Upon activation by a receptor, a G protein exchanges bound GDP for GTP, rather than phosphorylating GDP that is already bound. Similarly, the a subunit-GTP complex has a slow GTPase activity that hydrolyzes bound GTP, rather than exchanging it for GDP. Describe experimental evidence that would be consistent with these conclusions.
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- What is meant by intrinsic GTPase activity? Exchange of GDP for GTP on the a-subunit of the G protein Inhibition of GBCR receptor activity Activation of Adenylyl Cyclades Breakdown of cAMP by phosphodiesterase Spontaneous hydrolysis of GTP on the a-subunit of the G-proteinCompare and contrast GPCR and RTK signaling. What role does GTP play in each? What role does phosphorylation play? How do these two signaling types compare to steroid signaling with respect to gene activation?Compare and contrast GPCR and RTK signaling. What role does GTP play in each? What role does phosphorylation play? How is each signal differently amplified? How do these two signaling types compare to steroid signaling with respect to gene activation?
- Signal-transducing heterotrimeric G proteins consist of three subunits designated α, β, and γ. The Gα subunit is a GTPase switch protein that cycles between active and inactive states depending on whether it is bound to GTP or to GDP. Review the steps for ligand-induced activation of effector proteins mediated by the heterotrimeric G proteins. Suppose that you have isolated a mutant Gα subunit that has an increased GTPase activity. What effect would this mutation have on the G protein and the effector protein?When adrenaline (epinephrine) binds to adrenergic receptors on the surface of a muscle cell, it activates a G protein, initiating a signaling pathway that results in the breakdown of muscle glycogen. How would you expect glycogen breakdown to be affected if muscle cells were injected with a nonhydrolyzable analog of GTP, that can’t be converted to GDP? Consider what would happen in the absence of adrenaline and after a brief exposure to it.Why is the GTPase activity of G proteins crucial to the proper functioning of a cell? Propose a theory as to why G proteins have not evolved to catalyze GTP hydrolysis more efficiently.
- If you have a protein kinase that is regulated by both small molecule inhibitors as well as by phosphorylation, and is part of a cooperative enzyme complex that works as part of a larger pathway involving kinase and GTPase proteins please explain where on this protein regulation could occur, how different types of inhibition could control the function of the protein as well as the function of the complex, and how the protein could regulate other proteins. (This question was previously answered but it was answered incompletely mentioning an herbicide developed in the 1950's. Apparently, it was a plagiarized excerpt from an NCBI article. This is a repost for a full and complete answer. Thank you so much for your help! :) )Continuous exposure of a Gαs protein coupled receptor to its ligand leads to a phenomenon known as desensitization. Describe several molecular mechanisms for receptor desensitization. How can a receptor be reset to its original sensitized state? What effect would a mutant receptor lacking serine or threonine phosphorylation sites have on a cell?You decide to investigate cell signaling of a pair of newly identified GPCRs, GPCR-W and GPCR-Z. Each binds the same ligand, but activates different downstream heterotrimeric G-proteins that act on adenylyl cyclase. You discover that ligand binding has opposite effects on adenylyl cyclase activity for each receptor. GPCR-W causes an increase in adenylyl cyclase activity, while GPCR-Z causes a decrease in adenylyl cyclase activity. You obtain a cell line expressing GPCR-W, GPCR-Z, the relevant G-proteins, and adenylyl cyclase. There is baseline adenylyl cyclase activity producing a baseline amount of cAMP. You embark on a research project to characterize the following mutations in the components of the signaling pathway. 2. Will each of the following mutations increase or decrease the levels of cAMP inside the cell upon adding the ligand to the cell culture? A mutation in GPCR-W that prevents G-protein activation? A mutation in GPCR-Z that prevents G-protein activation? A mutation in…
- You decide to investigate cell signaling of a pair of newly identified GPCRs, GPCR-W and GPCR-Z. Each binds the same ligand, but activates different downstream heterotrimeric G-proteins that act on adenylyl cyclase. You discover that ligand binding has opposite effects on adenylyl cyclase activity for each receptor. GPCR-W causes an increase in adenylyl cyclase activity, while GPCR-Z causes a decrease in adenylyl cyclase activity. You obtain a cell line expressing GPCR-W, GPCR-Z, the relevant G-proteins, and adenylyl cyclase. There is baseline adenylyl cyclase activity producing a baseline amount of cAMP. You embark on a research project to characterize the following mutations in the components of the signaling pathway. 2. Will each of the following mutations increase or decrease the levels of cAMP inside the cell upon adding the ligand to the cell culture? A mutation in Gi that prevents release of bound GDP. A mutation in Gs that prevents GTP hydrolysis. A mutation in Gi that…Does adenylate cyclase become more active when the inhibitory (Gia) protein is mutated and increases its intrinsic GTPase activity?Briefly describe the following properties of the Rab and Arf GTPases: a) Size, structure and cellular localization (for structure I want to know if they are lipidated and any other unique features) , b) How are they activated and inactivated (i.e. include the GEFs and GAPs), c). Give an example of downstream cellular effects.