Production of salmon calcitonin by direct expression of a glycine-extended precursor in Escherichia coli

Abstract

The export of heterologous products into the conditioned medium of an Escherichia coli culture offers the advantages of a higher product yield, an increased probability of recovering an intact recombinant protein, proper folding for biological activity, and greater stability of a secreted product. In this report, we describe the development of an optimized direct expression system, designed to maximize the extracellular accumulation of recombinant glycine-extended salmon calcitonin peptide (sCTgly). We have used dual promoters, an ompA signal sequence, co-expression of homologous secretion factor genes, and multiple gene cartridges to express the sCTgly. High-density fermentation conditions have been developed that allow for the selective secretion and accumulation of the expressed sCTgly at very high levels. Purification and in vitro enzymatic conversion by peptidylglycine alpha-amidating monooxygenase yields authentic, biologically active salmon calcitonin. This recombinant production technology is applicable to a variety of amidated peptide hormones.