Optimisation of the mRNA secondary structure to improve the expression of interleukin-24 (IL-24) in Escherichia coli

The expression, purification, and functional evaluation of the novel tumor suppressor fusion protein IL-24-CN

Interleukin-24 (IL-24) can specifically induce apoptosis in a broad range of cancer cells without harming normal cells. The interaction of contortrostatin (CN) with integrins on angiogenic vascular endothelial and tumor cells is modulated by the RGD motifs that can significantly inhibit metastasis and angiogenesis. To achieve superior therapeutic efficacy by combining anti-metastasis with tumor-selective apoptosis activity, CN was fused at the C-terminus of IL-24 with a flexible linker (G₄S)₂, and the recombinant IL-24-CN was expressed in Escherichia coli as a Thioredoxin (Trx)/IL-24-CN fusion protein. The target protein was purified using nickel affinity chromatography. Furthermore, we simplified the purification process by purifying Trx-IL-24-CN and cleaving the Trx tag in one step. The final yield of IL-24-CN was 27.6 mg/L based on flask fermentation. In vitro activity assay demonstrated that the recombinant IL-24-CN could more effectively suppress tumor growth and induce apoptosis of melanoma cells. Scratch and transwell assays suggested that IL-24-CN strongly reduced the migration and invasion behavior of melanoma cells. Immunofluorescence analysis and cell adhesion assay showed that CN could evidently improve the tumor inhibition capability of IL-24 by enhancing the affinity of recombinant protein toward cancer cells. In summary, a highly efficient strategy was developed for producing the bioactive IL-24-CN from prokaryotic cells, supporting IL-24-CN in melanoma therapy.Key points• Efficient heterologous production of recombinant IL-24-CN in E. coli using Trx fusion strategy.• Improved tumor growth suppression and apoptosis induction potency of IL-24-CN.• Enhanced cell adhesion ability of IL-24-CN in cancer cells.

High-efficiency expression and secretion of human FGF21 in Bacillus subtilis by intercalation of a mini-cistron cassette and combinatorial optimization of cell regulatory components

Background

Recombinant human Fibroblast growth factor 21 (rhFGF21) is an endocrine hormone that has profound effects on treatment of metabolic diseases. However, rhFGF21 is prone to form inclusion body when expressed in bacteria, which results in, the downstream process of purification of bioactive rhFGF21 is time-consuming and labor intensive. The aim of this work is to explore a new method for improving the soluble expression and secretion level of rhFGF21 in B. subtilis.

Results

A codon optimized rhFGF21 gene was expressed under the control of a strong inducible promoter P_malA in B. subtilis. A mini-cistron cassette (from gsiB) was located upstream of rhFGF21 in expression vector (pMATEFc5), which could reduce the locally stabilized mRNA secondary structure of transcripts and enhance the efficiency of translation initiation. Then various chaperones were further overexpressed to improve the expression efficiency of rhFGF21. Results showed that overexpression of the chaperone DnaK contributed to the increase of solubility of rhFGF21. Moreover, an extracellular proteases deficient strain B. subtilis Kno6cf was used to accumulate the secreted rhFGF21 solidly. In addition, eleven signal peptides from B. subtilis were evaluated and the SP_dacB appeared the highest secretion yield of rhFGF21 in B. subtilis. Finally, the combinatorial optimized strain achieved an about ninefold increase of the soluble rhFGF21 production after 24 h of flask fermentation in comparison with the initial production strain.

Conclusion

This work provided a comprehensive strategy for secretory expressing the heterologous protein rhFGF21 in B. subtilis. To our knowledge, this is the first report of the highly efficient production of rhFGF21 in B. subtilis and this approach may provide some suggestions for heterologous proteins production in B. subtilis.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1066-4) contains supplementary material, which is available to authorized users.

The mechanisms of Ag85A DNA vaccine activates RNA sensors through new signal transduction

Low immunogenicity is one of the major problems limiting the clinical use for DNA vaccines, which makes it impossible to obtain a strong protective immune response after vaccination. In order to explore whether Ag85A DNA vaccine could mount more efficiently protective immune response through new RNA sensor and its signal transduction pathway of antigen presentation we designed and synthesized Ag85A gene fragment containing multiple points mutations and transfected the gene fragment into the dendritic cell line (DC2.4) by CRISPR/Cas9. Subsequently, we focused on the changes of RNA sensors RIG-I, Mda-5, and the downstream adaptors MAVS, IRF3, IRF7 and IFN-β. The results indicated the significant increases in the mRNA and protein expression of RNA sensors RIG-I, Mda-5 and related adaptors MAVS, IRF3, IRF7, and IFN-β in the mutant DC 2.4 cells. The flow cytometry results demonstrated that the expression of MHC II on the surface of DC 2.4 significantly increased when compared with that in control. Therefore, it is suggested that Ag85A mutant DNA could release immunogenic message through RNA sensors and related adaptors via non protein pathway. There is at least one RNA signal transduction pathway of Ag85A DNA in DC2.4 cell. The work provides a new mode of action for nucleic acid vaccine to improve immunogenicity and meaningful data for the better understanding of the mechanisms of DNA vaccine.

Efficient Extracellular Expression of Metalloprotease for Z-Aspartame Synthesis

Metalloprotease PT121 and its mutant Y114S (Tyr114 was substituted to Ser) are effective catalysts for the synthesis of Z-aspartame (Z-APM). This study presents the selection of a suitable signal peptide for improving expression and extracellular secretion of proteases PT121 and Y114S by Escherichia coli. Co-inducers containing IPTG and arabinose were used to promote protease production and cell growth. Under optimal conditions, the expression levels of PT121 and Y114S reached >500 mg/L, and the extracellular activity of PT121/Y114S accounted for 87/82% of the total activity of proteases. Surprisingly, purer protein was obtained in the supernatant, because arabinose reduced cell membrane permeability, avoiding cell lysis. Comparison of Z-APM synthesis and caseinolysis between proteases PT121 and Y114S showed that mutant Y114S presented remarkably higher activity of Z-APM synthesis and considerably lower activity of caseinolysis. The significant difference in substrate specificity renders these enzymes promising biocatalysts.

Quantitative relationship between the mRNA secondary structure of translational initiation region and the expression level of heterologous protein in Escherichia coli

Translational efficiency in Escherichia coli is strongly influenced by mRNA secondary structure of translational initiation region (TIR). We have previously reported that the expression of heterologous protein is directly related to the minimal folding free energy (ΔG) of the local secondary structure. However, identifying biologically relevant maximum and minimum levels of expression, or exploring the optimal level between them, is a key to successful optimization of heterologous protein expression. To systematically search a large range of the ΔG of TIR, we now present a quantitative analysis of the relationship between expression level and these ΔGs. The ΔG of TIR in green fluorescent protein is found to be linearly correlated with the fluorescence intensity over a range of tenfold change. The result demonstrates that the increasing ΔG of TIR can enhance the expression level linearly with no threshold or plateau.