Recombinant Somatostatin

RECOMBINANT SOMATOSTATIN

Somatostatin, also known as the ‘antigrowth hormone’, modulates the action of growth hormone and is frequently used to treat acromegaly (uncontrolled bone growth). Being a very small peptide, the gene coding for it can easily be chemically synthesized and cloned into a suitable expression vector. As E. coli tends to degrade small peptides, the generation of a β-galactosidase–somatostatin fusion protein prevents this degradation. Furthermore, as with insulin, the absence of methionine residues in the somatostatin amino acid sequence allows the insertion of a methionine codon in the junction between β-galactosidase and the somatostatin gene. This enables the subsequent cleavage with cyanogen bromide of the recombinant hormone purified from E. coli. Thesomatostatin fusion protein prevents this degradation. Furthermore, as with insulin, the absence of methionine residues in the somatostatin amino acid sequence allows the insertion of a methionine codon in the junction between β-galactosidase and the somatostatin gene. This enables the subsequent cleavage with cyanogen bromide of the recombinant hormone purified from E. coli. The strategy used to generate recombinant somatostatin is shown in Figure 25.9.