Expression of human parathyroid hormone-(1-84) in Escherichia coli as a factor X-cleavable fusion protein.

Recombinant human parathyroid hormone (hPTH)-(1-84) was obtained from Escherichia coli using a cleavable fusion protein strategy. The fusion protein contains residues 1-138 of human growth hormone as the amino-terminal region and residues 1-84 of hPTH as the carboxyl-terminal region. A 7-residue linker containing the recognition/cleavage sequence of the site-specific blood coagulation protease activated factor X (factor Xa) joins the two regions. Intact hPTH-(1-84) is released from this fusion protein by cleavage in vitro with factor Xa. The fusion protein was produced at a high level and formed inclusion bodies which allowed it to be easily purified by low speed centrifugation, with a yield of approximately 50 mg/liter of culture. After factor Xa cleavage and high performance liquid chromatography purification, highly purified hPTH was obtained, with a final yield of 1.5-3 mg/liter. Physical and biological characterization of the purified hormone demonstrated that it was intact and active hPTH-(1-84).