Optimisation of signal peptide for recombinant protein secretion in bacterial hosts

Enhanced production of extracellular triacylglycerol lipase for bioplastic degradation by replacing signal peptide

With the increase in plastic production, efficient and timely plastic degradation are urgently needed. In that point, biodegradable plastics have attracted attention as potential solutions for environmental pollution of plastics. However, finding of superior degrading strains and enzymes such as esterase, cutinase, and triacylglycerol lipase (TGL) of bioplastic are still needed together with the efficient secretion systems of degrading enzymes. As a result, we investigated methods to enhance protein expression and secretion of novel bioplastic degrading enzyme by using signal peptides. The genes encoding TGL from Bacillus sp. JY35 and various secretory (Sec) pathway signal peptides were cloned together by replacing the original signal sequence, and they were expressed under T7 promoters in Escherichia coli BL21 (DE3). Esterase activity with p-nitrophenol esters, a plate assay, and SDS-PAGE were performed to screen and evaluate signal peptide efficiency. As a result, the PhoA-TGL combination was the most effective against bioplastic degradation, achieving a Polycaprolactone (PCL) degradation efficiency of 77 %, which was approximately 3.3 times higher than that of TGL with the original signal peptide. Furthermore, Polybutylene succinate (PBS) degradation under similar conditions was 1.5 times higher. Overall, this study showed signal peptide engineering could enhance the extracellular secretion and degradation system of triacylglycerol lipase (TGL) and highlights the potential of PhoA signal peptides and E. coli host to enhance production and secretion of plastic-degrading enzyme and degrading system.

An inverse relationship between fitness and secretion efficiency in a gram-positive bacterium

Lactiplantibacillus plantarum and other lactic acid bacteria are emerging as promising candidates for mucosal delivery of surface-displayed antigens. However, producing secreted heterologous proteins and anchoring these using LPxTG anchors can significantly reduce bacterial fitness. To understand the underlying mechanisms and limiting factors, we analyzed 11 recombinant L. plantarum strains expressing the HaloTag reporter protein with the same LPxTG anchor but varying signal peptides. By labeling the reporter protein with fluorescent ligands, this approach allowed simultaneous detection of correctly folded intracellular and extracellular protein, revealing signal peptide-dependent variation in the relative amounts of intra- and extracellularly folded HaloTag. Furthermore, this analysis uncovered an unexpected correlation between secretion efficiency and bacterial fitness. Strains with better growth showed more premature intracellular folding and reduced protein translocation and surface display. Conversely, strains with a higher fraction of surface-displayed protein, i.e. strains with greater secretion efficiency, exhibited impaired growth, likely due to increased interactions between the signal peptide and the secretion machinery, leading to secretion overload. Correlation analyses and confirmation of observed correlations by mutational studies of the signal peptides showed that signal peptide hydrophobicity is positively correlated with higher secretion efficiency but is accompanied by a trade-off in fitness. These findings underscore the critical role of signal peptides in balancing protein secretion and bacterial viability, offering valuable insights for optimizing protein secretion and anchoring in gram-positive bacteria.

HNP-1: From Structure to Application Thanks to Multifaceted Functions

Antimicrobial peptides (AMPs) are critical components of innate immunity in animals and plants, exhibiting thrilling prospectives as alternatives to traditional antibiotics due to their ability to combat pathogens without leading to resistance. Among these, Human Neutrophil Peptide-1 (HNP-1), primarily produced by human neutrophils, exhibits broad-spectrum antimicrobial activity against bacteria and viruses. However, the clinical application of HNP-1 has been hampered by challenges associated with mass production and inconsistent understanding of its bactericidal mechanisms. This review explores the structure and function of HNP-1, discussing its gene expression, distribution, immune functions and the regulatory elements controlling its production, alongside insights into its antimicrobial mechanisms and potential clinical applications as an antimicrobial agent. Furthermore, the review highlights the biosynthesis of HNP-1 using microbial systems as a cost-effective alternative to human extraction and recent studies revealing HNP-1's endogenous bactericidal mechanism. A comprehensive understanding of HNP-1's working mechanisms and production methods will pave the way for its effective clinical utilization in combating antibiotic-resistant infections.

Resonance assignments of cytochrome MtoD from the extracellular electron uptake pathway of sideroxydans lithotrophicus ES-1

The contribution of Fe(II)-oxidizing bacteria to iron cycling in freshwater, groundwater, and marine environments has been widely recognized in recent years. These organisms perform extracellular electron transfer (EET), which constitutes the foundations of bioelectrochemical systems for the production of biofuels and bioenergy. It was proposed that the Gram-negative bacterium Sideroxydans lithotrophicus ES-1 oxidizes soluble ferrous Fe(II) at the surface of the cell and performs EET through the Mto redox pathway. This pathway is composed by the periplasmic monoheme cytochrome MtoD that is proposed to bridge electron transfer between the cell exterior and the cytoplasm. This makes its functional and structural characterization, as well as evaluating the interaction process with its physiological partners, essential for understanding the mechanisms underlying EET. Here, we report the complete assignment of the heme proton and carbon signals together with a near-complete assignment of 1H, 13C and 15N backbone and side chain resonances for the reduced, diamagnetic form of the protein. These data pave the way to identify and structurally map the molecular interaction regions between the cytochrome MtoD and its physiological redox partners, to explore the EET processes of S. lithotrophicus ES-1.

Heterologous protein exposure and secretion optimization in Mycoplasma pneumoniae

The non-pathogenic Mycoplasma pneumoniae engineered chassis (Mycochassis) has demonstrated the ability to express therapeutic molecules in vitro and to be effective for treatment of lung infectious diseases in in vivo mouse models. However, the expression of heterologous molecules, whether secreted or exposed on the bacterial membrane has not been optimized to ensure sufficient secretion and/or exposure levels to exert a maximum in vivo biological effect. Here, we have improved the currently used secretion signal from MPN142 protein. We found that mutations at P1' position of the signal peptide cleavage site do not abrogate secretion but affect it. Increasing hydrophobicity and mutations at the C-terminal of the signal peptide increases secretion. We tested different lipoprotein signal peptides as possible N-terminal protein anchoring motifs on the Mpn cell surface. Unexpectedly we found that these peptides exhibit variable retention and secretion rates of the protein, with some sequences behaving as full secretion motifs. This raises the question of the biological role of the lipobox motif traditionally thought to anchor membrane proteins without a helical transmembrane domain. These results altogether represent a step forward in chassis optimization, offering different sequences for secretion or membrane retention, which could be used to improve Mycochassis as a delivery vector, and broadening its therapeutic possibilities.

