Alright. So here we're going to revisit our map of the lesson on bio signaling pathways, which we have down below. And of course, we know that we're exploring this map by exploring the left most branches first. And so we've already talked about G protein coupled receptors or G p C. R. S. And we've talked specifically about the stimulatory, a dental it cyclist. GPC are signaling pathway. And we've talked some details about the secondary messenger see amp and the enzyme PK in this pathway. And so now that we've explored this pathway here to its full extent, we're now going to shift over and talk about this pathway over here. And so this is going to be the inhibitory pathway for a dental it cycles GPC are signaling. So we're still talking about the same pathway except the inhibitory pathway, which is going to have some differences, uh, to it. And so let's go on and get started talking about this pathway. So here we're going to introduce inhibitory, a dental it cyclist. GPC are signaling which is not to be confused with what we covered in our previous lesson videos, which was stimulatory, not inhibitory a dental it cyclist GPC are signaling. And so what we need to recall from our previous lesson videos is that not all G proteins stimulate or activate the effect er enzyme. In fact, there are some G proteins that do the complete opposite and inhibit the effect er, enzyme. Now this inhibitory a dental it cycles GPC are signaling, has the same exact pathway as before. Except this time we have an inhibitory Alfa sub unit of the G protein or a G I that ultimately inhibits the activity of the effect er enzyme so that it creates less secondary messenger than before. And we'll be able to see this down below in our image now the integration of what we covered in our previous lesson videos, which was the stimulatory pathway and what we're talking about now, which is the inhibitory G PCR pathway. Thes two can be integrated together and can help to regulate the activity of the affect er, enzyme, so that the effect er enzyme is creating the exact amount, the appropriate amount of secondary messenger that the cell needs. And so if we take a look at our image down below at our example, image notice that we're showing you the activity of the effect er, enzyme a dental. It's cyclists being regulated by the inhibitory G PCR pathway. And so on the right side of our image Over here, notice we're showing you stimulation or the stimulatory pathway utilizing the stimulatory, G protein G s and on the right hand side of the image. Over here we're showing you the inhibitory g protein pathway or G I. And so on the left hand side, it's pretty much exactly what we talked about in our previous lesson video. So you can see epinephrine binds to the beta ADR energy GPC are causing a confirmation will shift that activates the G protein, causes it to swap out it's G d. P and replace it with G T. P. And then the Alfa sub unit of the G protein is going to disassociate and activate the ident lit cyclist defector enzyme so that it creates mawr. It converts more a teepee into secondary messenger See amp and so really nothing new over here on the left hand side of the image. Whereas if we take a look at the right hand side of the image, this is really the new part that we're introducing here. And so there's some inhibitory lie gone that we're not going to get into the details up that is going to bind to some inhibitory GPC are that is going to induce a confirmation. I'll shift in this inhibitory GPC are which is going toe activate an inhibitory g protein by promoting again the g d. P to be replaced with GTP just the same as it was over here. And so we have our dissociated g ir dissociated inhibitory G protein Alfa sub unit on the really only difference between this side over here and the stimulatory side is what we see right here and over here and so on the left hand side notice that the stimulatory pathway activates the dental it cyclists, whereas the inhibitory pathway over here is going to inhibit a dental it cyclist so that it converts less a teepee into see hamp. And so really, this inhibitory pathway over here is acting like the brakes in a car to help slow down the activity of a dental cyclists. And really, this stimulatory pathway over here is almost acting like the gas pedal of a car to help speed up the activity of a dental it cyclists. And so you can see how the gas pedal and the brakes can be used to regulate the speed or the activity of the dental it. Cyclist, defector, enzyme. And so, really, this year concludes our introduction to inhibitory, a dental it cycles. GPC are signaling, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our core. So I'll see you guys in our next video.
The addition of the nonhydrolyzable GTP-analog, GTPγS (shown below), is a common cell culture technique. If only affecting the inhibitory pathway, what effect would GTPγS have on cellular cAMP levels?
cAMP levels increase because adenylate cyclase can no longer hydrolyze GTP.
cAMP levels decrease because Gs remains in its inactive state and can no longer bind GDP.
cAMP levels decrease because Gi remains in its active state since it can no longer hydrolyze GTP.
cAMP levels increase because Gi remains in its inactive state since it can no longer hydrolyze GTP.
If a chemical is an inhibitor of the enzyme adenylyl cyclase, which of the following steps in the GPCR signaling pathway would be directly blocked?
Activation of gene transcription.
Exchange of GTP for GDP.
Ligand bound receptor activation.
