High yield expression and purification of human endothelin-1

A DNA construct encoding human big endothelin (Big ET) preceded by the factor Xa protease recognition site (Ile-Glu-Gly-Arg), fused in frame to the maltose binding protein sequence, has been introduced in DH5-alpha cells. The fusion product (MBP-Big ET) was expressed at a concentration close to 100 micrograms/ml of culture broth and constituted approximately 50% of the total protein content. Crude cell extracts containing the fusion product have been directly treated with trypsin under mild denaturing conditions in order to release big endothelin (1-37) from the adduct. Cleavage yield of the MBP-Big ET adduct was close to 70%. Big ET(1-37) was separated from unrelated peptides derived from the tryptic digest of the bacterial extract by affinity chromatography. The affinity column was prepared by immobilizing a protease resistant peptide ligand able to recognize Big ET with sufficient affinity, selectivity, and specificity. From the affinity step (recovery, 90%), recombinant Big ET(1-37) was obtained with a purity close to 80%. The affinity-purified recombinant product was then digested with alpha-chymotrypsin in order to release endothelin (1-21), which was then purified by RP-HPLC. With this two-step purification protocol, 3 micrograms of endothelin was recovered from 1 ml of bacterial broth, with a purity close to 95%.