Preparation of a recombinant ribonuclease inhibitor in E. coli for use in mRNA synthesis in vitro

Technologies underlying the production of synthetic mRNAs in vitro have significantly expanded the possibilities for research and therapeutic use of this class of molecules. The flagship application area has been the niche of mRNA vaccines, but this class of therapeutic molecules has the potential to be applied in a much broader range of situations. The process of in vitro production of artificial RNA molecules is based on an enzymatic synthesis reaction, one of the components of which is a ribonuclease inhibitor. This protein protects synthesized RNA from attacks by ribonucleases and prevents degradation of the molecules, which is critically important for RNA. Eukaryotic ribonuclease inhibitor synthesized as a recombinant protein in the cells of E. coli bacteria is the most common choice. However, the structure of this protein makes it a difficult product to make in bacteria. This study aimed to test the production of a recombinant ribonuclease inhibitor in various strains of E. coli, and to show the effect that helper polypeptides and cellular chaperones have on this process. Using genetic engineering approaches, we constructed plasmids, from which chimeric ribonuclease inhibitor molecules and helper polypeptides were produced. The influence of various components on solubility of the target recombinant protein was assessed with the help of densitometry, to which we have subjected products of the PAGE electrophoresis. It was determined that combinations of a vector with a strong promoter for the expression of the RNH1 ribonuclease inhibitor gene and helper polypeptides MBP and TIG against the background of increased expression of cellular chaperones dnaK, dnaJ, grpE give the target product yield of 45 mg/l and 60 mg/l, respectively. The selected conditions allow large-scale production of this protein for further use in in vitro RNA synthesis in the context of production of medicines.