Factors affecting the synthesis of the n-terminal methionine-free molecule of recombinant human interleukin-2 by Escherichia coli

Escherichia coli harboring the gene encoding human interleukin-2 (IL-2) produces a mixture of two recombinant IL-2 species: one with the amino-terminal alanine (rIL-2) and the other having an additional methionine residue at the amino terminus (Met-rIL-2). Ways to increase the amount of rIL-2 and its proportion to the total IL-2 were tried. Among E. coli K-12 derivatives, N4830 was an effective producer of recombinant IL-2. The production of the mixture was greatly increased by optimizing the medium ingredients or culture conditions. However, the percentage of rIL-2 in the product decreased almost linearly with an increase of the total production of recombinant IL-2 and was less than 10% under optimal culture conditions. By adding 4.1 × 10⁻⁵ M maganese and 7.4 × 10⁻⁵ M ferric ions to the medium, we succeeded in raising the percentage of rIL-2 to 50% without any decrease of the total production.