Recombinant production of influenza hemagglutinin and HIV-1 GP120 antigenic peptides using a cleavable self-aggregating tag

Cleavable Self-Aggregating Tags (cSAT) for Therapeutic Peptide Expression and Purification

Efficient protein and peptide expression and purification technologies are highly needed in biotechnology, especially in light of the increasing number of proteins and peptides that are being exploited for therapeutic use, which are inherently difficult to produce via biological means. In this chapter, we describe a facile, reliable, and cost-effective peptide production and purification strategy based on short self-assembling peptides (e.g., L₆KD (LLLLLLKD)) and a C-terminal cleavage intein (e.g., Mtu ΔI-CM). This cleavable self-aggregating tag (cSAT) scheme depends on the in vivo formation of aggregates of the fusion protein containing the target peptide, which is induced during the expression by the presence of the self-assembling peptide in the construct. After a simple separation of the aggregates by centrifugation, the purified target peptide with authentic N-terminus is released in solution by pH-induced intein self-cleavage. As an example, a yield of about 4.4 μg/mg wet cell pellet was obtained when the cSAT scheme was used for the expression and purification of the therapeutic peptide GLP-1. This strategy provides a viable approach for preparing peptides with authentic N-termini, especially those in the range of 30 ~ 100 amino acids in size that are typically unstable or susceptible to degradation in Escherichia coli.

Recombinant Production of Bovine Enteropeptidase Light Chain in SHuffle® T7 Express and Optimization of Induction Parameters

Enteropeptidase is a duodenum serine protease that triggers the activation of pancreatic enzymes by remarkably specific cleavages after lysine residues of peptidyl substrate (Asp)₄-Lys. This high specific cleavage makes the enzyme a widely used biotechnological tool in laboratory researches and industrial scale. Previous studies both in small and large scales were showed low expression and miss-folding of the expressed protein. In this study, the DNA sequence encoding the light chain (catalytic subunit) of bovine enteropeptidase (EP_L) was subcloned into plasmid pET-32b, downstream to the DNA encoding the fusion partner thioredoxin immediately after the EP_L cleavage site. SHuffle® T7 Express was selected as an expression host due to the ability to promote proper folding and correction of the mis-oxidized bonds. Expression and purification of protein was performed, and the result of biological activity confirmed that the active EP_L was obtained. Optimization of protein expression conditions was accomplished by response surface methodology for significant factors including induction temperature, duration of induction, inducer concentration and OD₆₀₀ of induction. The best conditions were achieved in 1.05 mM IPTG at OD₆₀₀ of 0.6 for seven h incubation at 26.5 °C, and a high level of protein expression was obtained in the optimized condition.

Catalytically-active inclusion bodies for biotechnology-general concepts, optimization, and application

Bacterial inclusion bodies (IBs) have long been considered as inactive, unfolded waste material produced by heterologous overexpression of recombinant genes. In industrial applications, they are occasionally used as an alternative in cases where a protein cannot be expressed in soluble form and in high enough amounts. Then, however, refolding approaches are needed to transform inactive IBs into active soluble protein. While anecdotal reports about IBs themselves showing catalytic functionality/activity (CatIB) are found throughout literature, only recently, the use of protein engineering methods has facilitated the on-demand production of CatIBs. CatIB formation is induced usually by fusing short peptide tags or aggregation-inducing protein domains to a target protein. The resulting proteinaceous particles formed by heterologous expression of the respective genes can be regarded as a biologically produced bionanomaterial or, if enzymes are used as target protein, carrier-free enzyme immobilizates. In the present contribution, we review general concepts important for CatIB production, processing, and application. KEY POINTS: • Catalytically active inclusion bodies (CatIBs) are promising bionanomaterials. • Potential applications in biocatalysis, synthetic chemistry, and biotechnology. • CatIB formation represents a generic approach for enzyme immobilization. • CatIB formation efficiency depends on construct design and expression conditions.

