Insulin is the most used of all therapeutic recombinant proteins..
Insulin is secreted by the pancreas. Absent or inadequate secretion leads to diabetes.
The key sign of diabetes is sustained increase, beyond normal levels, of blood glucose.
Initially extracted from bovine or pig pancreas, Insulins used nowadays are more and more of the "recombinant" type; produced by recombinant DNA technology, utilizing E. coli or yeast (Saccharomyces) fermentation.
Human insulin has 2 peptide chains : A (21 amino acids) and B (30 amino acids). These chains are linked by disulfide bridges (S S on the drawing).
Genetic engineering can allow slight modifications of the molecule to increase its duration of action. Lysine B29 can thus be interverted with Proline B28. Asparagine A21 can be replaced by a Glycine.
On January 26, 2006, FDA approved for the first time a human insulin inhalation powder, this one being a non modified insulin.