Genetically Engineered Insulin: Production of Human Insulin

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BIOTECHNOLOGICAL APPLICATIONS IN MEDICINE

• The recombinant DNA technological processes have made great impact in the area of healthcare by mass production of safe and more effective therapeutic drugs.
• Further, the recombinant therapeutics do not induce unwanted immunological responses.
• Now about 30 recombi-nant therapeutics have been approved for human use all over the world.
• In India, 12 of these are presently being marketed.

Genetically Engineered Insulin

• Role of Sharpy-Shafer, Banting, Best and Macleod.
• Sharpy-Shafer (1916) first expressed the opinion that diabetes is caused by failure of the islets of pancreas to secrete a substance named by him as insulin.
• Insulin is secreted by the Beta cells of the islets of Langerhans of the pancreas.
• In 1921, Banting and Best succeeded in preparing a pure extract of insulin from the pancreatic islets of a dog with the help of Macleod.
• Banting and Macleod won the 1923 Nobel Prize in Medicine or Physiology.
• They demonstrated that administration of insulin could cure diabetes in human beings.
• Earlier, insulin for curing diabetes used to be extracted from pancreas of slaughtered pigs and cattle.
• This insulin is slightly different from human insulin and brings about some undesirable side effects such allergy.

Structure of Insulin.

• Human insulin is made up of 51 amino acids arranged in two polypeptide chains, A having 21 amino acids and B with 30 amino acids.
• The two polypeptide chains are interconnected by two disulphide bridges or S-S linkages.
• An S-S linkage also occurs in A chain.
• The hormone develops from a storage product called pro- insulin.
• Proinsulin has three chains, A, B and C.
• C-chain with 33 amino acids is removed prior to insulin formation.
• Bacteria can not be made to synthesise insulin from its gene because of the presence of introns.
• Bacteria do not possess enzymes for removing intron mediated transcription.

How Insulin is Synthesized ?

• As stated earlier insulin is produced by the Beta cells of the islets of Langerhans of the pancreas.
• The gene for this protein synthesis is located on chromosome 11.
• In mammals, including humans, insulin is synthesized as a pro-hormone (like a proenzyme, the prohormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide.
• This C peptide is not present in the mature insulin and is removed during maturation into insulin.
• The main challenge for production of insulin using rDNA technique was getting insulin assembled into a mature form.
• In 1983, Eli Lilly an American company, first prepared two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of Escherichia coli to produce insulin chains. Chains A andB were produced separately, extracted and combined by creating disulfide bonds to form human insulin (humulin).
• Molecular structure of insulin was worked out by Sanger.Tsan synthesised human insulin for the first time.
• Production of Human Insulin. It involves essentially the following stages:

• Isolation of Donor or DNA segment. A useful DNA segment is isolated from the donor organism.
• Formation of Recombinant DNA (rDNA). Both the vector and donor DNA seg- ments are cut in the presence of restriction endonuclease.
• In the presence of ligase DNA segments of both are joined to form rDNA.
• Production of Multiple Cop- ies of rDNA.
• Next step in the process is production of multiple copies of this recombinant DNA.
• Introduction of rDNA in the recipient organism.
• This rDNA is inserted into a recipient organism.
• Screening of the trans- formed cells.
• The recipient (host) cells are screened in the presence of rDNA and the product of donor gene.
• The transformed cells are separated and multiplied, an economical method for its mass production.
• The various steps and their sequence for the pro- duction of human insulin are depicted in.
• Dr Saran Narang, a scientist of Indian origin, working in Ottawa, Canada was involved in cloning of insulin gene.
• The most famous of the dogs Banting and Best used was one called "Marjorie".
• The first patient of diabetes to be administered insulin was 14- year old Leonard Thompson. Insulin can not be orally admin- istered to diabetic patient be- cause it degrades in the alimentary canal.
• Banting was born on November 14th, Novmember is observed as "Diabetic Day"
• In 1982 insulin (Eli Lilly's Humulin) was the first product made genetically engineered bacteria to be approved for use in Britain and the U.S.A. 1891 hence 14th.

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