Shaperone-Dependent Optimization of Expression in E. coli and Purification of Soluble Recombinant Lipid A Phosphatase LpxE from Francisella tularensis

Lipid-1a-phosphatase LpxE cleaves the phosphate group in the first position of lipid A of lipopolysaccharide in Gram-negative bacteria, which reduces toxicity and reactogenicity of bacterial endotoxin while maintaining its immunogenicity. Treatment with these enzymes in preparations of recombinant proteins obtained in bacterial producers, for example, in E. coli, may find application in the purification techniques of various pharmaceutical substances, primarily various protein components of vaccines. This work is devoted to the creation of an efficient method for obtaining an F. tularensis LpxE soluble protein in a heterologous expression system based on E. coli. Optimization of the bacterial production of LpxE enzyme is achieved by creating a SUMO-LpxE chimeric protein in which the SUMO polypeptide acts as a folding catalyst and an affinity target carrier for purifying the expression product. An additional increase in the level of synthesis of LpxE and reduction of its toxicity for a bacterial strain is achieved against the background of superproduction of bacterial periplasmic chaperones encoded by an auxiliary low copy plasmid. Subsequent chromatographic purification of the target recombinant protein involves the use of affinity metal chelate chromatography and a SUMO protease cleavage step of the SUMO peptide carrying the His6 N-terminal peptide with the reduction of natural primary structure of the enzyme. The developed method makes it possible to obtain a highly purified active enzyme LpxE F. tularensis with a yield of 0.26 g/L of bacterial culture without fermentation.