Johnson's Monday Lab Sandbox for Insulin Receptor
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Insulin Receptor
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Purpose of ReceptorInsulinStructureThe insulin receptor is a heterotetramer which resides in the plasma membrane of insulin target cells. The ectodomain is made up of two alpha subunits and two beta subunits. Each alpha subunit contains two leucine rich domains and a cysteine rich domain. Each beta subunit is made up of three fibronectin type III domains. The insulin receptor extends intracellularly from the beta subunits of the ectodomain by way of a transmembrane alpha helix. The intracellular domain contains two tyrosine kinase domains. How Insulin BindsThe insulin receptor unit has four separate sites for the insulin molecule to bind to. There are two pairs of two identical binding sites referred to as 1 and 1' and then 2 and 2'. The insulin molecules bind to these sites mostly through hydrophobic interactions. Despite a majority of the interactions being similar, sites 1 and 1' have a higher binding affinity than sites 2 and 2' due to site one having a larger surface area (706 square angstroms) exposed for insulin to bind to compared to site 2 (394 square angstroms)[3]. It was found that at least three insulin molecules would have to bind to the receptor for the receptor to take on its active “T-state” conformation [3]. The difference between the fully bound state with four insulins and the three insulin bound state is minimal compared to the difference between two and three insulins bound [3]. Conformational ChangesType II DiabetesReferences
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