Extracellular production of azurin by reusable magnetic Fe3O4 nanoparticle-immobilized Pseudomonas aeruginosa

Azurin, found in the periplasm of Pseudomonas aeruginosa, has garnered significant attention as a potential anticancer agent in recent years. High-level secretion of proteins into the culture medium, offers a significant advantage over periplasmic or cytoplasmic expression. In this study, for the first time, P. aeruginosa cells were immobilized with magnetic nanoparticles (MNPs) to ensure effective, simple and quick separation of the cells and secretion of periplasmic azurin protein to the culture medium. For this purpose, polyethyleneimine-coated iron oxide (Fe3O4@PEI) MNPs were synthesized and MNPs containing Fe up to 600 ppm were found to be non-toxic to the bacteria. The highest extracellular azurin level was observed in LB medium compared to peptone water. The cells immobilized with 400 ppm Fe-containing MNPs secreted the highest protein. Lastly, the immobilized cells were found suitable for azurin secretion until the sixth use. Thus, the magnetic nanoparticle immobilization method facilitated the release of azurin as well as the simple and rapid separation of cells. This approach, by facilitating protein purification and enabling the reuse of immobilized cells, offers a cost-effective means of protein production, reducing waste cell formation, and thus presents an advantageous method.

Comparison of the efficiency of the Sec and Tat secretory pathways in the secretion of recombinant neurturin protein using de novo designed signal peptides

Since cytoplasmic expression of heterologous proteins with disulfide bonds leads to the formation of inclusion bodies in E. coli, periplasmic production is preferable. The N-terminal signal peptide attached to the secreted protein determines the type of secretory pathway through which the target protein is secreted; Sec, Tat, or SRP. The aim of this study was to design and compare two novel signal peptides for the secretion of recombinant neurturin (as a model) via the Sec and Tat pathways. For this purpose, we aligned the natural signal peptides from E. coli and Bacillus subtilis to identify the conserved amino acids and those with the highest repetition. The SignalP4.1 and TatP1.0 software were used to determine the secretion efficiency of the new signal peptides. The efficiency of new signal peptides was then evaluated and compared experimentally with two naturally used signal peptides. Quantitative analysis of Western blot bands showed that approximately 80% of the expressed neurturin was secreted into the periplasmic space by new signal peptides. Circular dichroism spectroscopy also confirmed the correct secondary structure of the secreted neurturin. In conclusion, these novel signal peptides can be used to secrete any other recombinant proteins to the periplasmic space of E. coli efficiently.

Degradation of polyethylene terephthalate (PET) plastics by wastewater bacteria engineered via conjugation

Wastewater treatment plants are one of the major pathways for microplastics to enter the environment. In general, microplastics are contaminants of global concern that pose risks to ecosystems and human health. Here, we present a proof-of-concept for reduction of microplastic pollution emitted from wastewater treatment plants: delivery of recombinant DNA to bacteria in wastewater to enable degradation of polyethylene terephthalate (PET). Using a broad-host-range conjugative plasmid, we enabled various bacterial species from a municipal wastewater sample to express FAST-PETase, which was released into the extracellular environment. We found that FAST-PETase purified from some transconjugant isolates could degrade about 40% of a 0.25 mm thick commercial PET film within 4 days at 50°C. We then demonstrated partial degradation of a post-consumer PET product over 5-7 days by exposure to conditioned media from isolates. These results have broad implications for addressing the global plastic pollution problem by enabling environmental bacteria to degrade PET.

Molecular strategies to enhance the keratinase gene expression and its potential implications in poultry feed industry

The tons of keratin waste are produced by the poultry and meat industry which is an insoluble and protein-rich material found in hair, feathers, wool, and some epidermal wastes. These waste products could be degraded and recycled to recover protein, which can save our environment. One of the potential strategy to achieve this target is use of microbial biotreatment which is more convenient, cost-effective, and environment-friendly by formulating hydrolysate complexes that could be administered as protein supplements, bioactive peptides, or animal feed ingredients. Keratin degradation shows great promise for long-term protein and amino acid recycling. According to the MEROPS database, known keratinolytic enzymes currently belong to at least 14 different protease families, including S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, and M55. In addition to exogenous attack (proteases from families S9, S10, M14, M28, M38, and M55), the various keratinolytic enzymes also function via endo-attack (proteases from families S1, S8, S16, M4, M16, and M36). Biotechnological methods have shown great promise for enhancing keratinase expression in different strains of microbes and different protein engineering techniques in genetically modified microbes such as bacteria and some fungi to enhance keratinase production and activity. Some microbes produce specific keratinolytic enzymes that can effectively degrade keratin substrates. Keratinases have been successfully used in the leather, textile, and pharmaceutical industries. However, the production and efficiency of existing enzymes need to be optimized before they can be used more widely in other processes, such as the cost-effective pretreatment of chicken waste. These can be improved more effectively by using various biotechnological applications which could serve as the best and novel approach for recycling and degrading biomass. This paper provides practical insights about molecular strategies to enhance keratinase expression to effectively utilize various poultry wastes like feathers and feed ingredients like soybean pulp. Furthermore, it describes the future implications of engineered keratinases for environment friendly utilization of wastes and crop byproducts for their better use in the poultry feed industry.

An ovalbumin fusion strategy to increase recombinant protein secretion in chicken eggs

Maternal secretion of recombinant proteins into chicken eggs may provide a viable approach for pharmaceutical production but remains limited by poor secretion efficiency through the membrane of oviduct cells, despite high expression levels. Here, we used site-specific integration of an EGFP fused to the OVAL gene by a rigid linker, (EAAAK)3, at the endogenous ovalbumin locus in chicken primordial germ cells to generate OVAL-E3-EGFP transgenic chickens, with transgenic chickens expressing CMV immediate enhancer/β-actin-driven EGFP (CAG-EGFP) as a non-secreted control. In OVAL-E3-EGFP chickens, EGFP protein produced in maternal oviducts accumulates to high levels in eggs, but not in eggs of CAG-EGFP chickens. These results indicated that the secretion of foreign proteins can be substantially increased through fusion to the highly secreted endogenous ovalbumin. This study describes a basis for high yield recombinant protein expression in chicken eggs, enabling rapid and scalable production of numerous pharmaceutical proteins or metabolites.

