Document Type : Research Paper
National Institute for Genetic Engineering and Biotechnology (NIGEB), Tehran, I.R. Iran.
Department of Biotechnology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, I.R. Iran.
Periplasmic expression of human growth hormone (hGH) in an arabinose-regulated Escherichia coli system
was studied, using two forms of gIII signal sequence differing from each other at position 17 (carrying
either His17 or Arg17 at position -2 in the hGH precursor). The expression of hGH by the two recombinant
plasmids was studied in the Top10 strain of E.coli. Results obtained from the expression analysis showed that the hGH expression in both of the recombinant bacteria are tightly regulated with arabinose. An optimal expression was found to occur in the medium containing 1.33 mM L-arabinose at 37°C. However, periplasmic expression of hGH occurs when the native signal sequence (His17-gIII) is applied. In the case of the bacteria carrying plasmid with the Arg17-gIII signal peptide, although the expression level was high, no mature protein could be detected under conditions tested. These data suggest for a probable effect of the -2 position in processing of the preprotein (gIII::hGH). Optimized growth and inducing conditions of the selected clone were investigated and application of a suitable signal peptide cleavage site for more efficient periplasmic production of hGH is discussed. The two recombinant plasmids presented in this work, have provided tools to study an aspect of amino acid sequence in the cleavage region on the processing and secretion of hGH.