A time-efficient workflow to purify a library of alanine mutants of surface-exposed residues of the domain III of the envelope protein of dengue virus serotype 1.

Dengue complex is formed by four viral serotypes that cause the disease of the same name. Dengue is the arthropod-borne disease with the highest incidence worldwide. The envelope glycoprotein comprises three structural domains. The domain III (DIII) induces neutralizing antibodies and is involved in the interactions with soluble plasma factors from human host. Recombinant DIII proteins have been used as analytical tools for the characterization of virus-host interactions and have been evaluated as sub-unit vaccines. Here, we report a purification procedure of recombinant DIII protein and seventy-four alanine mutants refolding by size exclusion chromatography that allows obtaining highly homogeneous protein preparations and suitable for efficient purification and folding check. Four positions are identified that significantly affect either the protein expression or folding of recombinant DIIIE1, K310, G304, D330 and P332.

An engineered SARS-CoV-2 receptor-binding domain produced in Pichia pastoris as a candidate vaccine antigen.

Developing affordable and easily manufactured SARS-CoV-2 vaccines will be essential to achieve worldwide vaccine coverage and long-term control of the COVID-19 pandemic. Here the development is reported of a vaccine based on the SARS-CoV-2 receptor-binding domain (RBD), produced in the yeast Pichia pastoris. The RBD was modified by adding flexible N- and C-terminal amino acid extensions that modulate protein/protein interactions and facilitate protein purification. A fed-batch methanol fermentation with a yeast extract-based culture medium in a 50 L fermenter and an immobilized metal ion affinity chromatography-based downstream purification process yielded 30-40 mg/L of RBD. Correct folding of the purified protein was demonstrated by mass spectrometry, circular dichroism, and determinations of binding affinity to the angiotensin-converting enzyme 2 (ACE2) receptor. The RBD antigen also exhibited high reactivity with sera from convalescent individuals and Pfizer-BioNTech or Sputnik V vaccinees. Immunization of mice and non-human primates with 50 µg of the recombinant RBD adjuvanted with alum induced high levels of binding antibodies as assessed by ELISA with RBD produced in HEK293T cells, and which inhibited RBD binding to ACE2 and neutralized infection of VeroE6 cells by SARS-CoV-2. Additionally, the RBD protein stimulated IFNγ, IL-2, IL-6, IL-4 and TNFα secretion in splenocytes and lung CD3+-enriched cells of immunized mice. The data suggest that the RBD recombinant protein produced in yeast P. pastoris is suitable as a vaccine candidate against COVID-19.

Osmoregulated TAQ polymerase gene expression in Escherichia coli.

The Thermus aquaticus DNA Polymerase I (Taq Pol I) gene was cloned into the pOSEX4 plasmid under the osmo-inducible promoter proU and subsequently expressed into the Escherichia coli MKH13 strain. The suitability of the enzyme in polymerase assays was determined in standard 35S dATP incorporation tests and by PCR. The Taq Pol I expression in this system, which is under the control of the osmotic pressure in the growth medium, was analyzed in different media and in different sodium chloride concentrations. A study of the osmolarity effects in the growth of the strain and in Taq Pol I expression shows that an increase in sodium chloride concentration limits the growth. At 0.25 M of NaCl maximum activity was observed; at higher values of osmolarity, we found an unexpected decline of activity. This is the first report of using the pOSEX vector for the expression of an heterologous protein and it is very advantageous to make a regulated, non toxic, simple and cost-effective manner of induction in a biotechnology process using just NaCl or other non-permeable osmolyte.