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Bio-Similar protein variants of Human Insulin

    Bio-active Insulin comprises two polypeptides, Chain A (21 amino acids) and Chain B (30 amino acids), transcribed from a single gene locus, and processed post-translation to remove a leading Signal Peptide and an intervening C chain. The NH₃ end of both chains is shown at the left, and the amino acid residues are numbered from that end. The chains are held together by two Cys:Cys bridges between chains (A7 + B7, and A21 + B19), and a third within Chain A (A6 + A11) (see inset 3D model).

    In the first applied bio-engineering experiment, human Insulin was cloned separately as the two A & B chains, which spontaneously assembled into the 3D form when combined in vitro. This commercial product had the same amino acid sequence as native Insulin, and was marked by Eli Lilly as Humulin [upper left corner]. Humulin has the advantage of not being sourced from animal tissue, such as pig and bovine pancreases, so as to avoid an immune responses to animal insulins with slightly different amino acid sequence. Humulin still had the problems of animal-sourced insulin, including requirements for refrigeration and frequent injection. Based on knowledge of the structural biochemistry of the insulin molecule, SNP variants have been engineered into the plasmid cloning system (see Table upper right, shown as red replacement residues in the amino acid sequences below). These substitutions modify the qualities of insulin for specific therapeutic applications, typically speed of bio-activation and tissue solubility. Insulin Lispro (marketed as Humalog) is mobilized more rapidly than Humulin in tissue, so as to provide a faster response to hypoglycemia. Insulin Aspart (Novolog) behaves similarly, and may be more effective on Type I (Juvenile) Diabetes. Insulin Glulisine (marketed as Apidra) has two modified amino acid residues in Chain B, which decreases the affinity of the chain for itself and thus avoids the tendency to form polymers. In contrast to the others, Glargine (marketed as Rezvolar and Basaglar) has two added Arg residues at the C-terminus of Chain B, which makes it less soluble in tissue, and slower release allows longer intervals between injections.Therapeutic regimes may combine faster- & slower release Insulin types

    HOMEWORK: Identify the SNP variants necessary to produce the bio-similar insulin molecules from the original human insulin / Humulin DNA sequence,