Using L-arabinose for production of human growth hormone in Escherichia coli, studying the processing of gIII::hGH precursor

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 His 17 or Arg 17 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 (His 17 -gIII) is applied. In the case of the bacteria carrying plasmid with the Arg 17 -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.