as an amino group is connected to the fatty acid to make second tail with first tail is made of the structure of sphingosine itself that has a long hydrocarbon chain are mostly present in lipid rafts. If you remember, we talked about them in the summer when we were talking about lipids. So they make lipid rafts, patches within the membranes in which sphingolipids are highly concentrated. in addition to some other glycoproteins, cholesterol, etc., and they are responsible for performing certain functions.
Sphingomyelin, specifically, as the name implies, it has also a phosphate group and choline. Phosphate and choline. And it is a major component of the myelin sheath.
That's why it's called sphingomyelin. And by glycolopids, they have sugars in their head groups. It can be just a monosaccharide, like glucose or galactose.
It can be disaccharide, oligosaccharide, etc. Making different types of glycolipids, from cerebrosides, globosides, gangliosides, etc. And we'll go through these one more time again, inshallah.
How do we synthesize sphingomyelin? Sphingomyelin is a known structure. As we said, there's sphingosine. We have choline in the head group. and phosphate in addition to a fatty acid that makes the second tin.
We start the synthetic pathway by making sphingosine. I start with palmitic acid that has to be activated by adding a CoA. So it becomes palmitoyl CoA.
The palmitoyl CoA I will react it with serine. Serine amino acid in a condensation reaction. What happened in this reaction?
Actually, we lost this part. We condensated, we added the palmitoyl-CoA to the serine. We lost the CoA.
Sorry, we lost the CoA. It came out. We lost a carboxyl group. Where did the carboxyl come from? From the serine.
We lost it also. And, sorry for you. reduction in this reaction because we lost oxygen and this is associated with the oxidation of NADPH to NADP+.
Remember, it is a biosynthetic pathway. So it is possible that I am doing a reduction to the coenzyme, not oxidation, like degradation. So I have a long R chain or long hydrocarbon chain that came from palmitoyl.
or palmitic acid so if you in the aminogrup here the serine and the OHs as well Sfinganine will react with a fatty acid group. We're going to use it in the active form. in which the fatty acid is connected to a coa and in every place we used fatty acids in the synthetic or even degradative pathway we had to activate it by adding a coa will be used for isolation of sphingonine a sedation of sphinganine in one aspect the other point the other change is going to be the desaturation why because remember that the palmitic acid is saturated it is a saturated fat acid but sphingosine has a double bond if you have a double bond next to the at the beginning of the hydrocarbon chain that makes one of the tails so this reaction involves both acylation to add the fatty acid and desaturation to introduce the double bond So this would make sphingosine.
This is the R chain already there and this is the fatty acid that was added by an ester bond, sorry by an amide bond to the amino group of sphingosine. This structure here. and this is the double bond This is the double bond that was introduced during the reaction. This structure here where we have a fatty acid connected to the amino group and sphingosine structure, all of this structure is considered as ceramide.
Sphingosine plus fatty acid equals ceramide. The ceramide, if you remember, is the parent molecule of all sphingolipids, whether it is sphingomyelin or... glycerol glycerol so it's a very important ingredient for glycerol glycerol is a very important ingredient for it will be released as di-asin glycerol, and I take the phosphocholine and add it to the first carbon of sphingosine to make sphingomyelin.
Notice, during this synthetic pathway, we needed different coenzymes. The first one is NADPH. It is a biosynthetic pathway, and it was needed in the first condensation reaction between palmitoyl-CoA and serine. We also needed to add a second coenzyme to the first condensation reaction.
needed in the PLP nation PLP period of cell phosphate which type of enzymes need this type of coenzymes PLP Plp, it needs PLP, p-phosphate and NADPH. We also needed FAD during the desaturation. We oxidized the sphingine and reduced FAD to FADH2.
time isn't this these are the synthetic steps for sphingomyelin notice that we used amino acids to make lipids we used amino acids to make lipids just keep this in your mind one of the molecules that can be made of amino acids is the whole screen combined with our sphingolipids but how do we degrade sphingomyelin and what are the enzymes important in this degradative process responsible for degradation of sphingomyelin specifically is called sphingomyelinase. Sphingomyelinase. What does it do? It's going to remove the head group, the phosphate and choline, or phosphoryl choline.