Human respiratory syncytial virus F protein expressed in Pichia pastoris or Escherichia coli induces protective immunity without inducing enhanced respiratory disease in mice

Human respiratory syncytial virus (hRSV) is the primary cause of severe respiratory tract disease in children and infants as well as in elderly and immunocompromised adults. The fusion protein (F) of hRSV is the major antigen eliciting a neutralizing antibody response and protective immunity in the host, especially those recognizing the prefusion F protein (pre-F). In this study, we made genetic constructs for expression of a recombinant prefusion F protein in Pichia pastoris GS115, called RGF. Using Escherichia coli BL21, we expressed the pre-F and postfusion F protein (Post-F), called RBF and Post-RBF, respectively. RGF and RBF showed high affinity for 5C4, a highly potent monoclonal antibody specific for pre-F. We studied the immunogenicity of RGF and RBF in mice. Compared to mice immunized with formalin-inactivated RSV (FI-RSV), mice immunized with RGF or RBF exhibited superior protective immunity, which was confirmed by serum neutralizing activity and viral clearance after challenge. As judged from the IgG1/IgG2a ratios and numbers of IFN-γ- and IL-4-secreting cells, RGF or RBF with alum adjuvant induced a balanced Th1-biased immune response and produced no signs of enhanced respiratory disease (ERD) upon hRSV challenge. In addition, the immunogenicity and protective efficacy of RGF were superior to those of RBF in mice. Therefore, RGF represents a potential vaccine candidate for the prevention of human infection with hRSV.

Emerging biomaterials for downstream manufacturing of therapeutic proteins

Downstream processing is considered one of the most challenging phases of industrial manufacturing of therapeutic proteins, accounting for a large portion of the total production costs. The growing demand for therapeutic proteins in the biopharmaceutical market in addition to a significant rise in upstream titers have placed an increasing burden on the downstream purification process, which is often limited by high cost and insufficient capacities. To achieve efficient production and reduced costs, a variety of biomaterials have been exploited to improve the current techniques and also to develop superior alternatives. In this work, we discuss the significance of utilizing traditional biomaterials in downstream processing and review the recent progress in the development of new biomaterials for use in protein separation and purification. Several representative methods will be highlighted and discussed in detail, including affinity chromatography, non-affinity chromatography, membrane separations, magnetic separations, and precipitation/phase separations. STATEMENT OF SIGNIFICANCE: Nowadays, downstream processing of therapeutic proteins is facing great challenges created by the rapid increase of the market size and upstream titers, starving for significant improvements or innovations in current downstream unit operations. Biomaterials have been widely used in downstream manufacturing of proteins and efforts have been continuously devoted to developing more advanced biomaterials for the implementation of more efficient and economical purification methods. This review covers recent advances in the development and application of biomaterials specifically exploited for various chromatographic and non-chromatographic techniques, highlighting several promising alternative strategies.

A novel protein purification strategy mediated by the combination of CipA and Ssp DnaB intein

Protein purification is an indispensable step in diverse fields of biological research or production process. Conventional purification methods including the affinity purification or the usage of self-aggregating tags suffered from many drawbacks such as the complicated steps, high cost and low efficiency. Moreover, the fusion tag usually had negative effects on the activity of the target protein. To address the above issues, here we propose a novel protein purification method which needs simple operation steps, and this method is mediated by the combination of CipA protein and a mini-intein (Synechocystis sp. PCC6803 DnaB, Ssp DnaB), depending on the assembly function of CipA and the self-cleavage function of Ssp DnaB. To realize the purification, CipA-DnaB-eGFP protein was expressed and assembled into protein crystalline inclusions (PCIs) in E. coli. Then, only cell lysis, cleavage and centrifugation steps were required to purify eGFP. Purified eGFP was in the supernatant with a purity of over 90%. The cleavage efficiency and the yield of eGFP reached 51.96% and 13.99 ± 0.88 mg/L fermentation broth, respectively. Furthermore, to broaden the application of this approach, three other proteins which were maltose binding protein (MBP), ketoisovalerate decarboxylase (Kivd) and alcohol dehydrogenase (AdhP) were purified with high cleavage efficiency. The purified Kivd and AdhP remained high specific activities. This work demonstrated an effective and convenient protein purification method.

Design, expression, and characterization of a novel cecropin A-derived peptide with high antibacterial activity

In recent years, antimicrobial peptides have received increased interest and are potential substitutes for antibiotics. However, natural antimicrobial peptides are always toxic to mammalian cells and usually exhibit weak antibacterial activity, which restrict their wide application. In this study, a novel antibacterial peptide named PEW300 was designed with three mutations to the parental peptide cecropin A. As predicted by bioinformatic programs, the positive charge of PEW300 increased from + 6 to + 9 compared with cecropin A, and the grand average of hydropathicity increased from - 0.084 to - 0.008. Expression of PEW300 resulted in serious inhibition of Escherichia coli BL21(DE3) cells, indicating designed PEW300 may have stronger antibacterial activity. A simple, fast, and low-cost approach without tedious protein purification steps was selected for the efficient production of PEW300 by fusion with ELK16 and about 7.38 μg/mg wet cell weight PEW300 was eventually obtained. Purified PEW300 exhibited strong antibacterial activity against various Gram-positive and Gram-negative bacteria which was enhanced four- to sevenfold compared with the parental peptide cecropin A. Besides, PEW300 had no hemolytic activity toward mammalian cells even at high concentration (224 ng/μl). PEW300 showed good stability in neutral and alkaline solutions. Moreover, PEW300 was thermally stable even at up to 100 °C and resistant to proteinase K, pepsin, snailase, and trypsin. The incubation with human serum had no effect on the antibacterial activity of PEW300. All these results demonstrated that PEW300 designed in this work may have good potential as a candidate pharmaceutical agent.

