Formation of soluble recombinant proteins in escherichia coli is favored by lower growth temperature

Human interferon-α2 (IFN-α2), an 18 kD, acidic protein, human interferon-γ (IFN-γ), a 17 kD, basic protein, and the interferon-induced murine protein Mx (72 kD) were all found in aggregates when produced in genetically engineered strains of E. coli grown at 37°C. However, at a growth temperature of 23-30°C, 30-90% of the recombinant protein was soluble. The temperature effect was not directly dependent on the concentration of the protein and was observed for several E. coli strains and for different plasmid constructions. Lysates of non-transformed E. coli grown at either temperature rendered initially soluble human recombinant IFN- a2 insoluble at 37° but not at 0° or 30°C. Insolubilization was not abolished by nuclease treatment, and may involve sulfhy- dryl group shuffling, as sulfhydryl reducing agents added to a mock lysate gave a similar temperature dependent precipitation.