DernburgLecture5_2-8-10_forprinting

DernburgLecture5_2-8-10_forprinting - Signaling through...

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Trimeric G-proteins are usually tethered to the plasma membrane by both their ! and " subunits. The ! subunit is the GTPase. Activation by a GPCR results in release of GDP and binding of GTP, which leads to splitting of the trimer and activation of both the ! and #" subunits. Signaling through G-Proteins 1 Monday, February 8, 2010 The switch-like behavior of G-proteins arises from conformational changes that occur upon GTP binding or hydrolysis 2 Monday, February 8, 2010 The amount of the G-protein in the ON state is regulated by GEFs (Guanine nucleotide exchange factors), which promote release of GDP and binding of GTP, and GAPs (GTPase activating proteins), which promote the hydrolysis of GTP to GDP. G-Proteins, a.k.a. GTPases, come in 2 flavors: “Small” (or monomeric), and “large” (trimeric). Either can be membrane-associated. Both kinds have an ON state (usually GTP-bound) and an OFF state (usually GDP bound). GPCRs act as GEFs for specific G proteins. Signaling through G-Proteins 3 Monday, February 8, 2010 Signaling through G-Proteins Activated G-proteins then activate membrane-associated enzymes like adenylyl cyclase to become active and generate “ second messengers ” like cyclic AMP (cAMP). These small molecules then activate downstream enzymes in the cytosol, such as Protein Kinase A (PKA). Second messengers tend to be very small molecules that can diffuse rapidly throughout the cytosol. Note: some G-proteins are inhibitory, meaning that they shut OFF their targets when activated by a receptor. GPCRs act as GEFs for their associated G-proteins: they stimulate release of GDP and binding of GTP. 4
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DernburgLecture5_2-8-10_forprinting - Signaling through...

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