Use of a Derivative of Escherichia coli BL21(DE3) for Efficient Production of Three Different Recombinant Proteins

Plasmid instability and growth inhibition of plasmid-bearing cells after induction were encountered when E. coli BL21(DE3) was used as host for the production of antihuman ovarian carcinoma x antihuman CD3 single-chain bispecific antibody (AhOCxAhCD3), human soluble B lymphocyte stimulator fused with thioredoxin (Trx-hsBLyS) and human parathyroid hormone fused with thioredoxin (Trx-hPTH). A derivative of BL21(DE3), namely, BLRM(DE3), isolated and showing superiority in AhOCxAhCD3 production in our previous work, was further used here for more efficient production of these three different recombinant proteins. By using BLRM-(DE3) as host, the simplified one-stage fermentation process was developed, which was more labor-saving and yielded AhOCxAhCD3, comparable to that of the traditional two-stage fermentation process. Also, the plasmid stabilities and production yields of Trx-hsBLyS and Trx-hPTH were dramatically improved by the application of BLRM(DE3) instead of BL21-(DE3). A high Trx-hsBLyS yield (about 3.5 g/L) was obtained, which was more than twice as much as that of the recombinant BL21(DE3) strain. The Trx-hPTH yield was improved from about 700 mg/L to 1 g/L. These results further showed the superiority of BLRM(DE3) to BL21-(DE3) and suggested its effectiveness for other BL21(DE3)/pET heterologous protein expression systems, which encounter similar problems.