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10 Cards in this Set
- Front
- Back
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What is a GPCR?
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G-Protein Coupled Receptor. It is a 7-transmembrane domain protein receptor that binds an extracellular ligand and interacts intracellularly with a G-protein.
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What generally occurrs to the G-protein subunits once the GPCR binds its receptor?
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A NEF (nucleotide exchange factor) converts alpha-GDP (inactive) to alpha-GTP (active). Alpha and Beta-Gamma subunits separate. Both "a" & "By" subunits interact with effector proteins located on the intracellular side of the PM.
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How is a G-protein inactivated?
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RGS (a GAP or GTPase activating protein) increases the intrinsic GTPase activity of the alpha subunit by 2000 fold. Alpha-GTP is converted to alpha-GDP, which induces reassociation with the By subunit.
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How is a GPCR inactivated?
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Two mechanisms can inactivate a GPCR.
1. Heterologous: PKA/PKC phosphorylates the receptor, so that it cannot bind the G-protein, and therefore has less affinity for its ligand. This can occur to both ligand-bound or not-bound GPCRs. 2. Heterologous: active By subunit recruits GRK's (GPCR kinases) that phosphorylate ONLY ligand-bound GPCRs. *in both these mechanisms, once GPCR is phosphorylated, it recruits and binds to arrestin. The complex either is taken into the cell and degraded, or dephosphorylated and recycled. |
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What are the four major types of alpha subunit families?
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1. alpha-s: activates adenylyl cyclase
2. alpha-i: inhibits AC 3. alpha-q: activates phospholipase C 4. alpha-12/13: activates small G proteins |
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T/F: different ligands can bind the same G-protein coupled receptor.
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True, although they may bind with different affinities.
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Beta-adrenergic receptors are an example of GPCR's. They bind norepinephrine and epinephrine. What types of responses are seen in patients w/ increased levels of Epi or Nori-Epi?
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"Fight or Flight" is activated: increased cardiac output, gluconeogenesis, glycogenolysis, blood pressure, skeletal muscle dilation.
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Beta blockers are often used to treat high blood pressure and other related conditions. How do they do this?
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Beta blockers can inhibit the binding of nori-epi or epi to their receptors, thereby lowering blood pressure, heart rate, etc.
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How does the cholera toxin work?
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It ADP ribosylates the alpha-s subunit of the G protein, preventing it from hydrolyzing GTP. Therefore, it is always active, leading to activation of cAMP, PKA, and CFTR. NaCl and water are over secreted into the lumen. THis results in severe diahrrea and dehydration.
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How does the pertusis toxin work?
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It ADP ribosylates the alpha-i subunit, preventing it from inhibiting AC. The cAMP signal is always on.
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