Cytoplasmic production of soluble and functional single-chain Fv-Fc fusion protein in Escherichia coli

Abstract

We describe the soluble production of a mouse anti-bovine ribonuclease A single-chain variable fragment (scFv) fused with the Fc region of human IgG1 in Escherichia coli. Two production systems, secretory production using a pelB signal peptide and cytoplasmic production in a trxB/gor double mutant strain with an oxidizing cytoplasm, were investigated for efficient production of soluble and functional scFv-Fc fusion protein. Antigen-binding activity was observed in both systems but almost all of the scFv-Fc that was expressed formed insoluble aggregates. Hence, the co-expression of molecular chaperones was examined. Co-expression of GroEL/GroES showed a 4.6-fold increase in antigen-binding activity in the cytoplasmic production system but not in the secretory system. By contrast, the other two chaperones, DnaK/DnaJ/GrpE and trigger factor, had no effect in either production system. The protein solubility was also improved markedly by the co-expression of GroEL/GroES and approximately 70% of the 3A21 scFv-Fc protein was soluble. A practical productivity of more than 10mg/L was achieved with a simple batch shake-flask culture. These results indicate that the E. coli cytoplasmic production system with oxidizing cytoplasm and molecular chaperones might be one of the choices for the soluble production of scFv-Fcs and other Fc fusion proteins.