Colicin A lysis protein promotes extracellular release of active human growth hormone accumulated in Escherichia coli cytoplasm

The colicin A lysis protein (Cal) was used to direct the extracellular release of recombinant proteins produced in Escherichia coli. The cal gene, under the control of its inducible promoter, was introduced into an expression vector encoding the human growth hormone devoid of its signal sequence (Met-hGH). Cal and Met-hGH were simultaneously expressed at two different levels of Met-hGH induction. The results indicate that Cal causes the excretion of non-aggregated Met-hGH from the cytoplasm to the culture medium and that the Met-hGH is correctly folded since the released Met-hGH is antigenically indistinguishable from the authentic mature hGH and is biologically active in binding to specific receptor sites.