A method for the high-level expression of a parathyroid hormone analog in Escherichia coli

A recombinant parathyroid hormone analog, rPTH(1-34*), was obtained from Escherichia coli using a gene polymerization strategy. The PTH gene polymer contains up to 8 copies of the gene, each separated by a cleavable linker. The polymer was expressed at very high levels and formed inclusion bodies which could be easily isolated by low-speed centrifugation. A polyhistidine leader peptide allows rapid purification via nickel chelation chromatography of the PTH polymer solubilized from the inclusion bodies. Yields of greater than 500 mg/liter have been obtained. After isolating the polymer, monomeric rPTH(1-34*) is released from the polymer by chemical cleavage with cyanogen bromide. Following cyanogen bromide cleavage and high-performance liquid chromatography purification, highly purified, biologically active rPTH(1-34*) is obtained at a yield of approximately 300 mg/liter. This is a general strategy for the high-level production of a variety of peptides and small proteins.