acase@tulane.edu / G-protein coupled receptors (GPCRs) represent the largest family of receptor proteins in the living world, having approximately 800 human genes predicted. GPCRs are therapeutically relevant, as approximately 35% of all drugs on the market target them. However, these drugs can be associated with unwanted side effects, due to ubiquitous GPCR expression throughout the body, as well as GPCRs within the same family having common ligands, but varying or contradictory responses.
Although there are approximately 800 human GPCRs predicted, the high-resolution crystal structure of only 41 GPCRs are available. The first human GPCR to be crystallized was the β2-adrenergic receptor (β2AR) in 2007. Shortly thereafter an alternate crystal form of the β2AR revealed a specific cholesterol binding site between helices I, II, III and IV. From this work a cholesterol consensus motif (CCM) was established, which defined specific interactions between cholesterol and the receptor. Utilization of this CCM predicted that as many as 25% of all class A GPCRs could have a specific interaction with cholesterol at this site, including the Adenosine A2a receptor. However, the first crystal structure of the human Adenosine A2a receptor (bound to an antagonist) revealed a lipid, not cholesterol bound at the CCM. Simulations have given insight into other potential binding sites for cholesterol on the Adenosine A2a receptor’s helices 5 and 6, based on the crystal structure bound to an antagonist.
Cholesterol has been shown to modulate the activity of multiple G Protein-coupled receptors (GPCRs), yet whether cholesterol acts through specific interactions, or indirectly via modifications to the membrane is not well understood. Here we report that the activity of the adenosine A2a receptor (A2aR) is dependent on cholesterol as determined by membrane cholesterol depletion with methyl-beta-cyclodextrin (MβCD). We also tested whether a specific interaction occurs between A2aR and cholesterol, by testing the impact of mutational changes to predicted cholesterol binding sites on functional consequences.
Understanding how cholesterol modulates GPCRs could help in the design of superior drugs to target different cell types with varying membrane cholesterol concentrations, or in disease states where cholesterol homeostasis is disrupted. Additionally, the widespread use of cholesterol reducing drugs such as statins, has posed the new question of how plasma membrane cholesterol concentrations and activation of membrane embedded proteins are affected by these drugs. / 1 / Claire McGraw
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_79080 |
| Date | January 2018 |
| Contributors | McGraw, Claire (author), Robinson, Anne (Thesis advisor), School of Science & Engineering Chemical and Biomolecular Engineering (Degree granting institution) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | electronic, 129 |
| Rights | No embargo, Copyright is in accordance with U.S. Copyright law. |
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