The leftover of the structure is ceramide. How can we degrade ceramide by an enzyme ceramidase? Ceramidase removes the fatty acid and leaves the rest of the structure, the sphingomyelin.
Since the sphingomyelinase removes the headache group, including the phosphate group, then it can be classified as phospholipase C, which is one type of phospholipase C. Remember last time we discussed how phospholipase C does the degradation. It's going to remove the phosphate group for glycerophospholipids plus the headache group. So phospholipase C, as I said, is going to cleave the phosphate. with the head blue, and sphingomyelinase is going to do the same.
It's going to remove the phosphate and choline, or phosphorylcholine, so it is a type of phospholipase C. The sphingomyelinase enzyme is a lysosomal enzyme, so if it is deficient due to genetic mutation, so this results in this disease, Neiman-Pick disease. Neiman-Pick disease. So the sphingomyelinase is going to accumulate.
the lysosomes since this enzyme is found in the lysosome so the sphingomyelin enters into the lysosome for degradation but it doesn't get degraded so what we see here is this accumulation of sphingomyelin within the cells specifically within the lysosomes of the cells this lysosomal disease and it's considered as a lysosomal storage disease because the sphingomyelin is going to be stored within the lysosomes and because it's not degraded It has multiple types based on the severity of the disease, type A and B. Type A is more severe than type B, and it is more common in, again, Jews, Specifically Ashkenazis, they are from the European countries. Now we come to the other type of sphingolipids, which are glycosphingolipids or glycolipids.
Glycolipids, if you remember, they again have ceramide as a parent molecule in their structure, and they are also called glycolipids. both fatty acid attached to the amino group and the other tail made of sphingosine itself but then we have a sugar attached through carbon number two through the OH group that's why it is an all glycosidic bond And carbon number two has an OH, and this oxygen will connect the ceramide to the sugar through the oxygen. That's why it is an O glycosidic linkage.
Glycolipids are important in cellular adhesion. They're important in cell-cell interaction and communication. They're important for recognizing cells and immune system functions, as well as in signaling pathways. That's why we expect them to be more concentrated in the outer layer. leaflet of the plasma membrane.
They might be very large in their head group because the sugar can be oligosaccharide, it can be disaccharide, or even monosaccharide. And the largest definitely is the oligosaccharide. Glycolipids can be classified based on the size of their sugar component, and if it is single or monosaccharide.
They're considered as cerebrosides, gluco or galactoserebrosides. Gluco has glucose and galacto has galactose attached as a heavy group of glycolipid. These are considered neutral because the heavy group is just the sugar itself. There are no modifications like acetyl-A-10 or sulfation or whatever, any other changes.
If we have more than one sugar, two or more, di-saccharide or oligosaccharide, attached to the ceramide, then we would have globoside. In globoside, still, we don't have modified sugars. That's why they're considered as neutral glycosphingolipids. We do modifications with charges.
The other category of glycosphingolipids is the acidic ones. Acidic ones because they have a negative charge. And this negative charge can be introduced to presence of carbon. with the presence of sulfate group in the modified sugars.
So we have modified sugars in the chain of these, the sugars attached to the sphingolipids. An example of these glycosphagolipids is gangliosides. And gangliosides are attached to oligosaccharides, which die, oligo, they have to be three or more sugars.
And they have to include at least one or two sugars. One, sialic acid. I will say me-na-na, one of so. And acetanuramic acid. It is the same as sialic acid.
