Glycolipids are membrane elements in species which range from bacteria to man especially in those organisms which live in uncommon harsh conditions. The most probable function of glycolipids in membrane is based on their capability to go by extensive interlipid hydrogen bonding via glycosyl head groups; consequently they provide architectural reliability to the membranes of the organisms. Besides, being architectural elements of the cell membrane, they play a vital role in cellular roles such as in cell-cell communication, as receptor elements, as anchors for proteins and as regulators of signal transduction.
The term glycolipid represents any compound containing one or more monosaccharide residues limited by a glycosidic linkage to a hydrophobic moiety such as an acylglycerol, a sphingoid, a ceramide (N-acylsphingoid) or a prenyl phosphate. Their role is to provide energy and also serve as markers for cellular identification.
additionally, glycolipids offer a molecular foundation for gathering of signal transducers. The limited relationships between cholesterol and glycolipids in the tissue inner are the strength that segregates them from phospholipids that keep liquid in characteristics.
Classification of Glycolopids:
Glycolipids are categorized as follows:
- Glycoglycerolipids: The term glycoglycerolipid is used to assign glycolipids containing mono, di or trisaccharides attached glycosidically to the hydroxyl band of diglycerides. Monogalactosyl-diacylglycerols and digalactosyldiacylglycerols are the dominant glycolipid elements of the various walls of chloroplasts and also these are the most abundant fats in all photosynthetic cells, such as those of higher plants, plankton and certain bacteria.
- Glycosphingolipids:The term glycosphingolipid represents fats containing at the minimum one monosaccharide residue connected to ceramide moiety. Ceramides are amides of fatty acids with long chain di or trihydroxy bases. The acyl group of ceramides is usually a long chain saturated or monounsaturated fatty acids. Glycosphingolipids are subdivided as follows:
- Neutral glycosphingolipids: These glycolipids constitute one or more glycosyl moieties that come with ceramide e.g. cerebrosides: Cerebrosides are monoglycosylceramides in which glucose or galactose sugar residue is connected by O-ester linkage to the main alcohol of the ceramide. Galactosylceramides are found in all nervous tissues, but they can amount to 2% of the dry bodyweight of brain and 12% of white matter. Glucosylceramide (Glcs1-1’Cer) is found at low stages in animal tissues, such as spleen and erythrocytes, in addition as in nervous tissues.
- Oligoglycosylceramides: Glycosphingolipids containing more than one glucose moiety is supposed to be the oligoglycosylceramide group. They are basic elements of cellular membranes of most eukaryotic organisms and some viruses. The most basic and abundant of the oligosylceramides is β-D-galactosyl-(1-4)-β-D-glucosyl-(1-1′)-ceramide, also known as lactosylceramide (LacCer).
- Sulfoglycosphingolipids: They are sometimes called as “sulfatides” or “sulfatoglycosphingolipids” also. These are glycosphingolipids holding a sulfate ester group connected to the carbohydrate moiety. Sulfated is mainly produced of 3-sulfate esters of galactosylcerebrosides (galactosyl-3-sulfate esters). They are mainly found in cells that are very dynamic in sodium transport such as kidneys, sodium glands and gills.
- Gangliosides: This group of glycosphingolipids comprises of molecules consisting of ceramide connected by a glycosidic bond to an oligosaccharide cycle containing hexose and sialic acid units. These fats can amount to 6% of the body weight of lipids from brain. One of the typical monosialo-gangliosides is ganglioside GM1.
Glycolipids in the cell membranes play a vital role in recognition and signaling activities in a variety of biological occurrences. Recently, studies regarding the natural features of glycolipids and cell surface microdomains (caveolae, lipid rafts, or glycolipid-enriched microdomains) in stem cells are emerging.