task Insulin is a protein consisting of two peptide chains, an A chain and a B c
ID: 219006 • Letter: T
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Insulin is a protein consisting of two peptide chains, an A chain and a B chain, as shown in both Figure 1a and b.
Figure 1. a) Primary structure of insulin. b) 3D structure of insulin.
1. Describe the structure of insulin using Figures 1a and b.
Treatment of Type 1 diabetes can be done by medication with insulin made using genetically modified microorganisms. When the insulin molecules are formed, they are spontaneously assembled to devices of two molecules. These devices are called dimers, while a free insulin molecule is called a monomer. One Dimer of insulin molecules are inter alia held by intermolecular bonds between amino acids in the C-terminals, as shown in Figure 3a. Three dimers gather spontaneously into a hexamer, see Figure 3b.
Figure 3. a) Chemical interaction between amino acids in C-terminals from each B-chain in a dimer. The abbreviations indicate an amino acid name and position in the peptide chain. b) Hexamer of insulin composed of three dimers. In the middle you will see two zinc ions that act as cofactors.
Insulin is only active as monomer. To avoid the formation of dimers, you modify insulin enzyme so that it forms the amino acid aspartate (Asp) in place of the amino acid proline (Pro) in position 28 in the B chain.
4. Suggest why replacement of proline with aspartate can counteract the formation of dimers. Include figure 3a.
a) b) A-kzæde 1 2 3456 910 11 12 13 1415 16 17 B-kæde Glu 1 2 34567 89 10 11 12 13 14 15 16 17 18 192021 Arg 22 dly HOOG- Thr Lys Pro Thr Tyr Phe Phe 3029?27262524·MakeeExplanation / Answer
Ans.1). Insulin is a glucose level regualting pepetide hormone, produced by pancreatic beta-cells. Insulin is made up of two polypetide chains, A and B, whcih are linked together by disulfide linkage. Generally, A chain is made up of 21 amino acid residues and B chain consists 30 amino acid residues. Insulin shows three disulfide linkages, two between A and B chains and one within the Acahin. Insulin can take dimer form in the solution with the help of hydrogen bonding between C-ends of B chains and these dimers can form insulin hexamer in the presence of zinc.
4). Insulin shows its activity only in monomeric form. As discussed above, insulin forms dimers with the help of hydrogen bonding between C-termini of B polypeptides. Proline at 28th positiono B chain is critical for this dimerization. substitution of this proline with aspartate affects the dimerization of insulin, due to increased charge repulsion between two aspartate residues of two different B chains.
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