Glycocalyx is a complex supra-membrane complex that forms a thin shell on the surface of the plasmalemma of animal cells and bacterial cytoplasmic membranes. The term comes from a combination of the Greek and Latin words glykys callum, which literally means "sweet thick skin". Indeed, the glycocalyx acts as an additional cell membrane and is built mainly from molecules of a carbohydrate nature, but unlike the plasma membrane, it has a fleecy rather than a continuous structure.
General characteristics
Glycocalyx is an additional protective layer on the cell surface, formed by molecules of proteins, carbohydrates and lipids attached to the CPM, as well as by the outer parts of proteins embedded in the membrane. The basis of such a cytological cover is a network of glycosides (glycoproteins and proteoglycans).
SoThus, the glycocalyx is a highly charged shell enriched with carbohydrate components, which is a combination of biological macromolecules associated with the membrane. This layer serves as an additional barrier between the cell and the environment and performs many functions, which are divided into stabilizing, protective and specific.
Glycocalyx is characteristic only for prokaryotic organisms and animals. Plant cell membranes do not form such a shell.
Functions
The full set of glycocalyx functions in cells and at the tissue level of macroorganisms is not currently defined. However, it has already been established that this layer:
- participates in signal transduction from the extracellular environment to the intracellular environment;
- protects the cytoplasmic membrane from stress and mechanical influences;
- provides adhesive properties for some cells;
- acts as a recognition factor.
In bacteria, the glycocalyx provides attachment to the surface, prevents moisture loss when it enters a dry environment, and protects against the action of antibacterial substances. In pathogens, this layer can prevent the immune system from detecting the pathogen.
Biochemical composition and structure
Glycocalyx includes:
- proteoglycans (chains of glycosaminoglycans connected to a protein core) - consist of syndicans, glypicans, mimecan, perlacan and biglycans;
- glycosaminoglycans (linear disaccharide polymers of uronic acid and hexosamine) - by 50-90% are composed of heparan sulfate and also include dermatan sulfate, chondroitin sulfate, keratan sulfate and hyaluronan;
- glycoproteins containing acid oligosaccharides and sialic acids;
- various soluble components (proteins, proteoglycans, etc.);
- molecules adsorbed on the surface of the membrane from the extracellular space.
The structure and exact content of the biochemical components of the glycocalyx vary depending on the cell type, as well as the prevailing physical and mechanical environmental conditions.
The use of special dyes makes it possible to visualize this additional shell using electron microscopy.
Endothelial Hycocalyx
Endothelial glycocalyx is a carbohydrate-rich layer lining the luminal surface of blood vessels and forming a rather thick (about 500 nanometers) acellular membrane that performs functions not only at the cytological, but also at the tissue level. This structure was first discovered by Luft 40 years ago.
It is now established that the endothelial glycocalyx is a key determinant of vascular permeability. With regard to blood flow, it has a partially negative charge, which prevents excessive absorption of cellular albumin. The glycocalyx also functions as a mechanical protection for the endothelium.
