Production of recombinant human glucagon in the form of a fusion protein in Escherichia coli; recovery of glucagon by sequence-specific digestion.

Recombinant human glucagon was successfully produced with a high level of expression in Escherichia coli as a fusion protein with human interferon gamma. The synthetic gene was designed to release glucagon, which does not contain glutamic acid residues, from fusion protein with the Staphylococcus aureus strain V8 protease that specifically cleaves the peptide bond on the carboxyl side of the glutamic acid residue. The resulting glucagon was purified to homogeneity by a combination of C18 reverse-phase HPLC and ion-exchange HPLC. The yield of intact glucagon obtained from 11 of culture was approximately 12 mg. The structure of recombinant human glucagon was confirmed by HPLC and amino acid composition/sequence analyses.