Insulin is made up of two pieces called the A- and B-chain, shown above in blue and green respectively. These two chains are joined by disulfide bonds, which are shown in yellow. This single piece made up of the A- and B-chains is the active form of the insulin hormone. This is the form that binds the insulin receptor on fat or muscle cells in the body, singling them to take up glucose, or sugar, from the blood and save it for later.
Insulin is able to pair-up with itself and form a dimer by forming hydrogen bonds between the ends of two B-chains. These hydrogen bonds are shown above in white. Then, 3 dimers can come together in the presence of zinc ions and form a hexamer. Insulin is stored in the hexameric form in the body.
Insulin is a hormone that controls sugar metabolism and storage in the human body. The body is able to sense the concentration of glucose in the blood and respond by secreting insulin, which is produced by beta cells in the pancreas. Synthesis of human insulin in E. coli is important to producing insulin for the treatment of type 1 diabetes. The image below highlights the hydrophobic (gray) and polar (purple) parts of an insulin monomer at a pH of 7. It is believed that the hydrophobic sections on the B-chain cause insulin aggregation which initially caused problems in the manufacture and storage of insulin for pharmaceutical use.