So, we can distinguish globocytes that have oligosaccharides versus gangliosides that are attached definitely to oligosaccharides by having sialic acid. Sialic acid is present in gangliosides, but not in globocytes. So, we have these modified sugars by adding sulfate or... amino group or even in oxidation to carboxyl group. How do we synthesize the glycosphingol lipids and the modified ones with sulfates in their sugar structure?
The synthesis of these glycol lipids... in the Golgi apparatus, not in the smooth endoplasmic reticulum as it is usually for other types of lipids. And the ceramide will be used as a parent molecule. we made ceramide, we're going to add the sugar component, just like sphingomyelin.
We synthesized the ceramide, meaning palmitoyl-CoA, as well as serine, and then we added the fatty acid, so now we have ceramide. For sphingomyelin, we added phosphorylcholine that came from glycerophosphonates. Here we're going to add sugar, whether it is just monosaccharide, disaccharide, or polysaccharide.
So we can add the first one, so for example... of a test of galactose, by galactosell transferase, galactosell transferase to make galactosell ceramide, or galactosellabroside, galactosellabroside. If I'm going to modify this one, we can use... Sulfotransferase enzyme that's going to use PAPs as a donor of the sulfate group.
The first step I just added sugar as it is. as galactose by a galactosal transferase. But then suppose I'm going to modify it for the synthesis of other types of glycosphingolipids, for example, by sulfation. So the enzyme is going to be cellful transferase. I need a sulfate donor.
The sulfate donor is going to be PAPS, which is phosphoadenosine phosphosulfate. Phosphoadenosine phosphosulfate. So that is it.
That's the structure. PAPS is considered as a donor of the sulfate group or carrier of the sulfate group. So we add it to the galactose, so it becomes sulfogalactosylceramide. Sulfatide.
It's considered as a sulfatide. To sum up all the synthetic pathway for different types of glycolipids and sulfatides, so we start with ceramide, as we said, palmitoyl-CoA plus serine, that is sphinganine, sphinganine we add to it, fatty acid so we would have ceramide once we have ceramide we may add phosphocholine from glycerophospholipid and homophosphatidylcholine that becomes diacetylglycerol and we can produce the first type of sphingyl little bit you know a single mile type we can add also galactose like this example here to ceramide and it has to be carried by UDP UDP galactose then we release UDP and add characters to produce galactose here beside if you want to make sulfur ties then we need perhaps and a cell for transferase to add this more of course to modify the sugar component in this cerebral side and to make sulfur time If we would like to make a cerebroside, another simple cerebroside, a glucocerebroside, we can add UDP glucose, we release UDP, and make a glucocerebroside. For more complex ones, like globosides and gangliosides, we are going to add them sequentially, one by one.
And all these sugars have to be carried by UDP again, just like... So we add multiple sugars, two, three, four, et cetera, until we make globocytes, provided we don't have any sialic acid in globocytes. Then we can add sialic acid, which is nano, and this nano will be carried by CMP. CMP will be released, and nano can be added to globocytes to make ganglion side. ...degrade these sugar-containing sphingolipids or glycolipids.
Remember, they are present in plasma membrane. They are in the outer leaflet of the membrane, so they are... exposed to the outside environment of the cell.
The first step is their internalization into the cell and phagocytosis. They're already part of the membrane, so invagination of the membrane to the inside. like this to make this physical that can punch off the membrane and go to the inside of the cytosol of the cell then the physical is going to fuse with the early in the soul that becomes after some changes late in the song by the late in the song is going to fuse with the lysosome and remember my song contains multiple digestive enzymes that are going to remove these sugars first before it's going to degrade sphingolipids themselves or the structure, the basic structure. It's going to degrade the head group.
And the head group in this case contains different sugars. And the removal of these sugars, this is the ceramide, the parent molecule, and this is the sugar component in these glycolipids. So the removal will start from the furthest sugar. And it'll go on.
but then I go closer to the ceramide. So we remove them sequentially by different enzymes based on the type of sugar that's present in the oligosaccharide. For example, if I'm going to cleave this galactose, I need a beta-galactosidase that is present in the lysosome. Then for the N-acetylgalactosamine, We need hexose aminidase. Hexose aminidase, it will remove the hexose that has an amino group in acetylgalactose, in this example, or in acetylglucose, for example.