Enhancing the heterologous expression of latex clearing protein from Streptomyces sp. strain K30 in Escherichia coli through fermentation condition optimization and molecular modification

Latex clearing protein from Streptomyces sp. strain K30 (LcpK30) is a natural oxidoreductase that can catalyse the cleavage of rubber through dioxygenation. It has significant potential applications in polymer degradation. However, its limited expression in engineered strains restricts its utility. This study aimed to enhance the soluble expression and enzyme activity of LcpK30 in E. coli BL21 (DE3) by optimizing fermentation conditions and making molecular modifications. The enzyme activity reached 5.05 U·mL-1 by optimizing the induction conditions, adding cofactors, and using chemical chaperones, which was 237.1 % of the initial case. Further enhancements in soluble expression were achieved through site mutations guided by the PROSS server, resulting in 8 out of 13 mutants with increased protein expression, a high positive mutation rate of 61.5 %. Subsequently, combined mutants were created by merging single mutants with enhanced protein expression and enzyme activity. The top three double mutants, G91D/S149A, G91D/A210H, and G91D/H296P, displayed expression levels at 173.3 %, 173.3 %, and 153.3 % of the wild-type LcpK30, respectively. These mutants also exhibited enhanced fermentation enzyme activity, reaching 149.5 %, 250.0 %, and 420.2 % compared to the wild-type, along with improved specific activities. This study provides insights for the efficient production of LcpK30 and a practical foundation for its application.

Approaches for high-throughput quantification of periplasmic recombinant proteins

The Gram-negative periplasm is a convenient location for the accumulation of many recombinant proteins including biopharmaceutical products. It is the site of disulphide bond formation, required by some proteins (such as antibody fragments) for correct folding and function. It also permits simpler protein release and downstream processing than cytoplasmic accumulation. As such, targeting of recombinant proteins to the E. coli periplasm is a key strategy in biologic manufacture. However, expression and translocation of each recombinant protein requires optimisation including selection of the best signal peptide and growth and production conditions. Traditional methods require separation and analysis of protein compositions of periplasmic and cytoplasmic fractions, a time- and labour-intensive method that is difficult to parallelise. Therefore, approaches for high throughput quantification of periplasmic protein accumulation offer advantages in rapid process development.

Development of Heterologous Expression System and Optimization of the Method of Cholera Toxin β-Subunit Production in E. coli

Cholera is a deadly infection disease, which is usually associated with low hygiene levels and limited access to high-quality drinking water. An effective way to prevent cholera is the use of vaccines. Among active vaccine components there is the CtxB protein (cholera toxin β-subunit). In the current work, we have developed a genetic system for production of the recombinant CtxB in E. coli cells and studied conditions for synthesis and purification of the target product at the laboratory scale. It has been found that the optimal algorithm for isolation of the recombinant protein is to grow E. coli culture in the synthetic M9 medium with glycerol, followed by CtxB purification out of the spent culture medium using Ni2+-chelate affinity chromatography techniques. Forty-eight hours after induction of CtxB expression, concentration of the target product could be up to 50 mg/liter in the culture medium. The CtxB protein retains its pentameric structure during expression and through purification. The latter makes it possible to consider the developed system as a promising tool for the industrial-level production of recombinant CtxB for medical and research purposes.

Extracellular Expression of Feruloyl Esterase and Xylanase in Escherichia coli for Ferulic Acid Production from Agricultural Residues

There is still a large amount of ferulic acid (FA), an outstanding antioxidant, present in agricultural residues. Enzymatic hydrolysis has been regarded as the most effective way to release FA. This present study therefore selected feruloyl esterase (FAE) and xylanase (XYN) from the metagenomes of a cow rumen and a camel rumen, respectively, for their recombinant expression in Escherichia coli BL21 and further application in releasing FA. After screening the candidate signal peptides, the optimal one for each enzyme, which were selected as SP1 and SP4, respectively, was integrated into the vectors pET22b(+) and pETDuet-1. Among the generated E. coli strains SP1-F, SP4-X, and SP1-F-SP4-X that could express extracellular enzymes either separately or simultaneously, the latter one performed the best in relation to degrading the biomass and releasing FA. Under the optimized culture and induction conditions, the strain SP1-F-SP4-X released 90% of FA from 10% of de-starched wheat bran and produced 314.1 mg/L FA, which was deemed to be the highest obtained value to the best of our knowledge. This result could pave a way for the re-utilization of agricultural residues and enhancing their add-value.

Microbial nattokinase: from synthesis to potential application

Nattokinase (NK) is an alkaline serine protease with strong thrombolytic activity produced by Bacillus spp. or Pseudomonas spp. It is a potential therapeutic agent for thrombotic diseases because of its safety, economy, and lack of side effects. Herein, a comprehensive summary and analysis of the reports surrounding NK were presented, and the physical-chemical properties and producers of NK were first described. The process and mechanism of NK synthesis were summarized, but these are vague and not specific enough. Further results may be achieved if detection techniques such as multi-omics are used to explore the process of NK synthesis. The purification of NK has problems such as a complicated operation and low recovery rate, which were found when summarizing the techniques to improve the quality of finished products. If multiple simple and efficient precipitation methods and purification materials are combined to purify NK, it may be possible to solve the current challenges. Additionally, the application potential of NK in biomedicine was reviewed, but functional foods with NK are challenging for acceptance in daily life due to their unpleasant odor. Accordingly, multi-strain combination fermentation or food flavoring agents can improve the odor of fermented foods and increase people's acceptance of them. Finally, the possible future directions focused on NK studies were proposed and provided suggestions for subsequent researchers.

Optimized Signal Peptide for Secretory Expression of Human Recombinant Somatropin in E. coli

Purpose: The human somatropin is a single-chain polypeptide with a pivotal role in various biological processes. Although Escherichia coli is considered as a preferred host for the production of human somatropin, the high expression of this protein in E. coli results in the accumulation of protein as inclusion bodies. Periplasmic expression using signal peptides could be used to overcome the formation of inclusion bodies; still, the efficiency of each of the signal peptides in periplasmic transportation is varied and often is protein specific. The present study aimed to use in silico analysis to identify an appropriate signal peptide for the periplasmic expression of human somatropin in E. coli. Methods: A library containing 90 prokaryotic and eukaryotic signal peptides were collected from the signal peptide database, and each signal's characteristics and efficiency in connection with the target protein were analyzed by different software. The prediction of the secretory pathway and the cleavage position was determined by the signalP5 server. Physicochemical properties, including molecular weight, instability index, gravity, and aliphatic index, were investigated by ProtParam software. Results: The results of the present study showed that among all the signal peptides studied, five signal peptides ynfB, sfaS, lolA, glnH, and malE displayed high scores for periplasmic expression of human somatropin in E. coli, respectively. Conclusion: In conclusion, the results indicated that in-silico analysis could be used for the identification of suitable signal peptides for the periplasmic expression of proteins. Further laboratory studies can evaluate the accuracy of the results of in silico analysis.

