocins.

Cellular disulfide bond formation in bioactive peptides and proteins

Bioactive peptides play important roles in metabolic regulation and modulation and many are used as therapeutics. These peptides often possess disulfide bonds, which are important for their structure, function and stability. A systematic network of enzymes--a disulfide bond generating enzyme, a disulfide bond donor enzyme and a redox cofactor--that function inside the cell dictates the formation and maintenance of disulfide bonds. The main pathways that catalyze disulfide bond formation in peptides and proteins in prokaryotes and eukaryotes are remarkably similar and share several mechanistic features. This review summarizes the formation of disulfide bonds in peptides and proteins by cellular and recombinant machinery.

Cloning of Soluble Human Stem Cell Factor in pET-26b(+) Vector

PURPOSE

Stem cell factor (SCF) plays an important role in the survival, proliferation and differentiation of hematopoietic stem cells and progenitor cells. Potential therapeutic applications of SCF include hematopoietic stem cell mobilization, exvivo stem/progenitor cell expansion, gene therapy, and immunotherapy. Considering the cost and problem in accessibility of this product in Iran, clears the importance of indigenizing production of rhSCF. In the present work, we describe the construction of the soluble rhSCF expression vector in pET-26b (+) with periplasmic localization potential.

METHODS

Following PCR amplification of human SCF ORF, it is cloned in pET-26b (+) vector in NcoI and XhoI sites. The recombinant construct was transformed into BL21 (DE3) Ecoli strains.

RESULTS

The construction of recombinant vector was verified by colony PCR and sequence analysis of pET26b-hSCF vector. Sequence analyses proved that human SCF ORF has been inserted into NcoI and XhoI site with correct orientation downstream of strong T7 promotor and showed no nucleotide errors.

CONCLUSION

The SCF ORF was successfully cloned in pET-26b (+) expression vector and is ready for future production of SCF protein.

Strategies for successful recombinant expression of disulfide bond-dependent proteins in Escherichia coli

Bacteria are simple and cost effective hosts for producing recombinant proteins. However, their physiological features may limit their use for obtaining in native form proteins of some specific structural classes, such as for instance polypeptides that undergo extensive post-translational modifications. To some extent, also the production of proteins that depending on disulfide bridges for their stability has been considered difficult in E. coli.

Both eukaryotic and prokaryotic organisms keep their cytoplasm reduced and, consequently, disulfide bond formation is impaired in this subcellular compartment. Disulfide bridges can stabilize protein structure and are often present in high abundance in secreted proteins. In eukaryotic cells such bonds are formed in the oxidizing environment of endoplasmic reticulum during the export process. Bacteria do not possess a similar specialized subcellular compartment, but they have both export systems and enzymatic activities aimed at the formation and at the quality control of disulfide bonds in the oxidizing periplasm.

This article reviews the available strategies for exploiting the physiological mechanisms of bactera to produce properly folded disulfide-bonded proteins.

A novel Ecotin-Ubiquitin-Tag (ECUT) for efficient, soluble peptide production in the periplasm of Escherichia coli

Background

Many protocols for recombinant production of peptides and proteins include secretion into the periplasmic space of Escherichia coli, as they may not properly fold in the cytoplasm. If a signal peptide is not sufficient for translocation, a larger secretion moiety can instead be fused to the gene of interest. However, due to the covalent linkage of the proteins, a protease recognition site needs to be introduced in between, altering the N-terminus of the product. In the current study, we combined the ubiquitin fusion technology, which allows production of authentic peptides and proteins, with secretion by the perpiplasmic protease inhibitor ecotin.

Results

Different fusion constructs, composed of ecotin, mouse ubiquitin b and a model peptide, were expressed in E. coli BL21(DE3). The fusion proteins were translocated into the periplasmic space and the ecotin signal peptide was cleaved off. Under the control of the lacUV5 promoter at 24°C we obtained 18 mg periplasmic recombinant protein per gram dry cell weight. However, vigorous expression with the T7 promoter caused outer membrane permeabilization and leakage of the fusion protein into the culture medium. Target peptides were released from hybrid proteins by the deubiquitinating enzyme ubiquitin c-terminal hydrolase-L3 in vitro. MALDI TOF-TOF mass spectroscopy confirmed accurate cleavage.

Conclusion

This newly described method represents a useful technique for the production of authentic soluble peptides in the periplasm of E. coli. In addition, larger proteins might also be produced with the current system by the use of ubiquitin specific proteases, which can cleave off larger C-terminal extensions.

Time-course determination of plasmid content in eukaryotic and prokaryotic cells using real-time PCR

A Real-Time PCR method was developed to monitor the plasmid copy number (PCN) in Escherichia coli and Chinese hamster ovary (CHO) cells. E. coli was transformed with plasmids containing a ColE1 or p15A origin of replication and CHO cells were transfected with a ColE1 derived plasmid used in DNA vaccination and carrying the green fluorescent protein (GFP) reporter gene. The procedure requires neither specific cell lysis nor DNA purification and can be performed in <30 min with dynamic ranges covering 0.9 pg-55 ng, and 5.0 pg-2.5 ng of plasmid DNA (pDNA) for E. coli and CHO cells, respectively. Analysis of PCN in E. coli batch cultures revealed that the maximum copy number per cell is attained in mid-exponential phase and that this number decreases on average 80% towards the end of cultivation for both types of plasmids. The plasmid content of CHO cells determined 24 h post-transfection was around 3 x 104 copies per cell although only 37% of the cells expressed GFP one day after transfection. The half-life of pDNA was 20 h and around 100 copies/cell were still detected 6 days after transfection.

Periplasmic targeting of recombinant proteins in Escherichia coli

Targeting recombinant protein production to the periplasmic space of Escherichia coli presents several advantages over cytoplasmic production in inclusion bodies and at the same time overcomes the low productivity problem often associated with culture medium secretion. This chapter presents a strategy for periplasmic production of recombinant proteins fused to synthetic Z domains derived from staphylococcal protein A. Expression, purification, and monitoring strategies are discussed using green fluorescent protein and human proinsulin as model proteins.

Recombinant protein secretion in Escherichia coli

The secretory production of recombinant proteins by the Gram-negative bacterium Escherichia coli has several advantages over intracellular production as inclusion bodies. In most cases, targeting protein to the periplasmic space or to the culture medium facilitates downstream processing, folding, and in vivo stability, enabling the production of soluble and biologically active proteins at a reduced process cost. This review presents several strategies that can be used for recombinant protein secretion in E. coli and discusses their advantages and limitations depending on the characteristics of the target protein to be produced.

Evaluation of bottlenecks in proinsulin secretion by Escherichia coli

This work evaluates three potential bottlenecks in recombinant human proinsulin secretion by Escherichia coli: protein stability, secretion capacity and the effect of molecular size on secretion efficiency. A maximum secretion level of 7.2 mg g(-1) dry cell weight was obtained in the periplasm of E. coli JM109(DE3) host cells. This value probably represents an upper limit in the transport capacity of E. coli cells secreting ZZ-proinsulin and similar proteins with the protein A signal peptide. A selective deletion study was performed in the fusion partner and no effect of the molecular size (17-24 kDa) was detected on secretion efficiency. The protective effect against proteolysis provided by the ZZ domain was thoroughly demonstrated in the periplasm of E. coli and it was also shown that a single Z domain is able to provide the same protection level without compromising the downstream processing. The use of this shorter fusion partner enables a 1.6-fold increase in the recovery of the target protein after cleavage of the affinity handle.