Lipid-Linked Membrane Proteins

in this video, we're going to continue to talk more about lipid linked membrane proteins and so recall in our previous lesson videos, we already introduced lipid linked membrane proteins, and so we already know that these are lipoproteins because they're cove intently anchored or co valiantly attached to at least one lipid group within the by layer. And so, if we take a look at our image down below, notice that we're showing you to lipid linked membrane proteins. And so what you can see is that the protein portion is the tan ball that you see and notice that the protein is linked co violently to these lipid groups that are within the bi layer. And, of course, you could either have just one lipid group or you could have multiple lipid groups. Now, the lipid linked membrane proteins notice are on the periphery of the membrane, and so because the proteins themselves are on the periphery, technically, these are just a subcategory of peripheral membrane proteins. Now, what's interesting to note is that lipid link membrane proteins have a reversible association with the membrane, because really, all we need to do is cleave the co violent bond that's attaching the protein to the lipid portion, and then the protein would be released. And, of course, it would not be associated with the membrane anymore. And so not only is the lipid Link membrane protein association with the membrane reversible, but it's also a relatively weak association with the membrane, especially in comparison to integral membrane proteins. And so recall integral membrane proteins have a very strong or tight association with the membrane because they are embedded within the hydrophobic region, and they form lots and lots of hydrophobic interactions. However, here with lipid linked membrane proteins, these only have small, relatively small, uh, lipid groups that are embedded in the membrane. And so they're not nearly as tightly associate it as the integral membrane proteins. Now what's also important to note is that there are several different types of lipid linked membrane proteins, and some of the types are exclusively linked to just one side of the membrane. And so you might find depending on what type of lipid link protein it is, it may only be found on the intracellular side of the membrane and other lipid link proteins. Again, depending on the type, may Onley be found on the extra cellular side of the membrane and so moving forward in our course, we're going to talk about the four different types of lipid linked membrane proteins that you guys should know, and so I'll see you guys in that video.