Development of stable HEK293T cell pools expressing CSFV E2 protein: A potential antigen expression platform

Large quantities of antigens are required since protective antigens, such as classical swine fever virus (CSFV) E2 protein, are widely used in diagnostic reagents and subunit vaccines. Compared to clonal cell lines and transient gene expression, stable cell pools provide a potential alternative platform to rapidly produce large amounts of antigens. In this work, firstly, Human embryonic kidney 293 T (HEK293T) cell pools expressing E2 protein were developed by transduction of lentiviral vectors. On the one hand, the SP7 was selected from 7 well-performing signal peptides to remarkably increase the production of E2 protein. On the other hand, it was found that high MOI could improve the expression of E2 protein by increasing gene copy numbers. Moreover, the HEK293T cell pools were evaluated for stability by passages and batch cultures, demonstrating that the cell pools were stable for at least 90 days. And then, the performance of the cell pools in batch, fed-batch, and semi-perfusion was studied. Among them, the titer of E2 protein was up to 2 g/L in semi-perfusion, which is currently the highest to the authors' knowledge. Finally, the aggregations and immunogenicity of the E2 protein were analyzed by SDS-PAGE and immunization of mice, respectively. There was no significant difference in aggregations and antibody titers of E2 protein in three culture methods. These results suggest that stable HEK293T cell pools are a promising and robust platform for rapid and efficient production of recombinant proteins.

N-region of Cry1Ia: A novel fusion tag for Escherichia coli and Pichia pastoris

Secretory signal peptides (SPs) can increase enhanced green fluorescent protein (eGFP) expression in cytosol. In this study, SPs Iasp (Cry1Ia), Vasp (Vip3A), and their local sequences were used as fusion tags to compare their effects on eGFP expression in Escherichia coli MC4100 and Pichia pastoris GS115. In E coli, the solubility was almost opposite between the proteins encoded by Vegfp and Iegfp. This may be because the overall hydrophobicity of the SPs differed. When the hydrophobic H-region and C-region were removed, the negative effects on eGFP solubility of the N-regions of both SPs (IaN and VN) were significantly reduced without compromise on the expression level. IaN promotes eGFP protein yield 7.1-fold more than Iasp, and using this peptide in tandem (Ia3N) further enhanced fluorescent fusion protein solubility with an efficacy similar to that of a polycationic tag. Furthermore, the GS-IaNeGFP strain produced the highest fluorescent signal intensity when these fusion proteins were expressed in P. pastoris, and the expression was higher than in other strains, including eGFP. In conclusion, we revealed the potential of the N-region of Iasp as a fusion tag in both prokaryotic and eukaryotic cells and further demonstrated the value of the N-regions of abundant SPs.

Generation of Proteins with Free N-Terminal Cysteine by Aminopeptidases

Efficient, site-specific, and bio-orthogonal conjugation of chemical functionalities to proteins is of great utility in fundamental research as well as industrial processes (e.g., the production of antibody-drug conjugates and immobilization of enzymes for biocatalysis). A popular approach involves reacting a free N-terminal cysteine with a variety of electrophilic reagents. However, current methods for generating proteins with N-terminal cysteines have significant limitations. Herein we report a novel, efficient, and convenient method for producing recombinant proteins with free N-terminal cysteines by genetically fusing a Met-Pro-Cys sequence to the N-terminus of a protein of interest and subjecting the recombinant protein to the sequential action of methionine and proline aminopeptidases. The resulting protein was site-specifically labeled at the N-terminus with fluorescein and a cyclic cell-penetrating peptide through native chemical ligation and a 2-cyanobenzothiazole moiety, respectively. In addition, the optimal recognition sequence of Aeromonas sobria proline aminopeptidase was determined by screening a combinatorial peptide library and incorporated into the N-terminus of a protein of interest for most efficient N-terminal processing.

Increasing the Efficiency of the Accumulation of Recombinant Proteins in Plant Cells: The Role of Transport Signal Peptides

The problem with increasing the yield of recombinant proteins is resolvable using different approaches, including the transport of a target protein to cell compartments with a low protease activity. In the cell, protein targeting involves short-signal peptide sequences recognized by intracellular protein transport systems. The main systems of the protein transport across membranes of the endoplasmic reticulum and endosymbiotic organelles are reviewed here, as are the major types and structure of the signal sequences targeting proteins to the endoplasmic reticulum and its derivatives, to plastids, and to mitochondria. The role of protein targeting to certain cell organelles depending on specific features of recombinant proteins and the effect of this targeting on the protein yield are discussed, in addition to the main directions of the search for signal sequences based on their primary structure. This knowledge makes it possible not only to predict a protein localization in the cell but also to reveal the most efficient sequences with potential biotechnological utility.

Designing a novel fusion protein from Streptococcus agalactiae with apoptosis induction effects on cervical cancer cells

Cervical cancer remains life-threatening cancer in women around the world. Due to the limitations of conventional treatment approaches, there is an urgent need to develop novel and more efficient strategies against cervical cancer. Therefore, the researchers attend to the alternative anti-cancer compounds like bacterial products. Rib and α are known as surface proteins of Streptococcus agalactiae with immunologic effects. In the present study, we designed a new anti-cancer fusion protein (Rib-α) originating from S. agalactiae with in silico methods, and then, the recombinant gene was cloned in the pET-22 (+) expression vector. The recombinant protein was expressed in E. coli BL21. To purify the expressed protein, we applied the Ni-NTA column. The molecular mechanism by which Rib-α is cytotoxic to cancer cells has been discussed based on MTT, flow cytometry, and real-time PCR methods. The engineered fusion protein suppressed the proliferation of the cancer cells at 180 μg/ml. Cytotoxic assessment and morphological changes, augmentation of apoptotic-related genes, upregulation of caspase-3 mRNA, and flow cytometric analysis confirmed that apoptosis might be the principal mechanism of cell death. According to our findings, Rib-α fusion protein motivated the intrinsic apoptosis pathway. Therefore, it can be an exciting candidate to discover a new class of antineoplastic agents.

Expression and characterization of hemagglutinin-neuraminidase protein from Newcastle disease virus in Bacillus subtilis WB800

Background

Newcastle disease virus (NDV) belongs to the genus Avaluvirus and Paramyxoviridae family, and it can cause acute, highly contagious Newcastle disease in poultry. The two proteins, haemagglutinin neuraminidase (HN) and Fusion (F), are the main virulence factor of the virus and play an essential role in immunogenicity against the virus. In most paramyxoviruses, the F protein requires HN protein to fuse the membrane, and HN proteins substantially enhance the viruses’ fusion activity.