Synthesis of the secondary messenger cAMP.
Inhibitory Adenylate Cyclase GPCR Signaling
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So here we're going to introduce yet another way to inhibit a dental it cyclist. GPC are signaling, and that is through GPC are desensitization. Now. When a signal is continuously present, creating repeated exposure, then cells need the ability to desensitized to that continuously present signal that's again creating repeated exposure. Now the process of desensitization is really defined as the dampening or the decreasing of the cellular response, even when the primary messenger or ligand still persists. And again that primary Lagan is continuously present, creating repeated exposure. Now desensitization is really understandable when you think about it in the context of you getting up in the early morning and walking into a room with really, really bright lights. Initially, your eyes air going to create a really strong cell response to those bright lights and your eyes air going to squint when you walk into that room with bright lights. However, over time, even when those bright lights still persist and those that bright light signal is continuously present, creating repeated exposure eventually over time, your eyes will desensitized to those bright lights, and so they will not create such a drastic cell response, and eventually your eyes will be able to open back up to the normal position that you have throughout the day. And so the desensitization of your eyes to bright lights is really similar to how GPC ours can also desensitize to, uh signals such as Liggins that air continuously present. And so really one of the major proteins that are involved in GPC are desensitization is the beta agin ergic GPC. Our kindness, which, as you can see by these bold ID letters right here, is commonly referred to as just the bark protein. And so the beta agin ergic GPC. Our kindness is indeed a kindness, so we know that it's going to fuss for late things and more specifically, it's going too fast for late. The beta agin ergic GPC are, which is the specific GPC are found in a dental it cyclist. GPC are signaling, and so the bark protein because again it is a kindness. It's going to fuss for late its substrate and again it's substrate is going to be C terminal, searing residues on the Ligon bound beta agin ergic GPC are and so why gang bound is really, really important here because again that is what's going to indicate that the signal is continuously present, creating repeated exposure. And so if we take a look down below at our image over here on the left hand side, notice that the very first step and GPC are desensitization Is that the lie gone that is continuously present? Creating repeated exposure uh, must actually bind to the beta agin ergic GPC are And of course, we can indicate that the epinephrine extra cellular lie again must bind to the beta Andrew allergic GPC are and again that is the very first step of GPC are desensitization. But then notice moving onto the second step over here in our second image, notice that the beta agin arctic GPC our kindness or bark is coming into play, which is this yellow protein that we see down below. And so again, because bark is a kindness, it's going too fast for late. The beta agin ergic GPC are, as we see here, the phosphor relation. And so in step number two down below, we can indicate that bark This kindness is going to again. Foss for Lee, the beta agin ergic GPC are now another major protein that's involved in GPC are desensitization is the protein beta arrest in which you can see by these bold letters. Right here is referred to as the bar protein, and so the Bader restaurant or the bar protein, is again a protein that's going to bind to the phosphor related GPC are essentially blocking or preventing the GPC ours interaction with the G protein and ultimately that's going to prevent the cell response from occurring and helped to desensitize. The GPC are from the signal and so this beta arrested or bar protein can actually initiate temporary endo site. Oh Sis of the GPC are and recall that Endo psychosis the E end here reminds us that it's going to allow toe enter the cell as a within a vesicles. And so this is going to make the GPC are temporarily inaccessible to the like and that is continuously present. And that also helps to desensitize. The GPC are from the continuously present like and and so if we take a look down below at our image here at our third step, notice that the beta arrest in protein or the bar protein is here in purple and it is binding to the fuss for related beta agin ergic GPC are and so beta arrest and binds to that foster related G PCR and essentially blocks it blocks its interaction with the G protein. So bad arrests and blocks the G protein association with the GPC are and it can also trigger temporary endo site Assis of the G p c R which we're not really showing here. But you can imagine this entire thing being brought down into the south Avea Endo psychosis removing it from the plasma membrane so that it will not again, uh, cause a cell response. Now notice Over here on the far right we have this little memory tool over here to help you guys remember the roles of the bark protein and the beta arrested protein in GPC are desensitization and so you can imagine that GPC are desensitization eyes only going to occur when the GPC are is kind of going rogue because there's so much signal that's present and the GPC are is just creating too much of a cell response. And so here what we have is the GPC are kind of going rogue here. He's just doing whatever he wants and he's robbing a bank here, as you can see And so when you have a G p c r, that's going rogue, you need a way to desensitize so that it does not, you know, cause any issues. And so what can happen is the beta adieu energy, GPC our kindness or bark here like this dog barking can essentially mark the rogue GPC are and that is going to essentially allow the officer beta arrested to come in and arrest the GPC are and prevent it from interacting with the G protein moneybag over here. So that way the GPC are is not going rogue and it's arrested temporarily until the signal kind of dampens down. But this here concludes our introduction to G PCR desensitization and we'll be able to get some practice with these concepts as we move forward in our course. So I'll see you guys in our next video
