Bacterial production and structure-function validation of a recombinant glucagon peptide

Glucagon, a peptide hormone clinically used to treat acute hypoglycemia in diabetes patients, is readily degenerated by undergoing fibrillation under pharmaceutical conditions. Since glucagon is employed as a typical model system for structural investigation of amyloid fibril formation of proteins, production of recombinant glucagon is in demand to facilitate mutagenesis and isotope labeling for nuclear magnetic resonance (NMR) studies. In this study, we established a method to produce recombinant glucagon in Escherichia coli. Recombinant plasmids were constructed to express a maltose-binding protein-fused glucagon, which was cleaved by factor-Xa protease to yield glucagon peptide without any N-terminal extra residues. The final product was clearly identified and characterized by immunoblotting, mass spectrometry, circular dichroism spectroscopy, and backbone NMR assignments of the [13C/15N] isotope-enriched sample. Cellular activity of the recombinant glucagon in hepatocytes was confirmed by monitoring characteristic gene expressions. Site-directed mutagenesis was successfully performed using our recombinant production system. Our bacterial production system and the recombinant glucagon not only provide an economical route of glucagon manufacturing, but also enable NMRbased structural investigation of glucagon fibrillation.