Cerebroside
Encyclopedia
Cerebrosides is the common name for a group of glycosphingolipids called monoglycosylceramides which are important components in animal muscle
and nerve
cell membrane
s.
They consist of a ceramide
with a single sugar residue at the 1-hydroxyl moiety. The sugar residue can be either glucose
or galactose
; the two major types are therefore called glucocerebroside
s and galactocerebroside
s. Galactocerebrosides are typically found in neural tissue, while glucocerebrosides are found in other tissues.
Galactosylceramide is the principal glycosphingolipid in brain tissue. Galactosylceramides are present in all nervous tissues, and can compose up to 2% dry weight of grey matter and 12% of white matter. They are major constituents of oligodendrocytes. Glucosylceramide is found at low levels in animal cells such as the spleen, erythrocytes, and nervous tissues, especially neurons. Glucosylceramide is a major constituent of skin lipids, where it is essential for lamellar body formation in the stratum corneum and to maintain the water permeability barrier of the skin. Glucosylceramide is the only glycosphingolipid common to plants, fungi and animals. It is usually considered to be the principal glycosphingolipid in plants. It is a major component of the outer layer of the plasma membrane. Galactosylceramides have not been found in plants.
Monogalactosylceramide is the largest single component of the myelin sheath of nerves.The sugar moiety is linked glycosidically to the C-1 hydroxyl group of ceramide, such as in lactosylceramide. Cerebrosides containing a sulfuric Ester (sulfate) group, known as sulfatides, also occur in the myelin sheath of nerves. These compounds are preferably named as sulfates of the parent glycosphingolipid.
..The corresponding defect for galactocerebrosides is Krabbe disease
.
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
and nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s.
They consist of a ceramide
Ceramide
Ceramides are a family of lipid molecules. A ceramide is composed of sphingosine and a fatty acid. Ceramides are found in high concentrations within the cell membrane of cells. They are one of the component lipids that make up sphingomyelin, one of the major lipids in the lipid bilayer...
with a single sugar residue at the 1-hydroxyl moiety. The sugar residue can be either glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
or galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
; the two major types are therefore called glucocerebroside
Glucocerebroside
Glucocerebroside is any of the cerebrosides in which the monosaccharide head group is glucose.-Clinical significance:...
s and galactocerebroside
Galactocerebroside
A galactocerebroside is a type of cerebroside consisting of a ceramide with a galactose residue at the 1-hydroxyl moiety.The galactose is cleaved by galactosylceramidase....
s. Galactocerebrosides are typically found in neural tissue, while glucocerebrosides are found in other tissues.
Structure and Function
The fundamental structure of a cerebroside is ceramide. Monoglycosyl and oligoglycosylceramides having a mono or polysaccharide bonded glycosidically to the terminal OH group of ceramide is defined as a cerebroside. Sphingosine is the main long-chain base present in ceramide.Galactosylceramide is the principal glycosphingolipid in brain tissue. Galactosylceramides are present in all nervous tissues, and can compose up to 2% dry weight of grey matter and 12% of white matter. They are major constituents of oligodendrocytes. Glucosylceramide is found at low levels in animal cells such as the spleen, erythrocytes, and nervous tissues, especially neurons. Glucosylceramide is a major constituent of skin lipids, where it is essential for lamellar body formation in the stratum corneum and to maintain the water permeability barrier of the skin. Glucosylceramide is the only glycosphingolipid common to plants, fungi and animals. It is usually considered to be the principal glycosphingolipid in plants. It is a major component of the outer layer of the plasma membrane. Galactosylceramides have not been found in plants.
Monogalactosylceramide is the largest single component of the myelin sheath of nerves.The sugar moiety is linked glycosidically to the C-1 hydroxyl group of ceramide, such as in lactosylceramide. Cerebrosides containing a sulfuric Ester (sulfate) group, known as sulfatides, also occur in the myelin sheath of nerves. These compounds are preferably named as sulfates of the parent glycosphingolipid.
Synthesis
The biosynthesis of monoglycosylceramides requires a direct transfer of the carbohydrate moiety from a sugar-nucleotide, such as uridine 5-diphosphate(UDP)-galactose, or UDP-glucose to the ceramide unit. The glycosyl-transferase catalyzed reaction results in an inversion of the glycosidic bond stereochemistry, changing from α →β. Synthesis of galactosylceramide, and glucosylceramide occurs on the lumenal surface of the endoplasmic reticulum, and on the cytosolic side of the early Golgi membranes respectively.Physical Properties
The melting point (MP) of cerebrosides is considerably greater than physiological body temperature, >37.0 °C, giving glycolipids a paracrystalline, similar to liquid crystal structure. Cerebroside molecules are able form up to eight intermolecular hydrogen bonds between the polar hydrogens of the sugar and the hydroxy and amide groups of the sphingosine base of the ceramide. These hydrogen bonds within the cerebrosides result in the molecules having a high transition temperature and compact alignment. Monoglycosylceramides in conjunction with cholesterol are prevalent in the lipid-raft micro domain, which are important sites in the binding of proteins, and enzyme-receptor interactions.Catabolism
Degradation of glycosphingolipids occurs in the lysosome, which contains digestive enzymes in animal cells. The lysosome breaks down the glycosphingolipid to its primary components, fatty acids, sphingosine, and saccharide.Chemical Analysis
Analysis of monoglycosylceramides can be done by high-resolution thin-layer chromatography, high-performance liquid chromatography (HPLC), and mass spectrometry. Reversed-phase HPLC is now the standard method for separation of molecular species, often after benzoylation, enabling lipids to be detected by UV spectrophotometry.Role in disease
A defect in the degradation of glucocerebrosides is Gaucher's diseaseGaucher's disease
Gaucher's disease is a genetic disease in which a fatty substance accumulates in cells and certain organs.Gaucher's disease is the most common of the lysosomal storage diseases. It is caused by a hereditary deficiency of the enzyme glucosylceramidase. The enzyme acts on the fatty acid...
..The corresponding defect for galactocerebrosides is Krabbe disease
Krabbe disease
Krabbe disease is a rare, often fatal degenerative disorder that affects the myelin sheath of the nervous system. This condition is inherited in an autosomal recessive pattern...
.