Inhibitory Adenylate Cyclase GPCR Signaling Example 1
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all right. So here we have a word problem as an example, and it says that a cell line expressing the beta adrianne ergic G PCR is incubated in epinephrine. For five minutes, the cells air, then Liszt or burst it open and the GPC are protein is purified to determine if beta arrested is bound to that purified GPC are the purified GPC. Our solution is examined by Western blot using an anybody against beta arrested. And that is really the data that we see in lanes number one and lanes number two down below and our image. And so taking a look at this image down below briefly notice that we have the direction of the gel migration. So the top of the gel is the starting place in the bottom of the jealous, the ending place on then notice that we have the exposure to epinephrine indicated down below in terms of the time. So zero minutes was in lane number one and five minutes was in Lane number two. Now notice that the problem goes on to say that the experiment was repeated but this time prior to and during epinephrine addition, the cells are incubated in an inhibitor that blocks beta adieu energy GPC our fast for relation by the GPC Our kindness bark And that is really the data that we see in lanes number three and lanes number four. And so notice that in lane number three in lane number four over here that we have the plus inhibitor on top of it, indicating that the inhibitor described here, uh, is utilized in lanes three and four. But it is not utilized in lanes one and two. And so it tells us that the results are shown down below and what conclusion can be made from the results or data And so notice that the expected beta rest inbound GPC Our band is right here in the middle. And so the Onley Lane that has this expected beta rest inbound GPC are banned is lane number to all of the other lanes. Do not have beta arrest inbound to the GPC are and so essentially what we need to do is take a look at the conditions in lane number two and what we can see is that exposure to epinephrine is important in order for beta arrested to bind, and so that is definitely an important feature because when there's zero minutes of exposure here in lane number one notice that there is no banned under the same exact conditions except with zero minutes of exposure and then notice that even if you do have exposure to epinephrine uh, if this inhibitor is present, then you will not have that band. You will not have beta resin bound to the GPC are. And so this band right here in Lane number two is telling us that in order for beta arrested to bind to the GPC are the receptor, the GPC are must be exposed and bound to It's like and And so that is really the main conclusion that we can make from this problem. So we could go ahead and indicate that a here is correct. Now, taking a look at option B, it says, in order for beta resting to bind the receptor cannot be exposed to its slide in. But of course, when we take a look at, uh, the receptor not being exposed to any epinephrine, zero minutes of exposure, uh, noticed that there is no band here. And so, of course, this is not gonna be the case because if bada resin bound when there was no exposure, then we would expect to see a band here. But that's not what we see. So be is incorrect. And of course, see is also incorrect because it says, in order for Beta arrested to bind, that bark must first be bound to the receptor. But of course, we know that bark does not bind to the receptor It on Lee fast for relates the receptor since it is a kindness and then of course, D is also incorrect because it says, in order for beta resting to bind, the inhibitor must first bind to the receptor. But of course, whenever the inhibitor is present noticed that the beta arrested protein is never bound to the GPC are which is why there are no bands here in lanes three and four. And so again, a Here is the correct answer to this example problem and that concludes this example. So I'll see you guys in our next video
How does GPCR termination differ from GPCR desensitization?
GPCR termination promotes GPCR signaling while GPCR desensitization overexpresses the GPCR.
GPCR desensitization involves degradation of the GPCR while GPCR termination promotes GTPase activity of Gα.
GPCR termination blocks the GTPase activity of Gα while GPCR desensitization promotes ligand binding.
GPCR termination resets the signaling pathway in the absence of ligand, whereas GPCR desensitization dampens the cell response even in the presence of ligand.
Which of the following statements about beta-arrestin and GPCRs is TRUE?
Beta-arrestin phosphorylates activated GPCRs.
Beta-arrestin can cause desensitization of a signal by inducing GPCR exocytosis.
Beta-arrestin is pre-bound to inactive GPCRs (no ligand bound).
Beta-arrestin binds to phosphorylated residues on the carboxy-terminus region of GPCRs.
Beta-arrestin binds to phosphorylated residues on the amino-terminus region of GPCRs.
Which of the following are involved in the desensitization of the β-adrenergic receptor?