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Introduction
The insulin receptor is a vital proponent of cellular function. It plays a key role in a variety of cellular pathways including glucose homeostasis, regulation of lipid, protein, and carbohydrate metabolism, gene expression, and even modulation of brain neurotransmitter levels. This page focuses specifically on the insulin receptor's role in glucose homeostasis.
Structural Highlights
Figure 1. The Coolest Image of this Protein!
Function
The insulin receptor's function in regards to glucose homeostasis is to begin the signaling pathway that will eventually move glucose transporters to the cell surface which will allow glucose to passively defuse into the cell. The glucose receptor is inactive in the absence of insulin. When insulin does bind to the receptor, it undergoes a conformation change, activating it. Once activated, the intracellular Beta subunits autophosphorylate, and downstream signaling begins by the phosphorylation of the Insulin Receptor Substrate (IRS).
Conformation Change
The insulin receptor has two conformations, an active and inactive state. The inactive form predominates in low-levels of circulating insulin, whereas the active conformation is seen when insulin binds to any of the 4 receptor sites. The inactive conformation resembles an inverted V, and the active conformation resembles a T. Upon the binding of insulin to any of the four binding sites, the conformation change will begin, causing the Beta subunit's tyrosine kinase domains to move close together, allowing them to autophosphorylate. This autophosphorylation is what activates the insulin receptor and allows it to participate in further downstream signaling pathways.
Relevance
Disease
One of the most common diseases involving the insulin receptor is diabetes mellitus. There are two types of diabetes- which are referred to as type 1 and type 2 diabetes. Type 1 diabetes is classified as "insulin dependent" and is characterized by an inability for the body to produce insulin. This is most often the result of damage or insufficiency in the Islets of Langerhans in the pancreas. Type 2 diabetes is classified as "insulin independent" and is the result of the body producing insufficient amounts of insulin, or not responding to the insulin. This often occurs because of high blood-glucose levels.
Treatment of Diabetes with Insulin
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