in this video, we're going to introduce the four types of lipid linked membrane proteins, and so notice down below. We have this table right here that's giving you guys information on the four types of lipid linked membrane proteins, but also noticed that below the table we have this image that is also showing you the four types of lipid length membrane proteins. And so the numbers that you see up above in our table right here correspond with the numbers that you see down below in our image. And so moving forward, we're first going to fill out our table and then after our table is filled out, we'll go back down and revisit this image down below to discuss that. Alright, so that being said, the four lipid linked membrane proteins are palma toy, lated proteins, prin elated proteins, morass, dilated proteins and, like castle Phosphate Title in hospital or GP. I linked proteins for short, and so these four lipid linked membrane proteins differ from each other, based on the lipid group that their co violently attached to the co violent linkage that links the lipid group to the protein and the modifications that they have as well as by the side of the membrane that these lipid link membrane proteins are found on in terms of being found on the intracellular side of the membrane or on the extra cellular side of the membrane. Now the lipid link membrane proteins are actually named based on the specific lipid group that they are co violently attached to. For example, the palmetto related proteins, as the name implies, are specifically linked to the fatty acid pal mutate. The prin elated proteins, as the name implies with the preen, are linked to ISO preen, oId specifically far Nestle or Juran Ilja Randall groups, which will talk more about down below in our image once we get to it later in this video. And then, of course, the mere oscillated proteins, as the name implies, are specifically linked to the fatty acid mere state, and the Glide Castle phosphate title in a hospital or GP I linked proteins, as the name implies, are linked to the fatty acid phosphate title in a Seattle, which you might recall from our previous lesson Videos, is an example of a class of glycerol phosphor lipids. Now, in terms of the Covalin linkage that links the lipid group to the protein. Notice that both the palmetto related proteins and the prin elated proteins, which both start with the letter P contain thigh oh linkages and so recall that Theo linkages contained sulfur atoms and the Onley amino acid residue that contains a sulfur atom in its our group is, of course, the amino acid residue Sistine. And so they they're both, uh, contain Theo linkages with Sistine Residues in them. Now the palmetto related proteins specifically have a thigh. Oh, ether. I'm sorry, a Theo Esther link, whereas the prin related proteins specifically have a thigh oh, ether link, and we'll be able to distinguish between the Esther and the ether again down below in our image later when we get to it now, one thing that's important to note is that with the Palme toy lated proteins, the fi Oh Esther Link can form with any Sistine residue that's found in the protein. And so there's no requirement for the C terminal Sistine Residue or the End terminal Sistine Residue. It's any Sistine resident, and this is very different from the prin elated proteins, because the Theo ether link in pre related proteins formed specifically with the C terminal Sistine Residue and also with prion elated proteins. There is a modification that takes place, and this modification includes the methylation of the car boxful group or the C terminal end and recall. Methylation just means adding a CH three group. And again, we'll be able to visualize this in our image down below when we get to it. Now, in terms of the morass related proteins and the Glide Castle phosphate title in a Seattle or the GP, I linked proteins which note that neither of these start with letter P. Both of these have am I'd linkages and so we can put an am I here for both of them. Now, in terms of the merest elated proteins, they have an AM I'd linkage specifically with the n terminal glistening residue, whereas the GP I link proteins have an M. I linkage specifically with the C terminal, um, and and the C terminal am I Linkage is connected to the lipid group via a complex lipid anchor, which again will be able to visualize and our image down below now, in terms of the side of the membrane that each of these lipid link membrane proteins air found on notice that the first three palmetto related preen, elated and mere oscillated proteins are all found on the intra cellular side of the membrane. And so weaken right interest cellular side here. And so these three here are almost exclusively found on the intracellular side of the membrane, whereas the very last won the GP I linked one is almost exclusively found on the extra cellular side of the membrane on the outside of the cell. And so now that we've completed our, uh, table up above, we can now take a look at our image down below. And so as a reminder, the numbers that we see in our table correspond with numbers that we see down below in our image. And so the number one here corresponds with the Palme toy lated proteins. And of course, as the name implies, palmetto related proteins are co violently linked to the fatty acid pal mutate and noticed that the protein that we have here, highlighted in yellow, has an amino end and a car box a lend and the protein is specifically linked to the pal mutate fatty acid via a thigh Oh, Esther linkage, as we have highlighted here in blue and notice that the Theo part is referring to the sulfur atom and the Onley amino acid residue that contains a sulfur atom in its our group is the amino acid Sistine. And so notice that this Sistine is appearing really at any Sistine residue within the protein. It's not specifically the seed, the internal Sistine or the C terminal Sistine. It's really any internal Sistine residue within the protein. And, of course, this is a thigh. Oh, Esther linkage here because recalled that Esther's are going to have a carbonnel group like this linked to the sulfur atom. And so this is exactly the thigh Oh, Esther that we were referring to up above in our table. And so if we go back up to revisit our table here, notice that this is exactly what we were saying. Palmetto related proteins have a thigh Oh, Esther linkage with any Sistine residue, Not necessarily the end terminal or C terminal Sistine residue any Sistine residue, and they're specifically linked to the fatty acid pal imitate and also noticed that there specifically found on the intracellular side of the membrane and so looking down here, notice the intracellular side is down here, whereas the extra cellular side is up here. And so the first three of as we mentioned are found on the intracellular side, whereas the last one is found on the extra cellular side. Now the number two that we have here is going to correspond with the preen, elated protein. And of course, the preen indicates that it's gonna be, uh, containing is a pre noise such as either far Nestle or Juran Ilja Randall who structures were showing you here. And these are really just the two most common ice opera noise that air linked and pre related proteins. And so notice that the protein here has its amino group over here. And so it's car boxing group is over here and it's car boxing group is actually involved with the linkage to the ice opera annoyed. And so this means that the sulfur atom here is going to be part of the C terminal Sistine residue specifically, and notice that the sulfur is not forming an Esther because there's no Carbonnel group. Instead, the sulfur here is a thigh oh, ether linkage and recall that ethers look like this with two are groups on either side. So this is the ether. Whereas this over here is the Esther, so you can compare them side by side. And so also noticed that this C terminal end has a modification to it because it is being methylated. And so we have a car boxful methyl group over here. And so again, this is exactly what we said up above in our table. And so if we revisit it briefly noticed that the prin related proteins are specifically linked to is a paranoid such as far ness Orgeron adrenal. And they contain a Theo ether link specifically to the C terminal Sistine Residue. And also the C terminal and the car box will end is gonna have a modification with a methylation group, a ch three group attached, as we indicated down below, Right here. Now moving on the third one here is, of course, going to be the Mir. Mir ist elated protein, and so we could go ahead and put that here. And of course, the as the name implies, the merest related protein is going to be linked to the fatty acid mirror state as we see, But notice that the two previous ones palmetto related and pre emulated both started with peas and both contained thigh Oh, languages. Whereas, uh, murals delayed. It does not contain a piece. So it's not gonna contain a thigh a linkage. Instead, it's gonna contain an AM I'd language as we see right here. Um, right here this is an AM I'd linkage with the nitrogen atom and the Carbonnel group and noticed this time that the protein has its C terminal and over here not involved with the linkage. And instead, it's the end terminal end here that is involved with linkage to the fatty acid mirror state and notice specifically that the our group of this amino acid is a hydrogen atom, which means that this is specifically a glistening amino acid residue. Here a the end terminal end because of this hydrogen atom as our group. And so this is exactly what we mentioned up above in our table. Notice that the miras dilated proteins here are specifically linked to the fatty acid mayor state and they have an AM I'd linkage specifically with the n terminal glisten residue and again there also found on the intracellular side of the membrane along with the prin elated and palmetto related proteins. Now, last but not least, we have number four here, which is gonna be our GP I linked protein. And of course, the GP I linked protein, we said specifically are linked to a phosphate title in a Seattle group which we have right here and recall Foster title in Hostile Group is just a glycerol fossa lipid, one of the glycerol foster lipids that we have highlighted right here. And of course, we also mentioned that, uh, it's going to be The protein which is noticed up above right here is going to be linked via its C terminal link. It's gonna be linked Viet C terminal specifically by an AM, I'd linkage. And so here we have another AM I'd linkage linking the C terminal end to the fatty acid down here. And so notice that in between here we have this complex linkage that we were referring to previously this complex lipid anchor. And so really, we're not gonna get into the details of this complex lipid anchor here, But you can see that it does have a tetra sack ride and it And it also has this phosphor ethanol amine group that you can see right here and specifically the GP I linked proteins are found on the extra cellular side of the membrane, and so that's also important to note. And so this here concludes, our introduction to the four types of lipid linked membrane proteins and moving forward will be able to get some practice applying the concepts that we've learned. And so I would recommend filling out this table a few times and closely comparing the table up above with the image down below to solidify these learning objectives. And so I'll see you guys in our next video.