Results

The present study describes the successful cloning and expression of HN protein from NDV in Bacillus subtilis WB800 using the modified shuttle vector pHT43. HN coding sequence was cloned into the pGet II vector. It was then subcloned into the PHT43 shuttle vector and transferred to Escherichia coli for replication. The recombinant plasmid was extracted from E. coli and used to transform B. subtilis by electroporation. After induction of recombinant B. subtilis by IPTG, total cell protein and the protein secreted into the media were analysed through a time course using SDS-PAGE. The expressed HN protein was purified using cation exchange chromatography followed by metal affinity chromatography, using the 6× His epitope introduced at the carboxyl terminus of the recombinant protein. The accuracy of the PHT43-HN construct was confirmed by sequencing and enzymatic digestion. SDS-PAGE results showed that the recombinant HN protein was successfully expressed and secreted into the medium. Moreover, the purified HN protein showed neuraminidase activity with characteristics similar to the indigenous HN NDV protein. B. subtilis is a free endotoxin host that could be a favourite prokaryotic platform for producing the recombinant HN protein.

Conclusion

The establishment of this expression and purification system has allowed us to explore further the biochemical characteristics of HN protein and obtain material that could be suitable for a new production of NDV candidate vaccine with high immunogenicity.

Engineering multifunctional enzymes for agro-biomass utilization

Lignocellulosic biomass is a plentiful renewable resource that can be converted into a wide range of high-value-added industrial products. However, the complexity of its structural integrity is one of the major constraints and requires combinations of different fibrolytic enzymes for the cost-effective, industrially and environmentally feasible transformation. An interesting approach is constructing multifunctional enzymes, either in a single polypeptide or by joining multiple domains with linkers and performing diverse reactions simultaneously, in a single host. The production of such chimera proteins multiplies the advantages of different enzymatic reactions in a single setup, in lesser time, at lower production cost and with desirable and improved catalytic activities. This review embodies the various domain-tailoring and extracellular secretion strategies, possible solutions to their challenges, and efforts to experimentally connect different catalytic activities in a single host, as well as their applications.

Extracellular production of azurin from Pseudomonas aeruginosa in the presence of Triton X-100 or Tween 80

Azurin which is a bacterial secondary metabolite has attracted much attention as potential anticancer agent in recent years. This copper-containing periplasmic redox protein supresses the tumor growth selectively. High-level secretion of proteins into the culture medium offers a significant advantage over periplasmic or cytoplasmic expression. The aim of this study was to investigate the effect of nonionic surfactants on the expression of the Pseudomonas aeruginosa azurin. Different concentrations of Triton X-100 and Tween 80 were used as supplements in growth media and extracellular azurin production was stimulated by both surfactants. According to western blot analysis results, in the presence of Triton X-100, maximum azurin expression level was achieved with 96 h of incubation at 1% concentration, and 48 h at 2% concentration. On the other hand, maximum azurin expression level was achieved in the presence of 1% Tween 80 at 72 h incubation. This study suggested for the first time a high level of azurin secretion from P. aeruginosa in the presence of Triton X-100 or Tween 80, which would be advantageous for the purification procedure.

Rahman RNZ, Tan JS, Raja Khairuddin RF, Salleh AB, Oslan SN. Determination of Putative Vacuolar Proteases, PEP4 and PRB1 in a Novel Yeast Expression Host Meyerozyma guilliermondii Strain SO Using Bioinformatics Tools

Meyerozyma guilliermondii strain SO, a newly isolated yeast species from spoilt orange, has been used as a host to express the recombinant proteins using methylotrophic yeast promoters. However, as a novel yeast expression system, the vacuolar proteases of this yeast have not been determined, which may have contributed to the low level of heterologous protein secretions. Thus, this study aimed to determine intra- and extracellular proteolytic activity and identify the putative vacuolar proteases using bioinformatics techniques. A clear zone was observed from the nutrient agar skimmed milk screening plate. Proteolytic activity of 117.30 U/ml and 75 U/ml were obtained after 72 h of cultivation for both extracellular and intracellular proteins, respectively. Next, the Hidden Markov model (HMM) was used to detect the presence of the vacuolar proteases (PEP4 and PRB1) from the strain SO proteome. Aspartyl protease (PEP4) with 97.55% identity to Meyerozyma sp. JA9 and a serine protease (PRB1) with 70.91% identity to Candida albicans were revealed. The homology with other yeast vacuolar proteases was confirmed via evolutionary analysis. PROSPER tool prediction of cleavage sites postulated that PEP4 and PRB1 might have caused proteolysis of heterologous proteins in strain SO. In conclusion, two putative vacuolar proteases (PEP4 and PRB1) were successfully identified in strain SO. Further characterization can be done to understand their specific properties, and their effects on heterologous protein expression can be conducted via genome editing.

Finding Appropriate Signal Peptides for Secretory Production of Recombinant Glucarpidase: An In SilicoMethod

BACKGROUND

Methotrexate (MTX) is a general chemotherapeutic agent utilized to treat a variety of malignancies, woefully, its high doses can cause nephrotoxicity and subsequent defect in the process of MTX excretion. The recombinant form of glucarpidase is produced by engineered E. coli and is a confirmed choice to overcoming this problem.

OBJECTIVE

In the present study, in silico analyses were performed to select suitable SPs for the secretion of recombinant glucarpidase in E. coli.

METHODS

The signal peptide website and UniProt database were employed to collect the SPs and protein sequences. In the next step, SignalP-5.0 helped us to predict the SPs and the position of cleavage sites. Moreover, physicochemical properties and solubility were evaluated using Prot- Param and Protein-sol online software, and finally, ProtCompB was used to predict the final subcellular localization.

RESULTS

Luckily, all SPs could form soluble fusion proteins. At last, it was found that PPB and TIBA could translocate the glucarpidase into the extracellular compartment.

CONCLUSION

This study showed that there are only 2 applicable SPs for the extracellular translocation of glucarpidase. Although the findings were remarkable with high degrees of accuracy and precision based on the utilization of bioinformatics analyses, additional experimental assessments are required to confirm and validate it. Recent patents revealed several inventions related to the clinical aspects of vaccine peptides against human disorders.

In Silico Investigation of Signal Peptide Sequences to Enhance Secretion of CD44 Nanobodies Expressed in Escherichia coli

BACKGROUND

The selection of a suitable signal peptide that can direct recombinant proteins from the cytoplasm to the extracellular space is an important criterion affecting the production of recombinant proteins in Escherichia coli, a widely used host. Nanobodies are currently attracting the attention of scientists as antibody alternatives due to their specific properties and feasibility of production in E. coli.

OBJECTIVE

CD44 nanobodies constitute a potent therapeutic agent that can block CD44/HA interaction in cancer and inflammatory diseases. This molecule may also function as a drug against cancer cells and has been produced previously in E. coli without a signal peptide sequence. The goal of this project was to find a suitable signal peptide to direct CD44 nanobody extracellular secretion in E. coli that will potentially lead to optimization of experimental methods and facilitate downstream steps such as purification.

