Expression and purification of hepatitis B surface antigen S from Escherichia coli; a new simple method

Recent Progress on Vaccines Produced in Transgenic Plants

The development of vaccines from plants has been going on for over two decades now. Vaccine production in plants requires time and a lot of effort. Despite global efforts in plant-made vaccine development, there are still challenges that hinder the realization of the final objective of manufacturing approved and safe products. Despite delays in the commercialization of plant-made vaccines, there are some human vaccines that are in clinical trials. The novel coronavirus (SARS-CoV-2) and its resultant disease, coronavirus disease 2019 (COVID-19), have reminded the global scientific community of the importance of vaccines. Plant-made vaccines could not be more important in tackling such unexpected pandemics as COVID-19. In this review, we explore current progress in the development of vaccines manufactured in transgenic plants for different human diseases over the past 5 years. However, we first explore the different host species and plant expression systems during recombinant protein production, including their shortcomings and benefits. Lastly, we address the optimization of existing plant-dependent vaccine production protocols that are aimed at improving the recovery and purification of these recombinant proteins.

A Novel Surface-Exposed Polypeptide Is Successfully Employed as a Target for Developing a Prototype One-Step Immunochromatographic Strip for Specific and Sensitive Direct Detection of Staphylococcus aureus Causing Neonatal Sepsis

Neonatal sepsis is a life-threatening condition and Staphylococcus aureus is one of its major causes. However, to date, no rapid and sensitive diagnostic tool has been developed for its direct detection. Bioinformatics analyses identified a surface-exposed 112-amino acid polypeptide of the cell wall protein NWMN_1649, a surface protein involved in cell aggregation and biofilm formation, as being a species-specific and highly conserved moiety. The polypeptide was cloned, purified, and used to immunize mice to raise specific immunoglobulins. The purified antibodies were conjugated to gold nano-particles and used to assemble an immunochromatographic strip (ICS). The developed prototype ICS detected as low as 5 µg purified polypeptide and 102 CFU/mL S. aureus within 15 min. The strip showed superior ability to directly detect S. aureus in neonatal sepsis blood specimens without prior sample processing. Moreover, it showed no cross-reaction in specimens infected with two other major causes of neonatal sepsis; coagulase-negative staphylococci and Klebsiella pneumoniae. The selected NWMN_1649-derived polypeptide demonstrates success as a promising biomolecule upon which a prototype ICS has been developed. This ICS provides a rapid, direct, sensitive, and specific option for the detection of S. aureus causing neonatal sepsis. Such a tool is urgently needed especially in resources-limited countries.

Effects of mRNA secondary structure on the expression of HEV ORF2 proteins in Escherichia coli

Background

Viral protein expression in Escherichia coli (E. coli) is a powerful tool for structural/functional studies as well as for vaccine and diagnostics development. However, numerous factors such as codon bias, mRNA secondary structure and nucleotides distribution, have been indentified to hamper this heterologous expression.

Results

In this study, we combined computational and biochemical methods to analyze the influence of these factors on the expression of different segments of hepatitis E virus (HEV) ORF 2 protein and hepatitis B virus surface antigen (HBsAg). Three out of five HEV antigens were expressed while all three HBsAg fragments were not. The computational analysis revealed a significant difference in nucleotide distribution between expressed and non-expressed genes; and all these non-expressing constructs shared similar stable 5′-end mRNA secondary structures that affected the accessibility of both Shine-Dalgarno (SD) sequence and start codon AUG. By modifying the 5′-end of HEV and HBV non-expressed genes, there was a significant increase in the total free energy of the mRNA secondary structures that permitted the exposure of the SD sequence and the start codon, which in turn, led to the successful expression of these genes in E. coli.

Conclusions

This study demonstrates that the mRNA secondary structure near the start codon is the key limiting factor for an efficient expression of HEV ORF2 proteins in E. coli. It describes also a simple and effective strategy for the production of viral proteins of different lengths for immunogenicity/antigenicity comparative studies during vaccine and diagnostics development.

Electronic supplementary material

The online version of this article (10.1186/s12934-017-0812-8) contains supplementary material, which is available to authorized users.

Synthesis and assembly of Hepatitis B virus envelope protein-derived particles in Escherichia coli

Hepatitis B virus (HBV) envelope particles have been synthesized in eukaryotic cells (e.g., mammalian cells, insect cells, and yeast cells) as an HB vaccine immunogen and drug delivery system (DDS) nanocarrier. Many researchers had made attempts to synthesize the particles in Escherichia coli for minimize the cost and time for producing HBV envelope particles, but the protein was too deleterious to be synthesized in E. coli. In this study, we generated deletion mutants of HBV envelope L protein (389 amino acid residues (aa)) containing three transmembrane domains (TM1, TM2, TM3). The ΔNC mutant spanning from TM2 to N-terminal half of TM3 (from 237 aa to 335 aa) was found as a shortest form showing spontaneous particle formation. After the N-terminal end of ΔNC mutant was optimized by the N-end rule for E. coli expression, the modified ΔNC mutant (mΔNC) was efficiently expressed as particles in E. coli. The molecular mass of mΔNC particle was approx. 670 kDa, and the diameter was 28.5 ± 6.2 nm (mean ± SD, N = 61). The particle could react with anti-HBV envelope S protein antibody, indicating the particles exhibited S antigenic domain outside as well as HBV envelope particles. Taken together, the E. coli-derived mΔNC particles could be used as a substitute of eukaryotic cell-derived HBV envelope particles for versatile applications.

Exposition of hepatitis B surface antigen (HBsAg) on the surface of HEK293T cell and evaluation of its expression

Hepatitis B virus (HBV) is considered as a global health concern and hepatitis B surface antigen (HBsAg) is the most immunogenic protein of HBV. The purpose of this study was to evaluate the expression of HBsAg on the cell surface of human embryonic kidney cell line (HEK293T). After transformation of expression vector pcDNA/HBsAg to E.coli TOP10F’, plasmid was extracted and digested with BglII. Afterwards, the linearized vector was transfected to cells and treated with hygromycin B for 5 weeks to expand the resulted clonies. The permanent expression of HBsAg followed by flow cytometry uptill now about one year. Genomic DNA was extracted from transfected cells and the existence of HBsAg gene was assessed by PCR. Real-time RT-PCR was utilized to measure the expression at the RNA level and flow cytometery was carried out to assess protein expression. Insertion of HBsAg cDNA in HEK293T genome was confirmed by PCR. The results of real-time RT-PCR illustrated that each cell expresses 2275 copies of mRNA molecule. Flow cytometry showed that compared with negative control cells, 99.9% of transfected cells express HBsAg on their surface. In conclusion, stable expression of hepatitis B surface antigen on the membrane of HEK293T provides an accurate post-translational modification, proper structure, and native folding in contrast with purified protein from prokaryotic expression systems. Therefore, these exposing HBsAg cells are practical in therapeutic, pharmaceutical, and biological sets of research.