Research article
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Abstract
We constructed a series of hybrid plasmids which directed the synthesis of different human growth hormone (hGH) precursor sequences in Bacillus subtilis. In addition to the 191 amino acids of the hormone, the precursors had in common an amino-terminal extension characterized by the presence of a methionine at position 1 and of the tetrapeptide Ile-Glu-Gly-Arg preceding the first residue (Phe) of hGH.
The sequence between the methionine and the tetrapeptide was specific for each precursor and, because of the presence of charged residues, conferred particular properties to the molecules. Long homopolymeric tail-containing precursors such as MRRRRRRIILM-IEGR appeared insoluble whereas shorter sequences of the type MRR-IEGR and MEELM-IEGR augmented the solubility of the precursors with respect to Met-hGH. The soluble precursors could be easily purified from the bulk proteins taking advantage of the charged residues present on the N-terminal tail.
After purification, the natural hGH was obtained by treating the precursors with the protease Factor Xa which cleaves after the arginine residue of the tetrapeptide IEGR.
A protocol for the production and purification of authentic hGH from a strain expressing one of these soluble precursors is reported.
Keywords
Human growth hormone
;
Bacillus subtilis
;
Factor Xa
;
Purification
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