METHODS

We analyzed 40 E. coli derived signal peptides retrieved from the Signal Peptide database and selected the best candidate signal peptides according to relevant criteria including signal peptide probability, stability, and physicochemical features, which were evaluated using signalP software version 4.1 and the ProtParam tool, respectively.

RESULTS

In this in silico study, suitable candidate signal peptide(s) for CD44 nanobody secretory expression were identified. CSGA, TRBC, YTFQ, NIKA, and DGAL were selected as appropriate signal peptides with acceptable D-scores, and appropriate physicochemical and structural properties. Following further analysis, TRBC was selected as the best signal peptide to direct CD44 nanobody expression to the extracellular space of E. coli.

CONCLUSION

The selected signal peptide, TRBC is the most suitable to promote high-level secretory production of CD44 nanobodies in E. coli and potentially will be useful for scaling up CD44 nanobody production in experimental research as well as in other CD44 nanobody applications. However, experimental work is needed to confirm the data.

Enhanced Extracellular Production of IsPETase in Escherichia coli via Engineering of the pelB Signal Peptide

Poly(ethylene terephthalate) (PET) is one of the most commonly used plastics worldwide and its accumulation in the environment is a global problem. PETase from Ideonella sakaiensis 201-F6 was reported to exhibit higher hydrolytic activity and specificity for PET than other enzymes at ambient temperature. Enzymatic degradation of PET using PETase provides an attractive approach for plastic degradation and recycling. In this work, extracellular PETase was achieved by Escherichia coli BL21 using a Sec-dependent translocation signal peptide, pelB, for secretion. Furthermore, engineering of the pelB through random mutagenesis and screening was performed to improve the secretion efficiency of PETase. Evolved pelB enabled higher PETase secretion by up to 1.7-fold. The improved secretion of PETase led to more efficient hydrolysis of the PET model compound, bis (2-hydroxyethyl) terephthalic acid (BHET), PET powder, and PET film. Our study presents the first example of the increasing secretion of PETase by an engineered signal peptide, providing a promising approach to obtain extracellular PETase for efficient enzymatic degradation of PET.

Engineering Halomonas bluephagenesis as a chassis for bioproduction from starch

Halomonas bluephagenesis has been successfully engineered to produce multiple products under open unsterile conditions utilizing costly glucose as the carbon source. It would be highly interesting to investigate if H. bluephagenesis, a chassis for the Next Generation Industrial Biotechnology (NGIB), can be reconstructed to become an extracellular hydrolytic enzyme producer replacing traditional enzyme producer Bacillus spp. If successful, cost of bulk hydrolytic enzymes such as amylase and protease, can be significantly reduced due to the contamination resistant and robust growth of H. bluephagenesis. This also allows H. bluephagenesis to be able to grow on low cost substrates such as starch. The modularized secretion machinery was constructed and fine-tuned in H. bluephagenesis using codon-optimized gene encoding α-amylase from Bacillus lichenifomis. Screening of suitable signal peptides and linkers based on super-fold green fluorescence protein (sfGFP) for enhanced expression in H. bluephagenesis resulted in a 7-fold enhancement of sfGFP secretion in the recombinant H. bluephagenesis. When the gene encoding sfGFP was replaced by α-amylase encoding gene, recombinant H. bluephagenesis harboring this amylase secretory system was able to produce poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), ectoine and L-threonine utilizing starch as the growth substrate, respectively. Recombinant H. bluephagenesis TN04 expressing genes encoding α-amylase and glucosidase on chromosome and plasmid-based systems, respectively, was able to grow on corn starch to approximately 10 g/L cell dry weight containing 51% PHB when grown in shake flasks. H. bluephagenesis was demonstrated to be a chassis for productions of extracellular enzymes and multiple products from low cost corn starch.

Rational design of signal peptides for improved MtC1LPMO production in Bacillus amyloliquefaciens

A high-throughput screening system was established by employing enhanced green fluorescent protein as a screenable fusion tag to evaluate the expression and secretion of a lytic polysaccharide monooxygenase (MtC1LPMO) using 20 Sec-type signal peptides (SPs) from Bacillus amyloliquefaciens 111018. Among these, 10 SPs were found to be better than the native SP of MtC1LPMO. The protein expression and secretion levels using SP12 (MNITNWAAILQLQSMALQSISNTGTASS) were the highest among all SPs, with 4.1- and 2.1-fold increases over the native SP, respectively. Then, the amino acids of the 10 best SPs were analyzed, and the results indicated that the most abundant amino acid of the N-region was K, those of the H-region were L, F, A and V, and the C-region contained an AXA motif. Additionally, we found that the protein expression level gradually improved along with the increasing folding free energies of the SP-encoding part of the mRNA. Finally, the SPs were rationally designed to improve the expression and secretion level of MtC1LPMO. An increased positive charge of the SP N-region was found to enhance the protein expression and secretion level, as long as the folding free energy of the mRNA did not change significantly.

Discovering and efficiently promoting the extracellular secretory expression of Thermobacillus sp. ZCTH02-B1 sucrose phosphorylase in Escherichia coli

Sucrose phosphorylase (SPase, EC2.4.1.7) is a promising transglycosylation biocatalyst used for producing glycosylated compounds that are widely used in the food, cosmetics, and pharmaceutical industries. In this study, a recombinant SPase from the Thermobacillus sp. ZCTH02-B1 (rTSPase), which was previously reported to have high thermostability and the catalytic ability to synthesize ascorbic acid 2-glucoside, was attempted to be extracellularly expressed in Escherichia coli BL21(DE3) by fusion of endogenous osmotically-inducible protein Y. Unexpectedly, the rTSPase itself was produced outside the cells with an underestimated performance, although no typical signal peptide was predicted. Further N- and C-terminal truncation experiments revealed that both termini of rTSPase have an important role in protein folding and enzymatic activity, while its secretion was N-terminus associated. Extracellular protein concentration and rTSPase activity achieved 1.8 mg/mL and 6.2 U/mL after induction of 36 h in a 5-L fermenter. High-level extracellular rTSPase production could also be obtained from E. coli within 24 h by inducing overexpression of D, D-carboxypeptidase for cell lysis.

