Medium and copy number effects on the secretion of human proinsulin in Escherichia coli using the universal stress promoters uspA and uspB

A genetic toolkit for co-expression of multiple proteins of diverse physiological implication

Construction of plasmids is crucial for expression of functional proteins of diverse physiological impact in E. coli. Here, we first designed and constructed a novel pair of bacterial expression vectors, i.e., pAS01 and pAS02, to be co-transformed with pQE30 for the co-expression of three target genes. The three plasmids contain ColE1, p15A and pSC101 origin of replication for high, medium and low copy plasmids, respectively, and same promoter (T5) and RBS. We then cloned genes encoding three reporter proteins (GFPuv, TurboRFP, and EYFP) in each of these plasmids and co-expressed in E. coli in six different combinations. Each of these reporter proteins exhibited diverse impact on growth, plasmid copy number and stability, and expression of other reporter proteins. Our results indicate that GFP and RFP were the most and the least favorable proteins for the cells, respectively, in terms of these parameters, especially on impacting expression of other co-expressed proteins.

Controlled functional expression of the bacteriocins pediocin PA-1 and bactofencin A in Escherichia coli

The bacteriocins bactofencin A (class IId) and pediocin PA-1 (class IIa) are encoded by operons with a similarly clustered gene organization including a structural peptide, an immunity protein, an ABC transporter and accessory bacteriocin transporter protein. Cloning of these operons in E. coli Tuner^TM (DE3) on a pETcoco-2 derived vector resulted in successful secretion of both bacteriocins. A corresponding approach, involving the construction of vectors containing different combinations of these genes, revealed that the structural and the transporter genes alone are sufficient to permit heterologous production and secretion in this host. Even though the accessory protein, usually associated with optimal disulfide bond formation, was not required for bacteriocin synthesis, its presence did result in greater pediocin PA-1 production. The simplicity of the system and the fact that the associated bacteriocins could be recovered from the extracellular medium provides an opportunity to facilitate protein engineering and the overproduction of biologically-active bacteriocins at industrial scale. Additionally, this system could enable the characterization of new bacteriocin operons where genetic tools are not available for the native producers.

Using folding promoting agents in recombinant protein production: a review

Recombinant production has become an invaluable tool for supplying research and therapy with proteins of interest. The target proteins are not in every case soluble and/or correctly folded. That is why different production parameters such as host, cultivation conditions and co-expression of chaperones and foldases are applied in order to yield functional recombinant protein. There has been a constant increase and success in the use of folding promoting agents in recombinant protein production. Recent cases are reviewed and discussed in this chapter. Any impact of such strategies cannot be predicted and has to be analyzed and optimized for the corresponding target protein. The in vivo effects of the agents are at least partially comparable to their in vitro mode of action and have been studied by means of modern systems approaches and even in combination with folding/activity screening assays. Resulting data can be used directly for experimental planning or can be fed into knowledge-based modelling. An overview of such technologies is included in the chapter in order to facilitate a decision about the potential in vivo use of folding promoting agents.

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.

Periplasmic expression and recovery of human interferon gamma in Escherichia coli

A synthetic human interferon gamma (hIFN-gamma) gene was fused to SP1 and SP3, two Sec-dependent artificial signal peptides to transport the hIFN-gamma to the periplasm of Escherichia coli BL21-SI. The processing efficiency of both SP1-hIFN-gamma and SP3-hIFN-gamma was dependent on the culture medium as well as the post-induction temperature. Both precursors were processed completely when cells were cultured using minimal medium and a post-induction temperature of 32.5 degrees C, and only the processed hIFN-gamma was detected. The SP3 signal peptide was more efficient than SP1 for the secretion of hIFN-gamma. Sixty percent of the total hIFN-gamma was secreted to the periplasm using the SP3 signal peptide and a post-induction temperature of 20 degrees C. Using Tris-sucrose-dithiothreitol (TSD) hypertonic buffer, the periplasmic soluble hINF-gamma was recovered with a purity of 85%.

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.

Engineering HlyA hypersecretion inEscherichia coli based on proteomic and microarray analyses

Escherichia coli is a common host for recombinant protein production for biotechnology applications. Secretion to the extracellular media has the potential to reduce protein aggregation and to simplify downstream purification. However, the complexity of the mechanisms of protein secretion has confounded prior attempts to engineer enhanced secretion phenotypes. Here, mutagenesis was used to perturb E. coli W3110 cells secreting HlyA via a Type I pathway. An activity assay identified a mutant secreting fourfold more active alpha-hemolysin than the parent strain. The mutant was characterized using both high-density microarrays for mRNA profiling and a proteomics strategy for protein expression. The relative mRNA and protein expression levels of tRNA-synthetases were decreased in the mutant compared to the parent. A mathematical model of prokaryotic translation was used to design a variant of the hlyA gene that encodes the same amino acid sequence but uses rare codons to slow the rate of translation by altering five bases. Analysis of the parent strain transformed with a plasmid containing this variant gene resulted in the recovery of, and further improvement upon, the selected hypersecretion phenotype. These results present one of the first successful metabolic engineering attempts based on molecular information provided by mRNA and protein expression profiling approaches and resulting in a phenotype useful to the biotechnology community.