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Production of Pentameric Cholera Toxin B Subunit in Escherichia coli.

ABSTRACT: Cholera toxin B subunit (CTB) has been extensively studied as an immunogen, adjuvant, and inducer of oral tolerance in many investigations. Production of CTB has been carried out in the bacterial, plant, insect and yeast expression systems. In this study the expression of the CTB containing a 6XHis-tagged was performed by Escherichia coli (E.coli) M15. The yield of purified pentameric recombinant CTB was about 1 mg/l. Western blot analysis demonstrated that the recombinant CTB was antigenically active. In addition, GM1-ganglioside ELISA showed that recombinant CTB binds to GM1-gangelioside receptor, confirming disulfide bond formation and proper folding of the recombinant protein in E.coli. Overall, in regard to the vast applications of CTB in medicine, this bacterial expression system will be a fast, cost-effective and simple system for production of pentameric CTB and CTB conjugated proteins.

SUBMITTER: Dakterzada F

PROVIDER: S-EPMC3558211 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Production of Pentameric Cholera Toxin B Subunit in Escherichia coli.

Dakterzada Farida F Mobarez Ashraf Mohabati AM Roudkenar Mehryar Habibi MH Forouzandeh Mehdi M

Avicenna journal of medical biotechnology 20120401 2

Cholera toxin B subunit (CTB) has been extensively studied as an immunogen, adjuvant, and inducer of oral tolerance in many investigations. Production of CTB has been carried out in the bacterial, plant, insect and yeast expression systems. In this study the expression of the CTB containing a 6XHis-tagged was performed by Escherichia coli (E.coli) M15. The yield of purified pentameric recombinant CTB was about 1 mg/l. Western blot analysis demonstrated that the recombinant CTB was antigenically ...[more]

PMID: 23408749

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Project description:Non-toxic derivatives of the cholera toxin are extensively used in neuroscience, as neuronal tracers to reveal the location of cells in the central nervous system. They are, also, being developed as vaccine components and drug-delivery vehicles. Production of cholera-toxin derivatives is often non-reproducible; the quality and quantity require extensive fine-tuning to produce them in lab-scale settings. In our studies, we seek a resolution to this problem, by expanding the molecular toolbox of the Escherichia coli expression system with suitable production, purification, and offline analytics, to critically assess the quality of a probe or drug delivery, based on a non-toxic derivative of the cholera toxin. We present a re-engineered Cholera Toxin Complex (rCTC), wherein its toxic A1 domain was replaced with Maltose Binding Protein (MBP), as a model for an rCTC-based targeted-delivery vehicle. Here, we were able to improve the rCTC production by 11-fold (168 mg/L vs. 15 mg/L), in comparison to a host/vector combination that has been previously used (BL21(DE3) pTRBAB5-G1S). This 11-fold increase in the rCTC production capability was achieved by (1) substantial vector backbone modifications, (2) using Escherichia coli strains capable of growth-decoupling (V strains), (3) implementing a well-tuned fed-batch production protocol at a 1 L scale, and (4) testing the stability of the purified product. By an in-depth characterization of the production process, we revealed that secretion of rCTC across the E. coli Outer Membrane (OM) is processed by the Type II secretion-system general secretory pathway (gsp-operon) and that cholera toxin B-pentamerization is, likely, the rate-limiting step in complex formation. Upon successful manufacturing, we have validated the biological activity of rCTC, by measuring its binding affinity to its carbohydrate receptor GM1 oligosaccharide (Kd = 40 nM), or binding to Jurkat cells (93 pM) and delivering the cargo (MBP) in a retrograde fashion to the cell.

Project description:IntroductionCholera toxin B subunit (CTB) is a component of an internationally licensed oral cholera vaccine. The protein induces neutralizing antibodies against the holotoxin, the virulence factor responsible for severe diarrhea. A field clinical trial has suggested that the addition of CTB to killed whole-cell bacteria provides superior short-term protection to whole-cell-only vaccines; however, challenges in CTB biomanufacturing (i.e., cost and scale) hamper its implementation to mass vaccination in developing countries. To provide a potential solution to this issue, we developed a rapid, robust, and scalable CTB production system in plants.Methodology/principal findingsIn a preliminary study of expressing original CTB in transgenic Nicotiana benthamiana, the protein was N-glycosylated with plant-specific glycans. Thus, an aglycosylated CTB variant (pCTB) was created and overexpressed via a plant virus vector. Upon additional transgene engineering for retention in the endoplasmic reticulum and optimization of a secretory signal, the yield of pCTB was dramatically improved, reaching >1 g per kg of fresh leaf material. The protein was efficiently purified by simple two-step chromatography. The GM1-ganglioside binding capacity and conformational stability of pCTB were virtually identical to the bacteria-derived original B subunit, as demonstrated in competitive enzyme-linked immunosorbent assay, surface plasmon resonance, and fluorescence-based thermal shift assay. Mammalian cell surface-binding was corroborated by immunofluorescence and flow cytometry. pCTB exhibited strong oral immunogenicity in mice, inducing significant levels of CTB-specific intestinal antibodies that persisted over 6 months. Moreover, these antibodies effectively neutralized the cholera holotoxin in vitro.Conclusions/significanceTaken together, these results demonstrated that pCTB has robust producibility in Nicotiana plants and retains most, if not all, of major biological activities of the original protein. This rapid and easily scalable system may enable the implementation of pCTB to mass vaccination against outbreaks, thereby providing better protection of high-risk populations in developing countries.

Dataset Information

Production of Pentameric Cholera Toxin B Subunit in Escherichia coli.

Publications

Production of Pentameric Cholera Toxin B Subunit in Escherichia coli.

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