Soubor:GPCR cycle.jpg

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Obrázek + English: Cartoon depicting the GPCR-G-protein activation/deactivation cycle. In the resting state the receptor may be found associated with a heterotrimeric G-protein with GDP bound to its alpha subunit. Agonist binding to the GPCR induces a cascade of conformational changes first in the receptor and then in the bound G-alpha subunit of the G-protein. This results in release of GDP which is soon replaced by GTP. The cell maintains a 10:1 ratio of cytosolic GTP:GDP so exchange for GTP is ensured. GTP-bound G-alpha takes yet another conformation that has low affinity for the GPCR as well as the Beta-Gamma complex, so all three dissociate from one another. GTP-G-alpha and the G-beta/gamma complex then go on to allosterically modulate the activies of various downstream effector proteins, but diffusion is usually limited to the membrane surface due to the presence of palmitoyl and a GPI-anchor, respectively. The GTP-binding site of G-alpha is also capable of hydrolyzing GTP to GDP, albeit at a relatively slow rate. This rate can be increased by binding to various GTPase activating Proteins (GAPs) such as those of the RGS family. Many effector molecules modulated by G-alpha also have GAP activity. Upon GTP hydrolysis the G-alpha subunit is rendered inactive and once again may bind G-beta/gamma and form a heterotrimeric G-protein, which will often be found associated with an unliganded GPCR.

• Date: 23 June 2010

+ pochází z Wikimedia Commons, kde má status – Creative Commons Attribution-Share Alike 3.0 Unported (autor: Repapetilto)

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	Datum a čas	Náhled	Rozměry	Uživatel	Komentář
současná	1. 4. 2013, 14:41		1 667×1 250 (396 kB)	Sysop (diskuse | příspěvky)	(BUNDESA117)

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