Evolution of Escherichia coli Expression System in Producing Antibody Recombinant Fragments

Antibodies and antibody-derived molecules are continuously developed as both therapeutic agents and key reagents for advanced diagnostic investigations. Their application in these fields has indeed greatly expanded the demand of these molecules and the need for their production in high yield and purity. While full-length antibodies require mammalian expression systems due to the occurrence of functionally and structurally important glycosylations, most antibody fragments and antibody-like molecules are non-glycosylated and can be more conveniently prepared in E. coli-based expression platforms. We propose here an updated survey of the most effective and appropriate methods of preparation of antibody fragments that exploit E. coli as an expression background and review the pros and cons of the different platforms available today. Around 250 references accompany and complete the review together with some lists of the most important new antibody-like molecules that are on the market or are being developed as new biotherapeutics or diagnostic agents.

Signal Peptides Generated by Attention-Based Neural Networks

Short (15-30 residue) chains of amino acids at the amino termini of expressed proteins known as signal peptides (SPs) specify secretion in living cells. We trained an attention-based neural network, the Transformer model, on data from all available organisms in Swiss-Prot to generate SP sequences. Experimental testing demonstrates that the model-generated SPs are functional: when appended to enzymes expressed in an industrial Bacillus subtilis strain, the SPs lead to secreted activity that is competitive with industrially used SPs. Additionally, the model-generated SPs are diverse in sequence, sharing as little as 58% sequence identity to the closest known native signal peptide and 73% ± 9% on average.

N-Terminal Fused Signal Peptide Prompted Extracellular Production of a Bacillus-Derived Alkaline and Thermo Stable Xylanase in E. coli Through Cell Autolysis

Xylanases are extensively used as industrial enzymes for its ability of hydrolyzing xylan to oligosaccharides. Here, XynHB, a thermo and alkaline stable xylanase derived from Bacillus pumilus HBP8, was extracellularly produced in E. coli cells through N-terminal-fused signal peptides. We found that the matured XynHB itself could be auto-secreted out of E. coli BL21(DE3) cells at a very low level, and two Sec-pathway signal peptides, PelB and OmpA, and one dual Sec-Tat-pathway signal peptide, FhuD, could effectively prompt its extracellular production up to 12-fold. Our results showed that PelB signal peptide led to the highest extracellular production of XynHB for approximately 54.1 μg/mL, and FhuD-fused XynHB possessed the highest specific activity of 1746.0 U/mg at 70 °C. Meanwhile, our studies also indicated that PelB- and FhuD-fused XynHB might disrupt E. coli cells' periplasm during their secretion process, thus causing cell lysis to facilitate their extracellular production. Moreover, further characterization revealed that the extracellular production of XynHB was not affected by the outer membrane permeability of E. coli cells. Our studies provided an advantageous strategy for the extracellular production of xylanase in E. coli, which may also be used for E. coli autolysis in the future.

Increased production of periplasmic proteins in Escherichia coli by directed evolution of the translation initiation region

Background

Recombinant proteins are often engineered with an N-terminal signal peptide, which facilitates their secretion to the oxidising environment of the periplasm (gram-negative bacteria) or the culture supernatant (gram-positive bacteria). A commonly encountered problem is that the signal peptide influences the synthesis and secretion of the recombinant protein in an unpredictable manner. A molecular understanding of this phenomenon is highly sought after, as it could lead to improved methods for producing recombinant proteins in bacterial cell factories.

Results

Herein we demonstrate that signal peptides contribute to an unpredictable translation initiation region. A directed evolution approach that selects a new translation initiation region, whilst leaving the amino acid sequence of the signal peptide unchanged, can increase production levels of secreted recombinant proteins. The approach can increase production of single chain antibody fragments, hormones and other recombinant proteins in the periplasm of E. coli.

Conclusions

The study demonstrates that signal peptide performance is coupled to the efficiency of the translation initiation region.

Efficient keratinase expression via promoter engineering strategies for degradation of feather wastes

Keratinases are promising alternatives over ordinary proteases in several industrial applications due to their unique properties compared with their counterparts in the protease categories. However, their large-scale industrial application is limited by the low expression and poor fermentation efficiency of keratinase. Here, we demonstrate that the expression level of keratinase can be improved by constructing a more efficient enzyme expression system hereby enables the highest production titer as regarding recombinant keratinase production to date. Specially, ten promoters were evaluated and the aprE promoter exhibits a significant promotion of keratinase (kerBv) titer from 165 U/mL to 2605 U/mL in Bacillus subtilis. The batch fermentation mode resulted in a maximum keratinase activity of 7176 U/mL at 36 h in a 5-L fermenter. Furthermore, the extracellular keratinase activity attained up to 16,860 U/mL via fed-batch fermentation within 30 h. The combination of keratinase with l-cysteine brings about 66.4 % degree of degradation of feather. Our work provides a new insight into the development of efficient keratinase fermentation processes with B. subtilis cell factory.

Enhanced periplasmic expression of human activin A in Escherichia coli using a modified signal peptide

Activin A is a member of the transforming growth factor-beta (TGF-β) protein superfamily, which acts as a hormone in regulating cell proliferation and differentiation. Structurally, activin is a dimer of two subunits linked by a disulfide bond. Since the correct folding of this protein is essential for its function, we aimed to use a modified signal peptide to target the expressed recombinant protein to the periplasm of Escherichia coli as an effective strategy to produce correctly-folded activin A. Therefore, the coding sequence of native Iranian Bacillus licheniformis α-amylase signal peptide was modified and its efficiency was checked by SignalP bioinformatics tool. Then its final sequence was cloned upstream of the activin A mature cDNA. Protein expression was done using 1 mM of isopropyl thio-β-D-galactoside (IPTG) and a post-induction time of 8 hr. Additionally, following purification of recombinant activin A, circular dichroism spectroscopy was used to determine the accuracy of secondary structure of the protein. Importantly, differentiation of K562 cells to the red blood cell was confirmed by measuring the amount of Fe⁺² ions after treatment with recombinant activin A. The results indicated that the produced recombinant activin A had the same secondary structure as the commercial human activin A and was fully functional.

Production and Purification of Recombinant Toxins

Recombinant expression of toxins enables us to produce adequate quantities of these proteins which can be used to perform experiments at molecular, cellular, and behavioral levels. Furthermore, toxins can be edited by using simple molecular biology methods when producing them recombinantly. Thus, in many cases establishing a protocol for the recombinant expression of a toxin of interest is crucial in exploring the structure and function of the toxin and its effectors. To date, Escherichia coli (E. coli) represents the most widely used heterologous expression system in which recombinant proteins are usually accumulated in the bacterium cytoplasm. However, as many animal toxins contain disulfide bonds they tend to be misfolded and aggregate when found in the reducing E. coli cytoplasm. In contrast, conditions in the bacterium periplasm allow disulfide bond formation and correct folding of such toxins. Here, we describe a protocol for the production and purification of bioactive recombinant disulfide-rich toxins via periplasmic expression.

