Highly efficient expression of Escherichia coli heat-labile enterotoxin B subunit in plants using potato virus X-based vector

Expression of Escherichia coli Heat-Labile Enterotoxin B Subunit in Centella (Centella asiatica (L.) Urban) via Biolistic Transformation

BACKGROUND

Heat-Labile enterotoxin B subunit (LTB) produced by Escherichia coli, a non-toxic protein subunit with potential biological properties, is a powerful mucosal and parenteral adjuvant which can induce a strong immune response against co-administered antigens.

OBJECTIVE

In the present study, LTB protein, encoded by the optimized ltb (also known synthetic ltb, s-ltb) gene in centella plant (Centella asiatica) for use as an antigen, has been discussed.

METHODS

The s-ltb gene was cloned into a plant expression vector, pMYO51, adjacent to the CaMV 35S promoter and was then introduced into centella plant by biolistic transformation. PCR amplification was conducted to determine the presence of s-ltb gene in the transgenic centella plant. The expression of s-ltb gene was analyzed by immunoblotting and quantified by ELISA. In vitro activity of LTB protein was determined by GM1-ELISA.

RESULTS

PCR amplification has found seven transgenic centella individuals. However, only five of them produced LTB protein. ELISA analysis showed that the highest amount of LTB protein detected in transgenic centella leaves was about 0.8% of the total soluble protein. GM1-ELISA assay indicated that plant LTB protein bound specifically to GM1-ganglioside, suggesting that the LTB subunits formed active pentamers.

CONCLUSION

The s-ltb gene that was successfully transformed into centella plants by the biolistic method has produced a relatively high amount of plant LTB protein in the pentameric quaternary structure that has GM1-ganglioside binding affinity, a receptor on the intestinal epithelial membrane.

LTB-Syn: a recombinant immunogen for the development of plant-made vaccines against synucleinopathies

A recombinant antigen targeting α-synuclein was produced in the plant cell rendering an immunogenic protein capable to induce humoral responses in mice upon oral administration. Synucleinopathies are neurodegenerative diseases characterized by the abnormal accumulation of α-synuclein (α-Syn, a 140 amino acid protein that normally plays various neurophysiologic roles) aggregates. Parkinson's disease (PD) is the synucleinopathy with the highest epidemiologic impact and although its etiology remains unknown, α-Syn aggregation during disease progression pointed out α-Syn as target in the development of immunotherapies. Herein a chimeric protein, comprising the B subunit of the enterotoxin from enterotoxigenic Escherichia coli and α-Syn epitopes, was expressed in the plant cell having the potential to induce humoral responses following oral immunization. This approach will serve as the basis for the development of oral plant-based vaccines against PD with several potential advantages such as low cost, easy scale-up during production, and easy administration.

AB toxins: a paradigm switch from deadly to desirable

To ensure their survival, a number of bacterial and plant species have evolved a common strategy to capture energy from other biological systems. Being imperfect pathogens, organisms synthesizing multi-subunit AB toxins are responsible for the mortality of millions of people and animals annually. Vaccination against these organisms and their toxins has proved rather ineffective in providing long-term protection from disease. In response to the debilitating effects of AB toxins on epithelial cells of the digestive mucosa, mechanisms underlying toxin immunomodulation of immune responses have become the focus of increasing experimentation. The results of these studies reveal that AB toxins may have a beneficial application as adjuvants for the enhancement of immune protection against infection and autoimmunity. Here, we examine similarities and differences in the structure and function of bacterial and plant AB toxins that underlie their toxicity and their exceptional properties as immunomodulators for stimulating immune responses against infectious disease and for immune suppression of organ-specific autoimmunity.