Rapid and efficient production of cecropin A antibacterial peptide in Escherichia coli by fusion with a self-aggregating protein

BACKGROUND

Cecropin A (CeA), a natural cationic antimicrobial peptide, exerts potent antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, making it an attractive candidate substitute for antimicrobials. However, the low production rate and cumbersome, expensive processes required for both its recombinant and chemical synthesis have seriously hindered the exploitation and application of CeA. Here, we utilized a short β-structured self-aggregating protein, ELK16, as a fusion partner of CeA, which allowed the efficient production of high-purity CeA antibacterial peptide with a simple inexpensive process.

RESULTS

In this study, three different approaches to the production of CeA peptide were investigated: an affinity tag (His-tag)-fused protein expression system (AT-HIS system), a cell-free protein expression system (CF system), and a self-assembling peptide (ELK16)-fused protein expression system (SA-ELK16 system). In the AT-HIS and CF systems, the CeA peptide was obtained with purities of 92.1% and 90.4%, respectively, using one or more affinity-chromatographic purification steps. The procedures were tedious and costly, with CeA yields of only 0.41 and 0.93 μg/mg wet cell weight, respectively. Surprisingly, in the SA-ELK16 system, about 6.2 μg/mg wet cell weight of high-purity (approximately 99.8%) CeA peptide was obtained with a simple low-cost process including steps such as centrifugation and acetic acid treatment. An antimicrobial test showed that the high-purity CeA produced in this study had the same antimicrobial activity as synthetic CeA peptide.

CONCLUSIONS

In this study, we designed a suitable expression system (SA-ELK16 system) for the production of the antibacterial peptide CeA and compared it with two other protein expression systems. A high yield of high-purity CeA peptide was obtained with the SA-ELK16 system, which greatly reduced the cost and time required for downstream processing. This system may provide a platform for the laboratory scale production of the CeA antibacterial peptide.

New trends in aggregating tags for therapeutic protein purification

The rapid growth of the therapeutic protein market calls for more efficient purification methods. Various aggregating tags have recently emerged as simple, fast, cost-effective and column-free technologies for protein (and peptide) purification. In general, these column-free protein purification technologies involve the use of aggregating tags that induce the target protein into insoluble aggregates. These aggregates can be easily separated from soluble impurities and the target protein or peptide is then liberated by a cleavage process. This review summarizes the current state-of-the-art in using aggregating tags for protein purification. The methods are here categorized as follows: (1) tags that allow soluble expression of target protein in vivo and induce aggregation in vitro; (2) tags that induce soluble expression and self-assembling of target protein on insoluble biological polyester beads in vivo; (3) tags that induce formation of inactive aggregates in vivo; (4) tags that induce formation of active aggregates in vivo.

A novel secretion and online-cleavage strategy for production of cecropin A in Escherichia coli

Antimicrobial peptides, promising antibiotic candidates, are attracting increasing research attention. Current methods for production of antimicrobial peptides are chemical synthesis, intracellular fusion expression, or direct separation and purification from natural sources. However, all these methods are costly, operation-complicated and low efficiency. Here, we report a new strategy for extracellular secretion and online-cleavage of antimicrobial peptides on the surface of Escherichia coli, which is cost-effective, simple and does not require complex procedures like cell disruption and protein purification. Analysis by transmission electron microscopy and semi-denaturing detergent agarose gel electrophoresis indicated that fusion proteins contain cecropin A peptides can successfully be secreted and form extracellular amyloid aggregates at the surface of Escherichia coli on the basis of E. coli curli secretion system and amyloid characteristics of sup35NM. These amyloid aggregates can be easily collected by simple centrifugation and high-purity cecropin A peptide with the same antimicrobial activity as commercial peptide by chemical synthesis was released by efficient self-cleavage of Mxe GyrA intein. Here, we established a novel expression strategy for the production of antimicrobial peptides, which dramatically reduces the cost and simplifies purification procedures and gives new insights into producing antimicrobial and other commercially-viable peptides.