There's also another... enzyme specific for the Nana to cut say acid or Nana is more in your amenities or say any days not so many days or say any days that's going to cut leave the structure of ganglion sites. Then we would have ceramide, ceramides. We already have ceramides that can degrade ceramide and remove the fatty acid from sphingosine.
Let's have some applications on diseases related to the metabolism and degradation of sphingolipids. And they are mostly lysosomal diseases, related to the enzymes, lysosomal enzymes involved in the degradation. pathways for sphingolipids. So this means that the degradation of these specific types of sphingolipids will be compromised.
Then they will accumulate in the lysosomes, resulting in large lysosomes within the sphingolipids. these cells, depending on the deficient enzyme in this case. They are very valuable in terms of signs and symptoms, in terms of severity, in terms of their distribution and prevalence. There might be some mutations in the same gene, different mutations within the same gene, or there might be different genes that can be defective or affected by mutations resulting in a certain disease.
They have allele heterogeneity and locus heterogeneity, depending whether it is multiple gene mutation or multiple mutations within the same gene. Most of the time, these mutations are autosomal recessive. The patients have to have two mutations in the two genes for the phenotype to appear, to be affected by the disease. But we'll see what just one example. example that is excellent.
They're relatively rare diseases, but again, they are more common in Ashkenazi Jews. The first disease is called Ty Sachs disease. Ty Sachs disease, the problem is in hexoaminidase, mutation in hexoaminidase.
What does it do? which type of sugar does it believe in a still galactosamine or in a still modified sugars with an amino group for the master glucosamine and a still galactosamine this is a disease that will accumulate this type of sugars, we're going to call them GM2. What does GM2 mean? In this type of phospholipids.
Based on the number of sugars present in the structure of... sphingolipids we can classify them in by different gm classification gm1 gm2 gm3 etc so for example look at this example here so this is the ceramide failing glucose galactose and acetyl galactosamine and then we have four this is considered as gm2 and at the maximum we can have is five sugars What is the number that I should subtract out of 5 to get 2? 3, the number of other sugars in the structure 5 minus how many sugars I have in the structure of the glycolipid other than Nana So we have the classification Here 5 minus 3, we have GM2 3 other than Nana, here 4 For example, this leg, GM1 Here 1, 2, 3 So this is one, sorry, yes.
How many sugars do I need to decrease? One, two, three, four. Four sugars other than Nana. Five minus four, GM1.
Five minus four, GM1. Okay, GM3, one, two. So the more you increase the number of GM, it has less sugars attached to the sphingolipid. in glycolipid specifically.
This type, the whole GM2, would specifically accumulate in the lysosomes of these patients, and this results in destruction in different places, specifically in the nervous system, neurodegeneration that may result in seizures, you see blindness, then you have also muscle weakness, etc. Again, the deficiency is the most important. thing to get out of this is Hixomelidase A deficiency, that is a lysosomal enzyme, then it is a lysosomal storage disease that would accumulate.
The size and shape of the lysosomes is much larger than that in a normal patient, within neurons specifically. The second disease is Goucher disease, and this is considered as the most common disease of lysosomal storage diseases. And the deficiency in this case is in glucosidase.
What does it do? It's going to the great glucocerebrosites. It removes glucose from the ceramide.
So we know that ceramide is glucose. In this case, there would be accumulation of what? Glucocerebrosites.
There is no GMO or anything else. These are not glucosides. The most used treatment so far for this disease, because it is more common and you expect to have more patients, is glycogen. which is enzyme replacement. They can replace this glucosidase enzyme, but it is very costly.