Prenylated proteins: 

a) Are integral membrane proteins. 

b) Contain amide linkages to straight-chain fatty acids. 

c) Contain ester linkages to straight-chain fatty acids. 

d) Are post-translationally modified proteins. 

e) None of the above.

• A. Are integral membrane proteins.
• B. Contain amide linkages to straight-chain fatty acids.
• C. Contain ester linkages to straight-chain fatty acids.
• D. Are post-translationally modified proteins.
• E. None of the above.

Which of the following lipid-linked proteins are located primarily on the exterior surface of the membrane? 

a) Prenylated proteins.

b) Myristoylated proteins.

c) Plamitoylated proteins.

d) GPI-linked proteins. 

e) Farnesyl-linked proteins.

• A. Prenylated proteins.
• B. Myristoylated proteins.
• C. Plamitoylated proteins.
• D. GPI-linked proteins.
• E. Farnesyl-linked proteins.

Which of the lipid anchor modification(s) is (are) readily reversible with the help of thioesterases? 

a) Myristoylation. 

b) Palmitoylation. 

c) Glycosyl-phosphatidylinositolation (GPI). 

d) All of the above. 

e) None of the above.

• A. Myristoylation.
• B. Palmitoylation.
• C. Glycosyl-phosphatidylinositolation (GPI).
• D. All of the above.
• E. None of the above.