Extracellular expression of Aerococcus viridans pyruvate oxidase in recombinant Escherichia coli through SecB co-expression

Pyruvate oxidase (POD) is an important enzyme used for clinical applications and biochemical analyses, and recombinant Escherichia coli strains expressing Aerococcus viridans POD have been frequently employed for obtaining high POD yield. Although significant progress has been achieved in increasing recombinant POD production, intracellular POD expression and weak stability of POD make POD purification difficult. In this study, extracellular POD expression was achieved by co-expression of chaperone SecB under three promoters (T7, lac, bla). The weakest promoter, bla, when compared with T7 and lac promoters, provided the optimum extracellular POD activity among these three promoters. After optimization of cultivation conditions, such as IPTG concentration, pH, and temperature, the extracellular POD yield increased to 795.7 U L-1. Furthermore, by using glycine to disrupt recombinant E. coli cell wall and Cu2+ ions as POD stabilizer, the final extracellular POD yield reached 2926.3 U L-1. The expression intensity of chaperone had significant influence on heterologous protein secretion, and the high yield of extracellular POD implies potential widespread POD production and application.

Enhancing Recombinant Protein Yields in the E. coli Periplasm by Combining Signal Peptide and Production Rate Screening

Proteins that contain disulfide bonds mainly mature in the oxidative environment of the eukaryotic endoplasmic reticulum or the periplasm of Gram-negative bacteria. In E. coli, disulfide bond containing recombinant proteins are often targeted to the periplasm by an N-terminal signal peptide that is removed once it passes through the Sec-translocon in the cytoplasmic membrane. Despite their conserved targeting function, signal peptides can impact recombinant protein production yields in the periplasm, as can the production rate. Here, we present a combined screen involving different signal peptides and varying production rates that enabled the identification of more optimal conditions for periplasmic production of recombinant proteins with disulfide bonds. The data was generated from two targets, a single chain antibody fragment (BL1) and human growth hormone (hGH), with four different signal peptides and a titratable rhamnose promoter-based system that enables the tuning of protein production rates. Across the screen conditions, the yields for both targets significantly varied, and the optimal signal peptide and rhamnose concentration differed for each protein. Under the optimal conditions, the periplasmic BL1 and hGH were properly folded and active. Our study underpins the importance of combinatorial screening approaches for addressing the requirements associated with the production of a recombinant protein in the periplasm.

Factors Influencing Recombinant Protein Secretion Efficiency in Gram-Positive Bacteria: Signal Peptide and Beyond

Signal peptides are short peptides directing newly synthesized proteins toward the secretory pathway. These N-terminal signal sequences are ubiquitous to all prokaryotes and eukaryotes. Signal peptides play a significant role in recombinant protein production. Previous studies have demonstrated that the secretion amount of a given target protein varies significantly depending on the signal peptide that is fused to the protein. Signal peptide selection and signal peptide modification are the two main methods for the optimization of a recombinant protein secretion. However, the highly efficient signal peptide for a target protein with a specific bacterial expression host is not predictable so far. In this article, we collect several signal peptides that have previously performed well for recombinant protein secretion in gram-positive bacteria. We also discuss several factors influencing recombinant protein secretion efficiency in gram-positive bacteria. Signal peptides with a higher charge/length ratio in n-region, more consensus residues at the-3 and-1positions in c-region and a much higher proportion of coils are more likely to perform well in the secretion of recombinant proteins. These summaries can be utilized to the selection and directed modification of signal peptides for a given recombinant protein.

Optimizing Periplasmic Expression in Escherichia coli for the Production of Recombinant Proteins Tagged with the Small Metal-Binding Protein SmbP

We have previously shown that the small metal-binding protein (SmbP) extracted from the gram-negative bacterium Nitrosomonas europaea can be employed as a fusion protein for the expression and purification of recombinant proteins in Escherichia coli. With the goal of increasing the amounts of SmbP-tagged proteins produced in the E. coli periplasm, we replaced the native SmbP signal peptide with three different signal sequences: two were from the proteins CusF and PelB, for transport via the Sec pathway, and one was the signal peptide from TorA, for transport via the Tat pathway. Expression of SmbP-tagged Red Fluorescent Protein (RFP) using these three alternative signal peptides individually showed a considerable increase in protein levels in the periplasm of E. coli as compared to its level using the SmbP signal sequence. Therefore, for routine periplasmic expression and purification of recombinant proteins in E. coli, we highly recommend the use of the fusion proteins PelB-SmbP or CusF-SmbP, since these signal sequences increase periplasmic production considerably as compared to the wild-type. Our work, finally, demonstrates that periplasmic expression for SmbP-tagged proteins is not limited to the Sec pathway, in that the TorA-SmbP construct can export reasonable quantities of folded proteins to the periplasm. Although the Sec route has been the most widely used, sometimes, depending on the nature of the protein of interest, for example, if it contains cofactors, it is more appropriate to consider using the Tat route over the Sec. SmbP therefore can be recommended in terms of its particular versatility when combined with signal peptides for the two different routes.

Implementation of a novel self-induced promoter for the expression of pharmaceutical peptides in Escherichia coli: YY(3-36) peptide

Background

Increasing the expression rate of recombinant mammalian hormones in Escherichia coli by combining efficient promoters and signal sequences is a never ending process. A self-induced promoter will have some beneficial gains compared to the classical T7 promoter or its variants with isopropyl β-D-1-thiogalactopyranoside (IPTG) as the inducer. Obesity is the prime suspect in widespread frequency of diabetes type II and cardiovascular diseases worldwide. YY (tyrosine-tyrosine) peptide is a local acting hormone, controlling appetite. Excitingly, it was has been shown that a truncated version of the YY peptide, YY(3-36) peptide, has potential as a worthy biopharmaceutical agent in the fight against obesity.

Materials and methods

To develop an economical expression system for the large scale production of the peptide in Gram-negative bacteria, we introduced a promoter sequence upstream of a chimeric gene for the extracellular expression of this peptide with the assistance of a signal sequence of asparaginase II from E. coli. This system has the advantage of producing a complete sequence of a truncated YY peptide, YY(3-36), without any extra tags that would require further removal with the assistance of expensive specific proteases and reduced the downstream steps, significantly.

Results

Recombinant production of YY(3-36) peptide under a self-induced promoter proves the efficacy of the asparaginase II signal sequence as a communicator of foreign peptides and proteins into the extracellular space of E. coli.

Conclusions

The application of fusion protein expression of biopharmaceuticals, especially mammalian hormones, in prokaryotic systems with the help of native signal sequences makes some common tags with expensive proteases for the removal of the attached protein Tag redundant.