It is very expensive. But it is possible. Ignore about this, and this is another disease, which is metachromatic decodystrophy, which is the accumulation of sulfatides, because it has a relationship with the enzyme involved in the metabolism of sulfatides, which is the aryl sulfatase, that removes the sulfate group out of the sugars.
So it's metachromatic decodystrophy. Another disease is Faber disease, the only X-linked. Sorry, not Faber, Fabry. Fabry disease is the only X-linked. Faber disease, in this disease...
in enzymatic deficiency is in ceramides. Ceramides is responsible for removing the fatty acid from ceramide to produce fatty acid and sphingosine. In this disease, there will be accumulation of... ceramide and this results in problems in the joints of these some distortions there are deformities in the joints there would be also painful deformities in the joints painful joints so it appears in this way not in the normal way like the gaps here in the hand between them as in the image of the skin this is the result They also have other signs and symptoms other than the problems in the joints and deformities in the joints.
They have a horse cry. They also have some tissue granulomas and other problems as well in Farber disease. The most common one in these disosomal stories.
diseases. How do we diagnose people or patients affected by these different lysosomal storage diseases that are related to sphingolipid metabolism and degradation? I have two ways. I can do a DNA analysis of the gene or suspected gene. I do sequencing and I compare its sequence to the normal sequence so I can tell what whether there is a mutation and whether this mutation is going to have an effect on the produced enzyme or results in deficiency of the enzyme.
The other thing is to measure the enzymatic activity of the enzymes in these patients after culturing some cells from it. So I take a biopsy from them and I culture cells. And the easiest cells to culture are the fibroblasts, or even peripheral leukocytes from the blood sample. So I culture the fibroblasts.
them and measure the enzymatic activity. It's a biochemical test. Either a biochemical test or by analyzing a DNA molecular test.
After diagnosing these patients, there are available treatments. Just enzyme therapy treatment, sorry, enzyme replacement treatments such as that used in gouture disease and febrile disease. But it is very expensive.
And there is also another option by bone marrow transplantation. There is also another strategy for treating these patients. For example, I can reduce the synthesis of certain types of these.
by using different medications, by a pharmacological compound. I can affect or inhibit the synthesis of these types. So its synthesis is just limited for the use of the cells.
and there is no more of these molecules produced to be directed for degradation. It reduces the amount of degradation, so it reduces the problems that are associated with it. Okay. Fabry disease, as we mentioned, is the only one that is X-linked.
We didn't mention much details, but it is related, its deficiency is related to a mutation or mutation in galactosidase, not glucosidase, like gout. Okay. galactosidase, there would be accumulation of galactocerebroside in Fabry disease, resulting in different problems in the heart, in the kidney, etc.
Does anyone have questions on metabolism of sphenovolipids, whether it is synthesis or degradation? Why did you put the image of Abul-Hol in the first place? What is his relationship with the subject? What is the relationship? What does Sphinx mean?
What is the similarity between them? Mysterious. Like, in the whole, it's mysterious. No one knows why it looks like that.
The human head is a lion's body. And the same thing with the lipids. There are so many unknown information of...
sphingolipids. It's not possible from the point of view of the synthesis and degradation as far as the function is concerned. As you remember, in the summer when we discussed their structure, we mentioned that they are mostly present or they're present in high concentration in lipid rafts.
And lipid rafts, until now, There are some research results that show their involvement and importance in facilitating HIV infections, facilitating other viral infections as well. For example, prion diseases, they are concentrated in patches, they are very small, they are very close to each other, so they facilitate these changes. As the prion said, it changes the adjacent protein. the normally folded protein in the affected patient, it becomes old.
It's called a proteinaceous infectious particle. It becomes old and changes its structure into the misfolded protein. So still their normal function under normal conditions is not really well understood.
That's why they are mysterious. And I'm telling someone sphingolipids in relation to sphinx. Okay. Does anyone have any questions? No?
Okay. I'll give you the permission. Thank you.