Glycocalyx

Glycocalyx is a general term referring to extracellular polymeric material (glycoprotein)^[1] produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. External to the plasma membrane, all animal cells have a fuzzy coat called the glycocalyx. This coat consists of the carbohydrate moieties of membrane glycolipids and glycoproteins. Only identical twins have chemically identical glycocalices; everyone else is unique. The glycocalyx is a type of identification that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, and invading organisms. The glycocalyx also includes the cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development.^[2] Studies have shown that the glycocalyx plays a role in modulating red blood cell filling in capillaries and it is also believed to be important in many other functions of the vascular system, but studies are ongoing.^[3]

Glycocalyx of bacteria

A glycocalyx, literally "sugar coat", is a network of polysaccharides that project from cellular surfaces, e.g. those of bacteria. It serves to protect the bacterium by creating capsules, or allows the bacterium to attach itself to inert surfaces (like teeth or rocks; e.g. Streptococcus pneumoniae attaches itself to lung cells), prokaryotes, or other bacteria (their glycocalyxes can fuse to envelop the colony).

The glycocalyx can be found just outside the cell wall of a bacterium. A distinct, gelatinous glycocalyx is called a Bacterial capsule, while an irregular, diffuse layer is called a slime layer. Glycocalyx can help protect bacteria from phagocytes. It also helps in the formation of biofilms such as a coating on inert surfaces such as catheters, teeth or rocks.

Glycocalyx in the digestive tract

A glycocalyx can also be found on the apical portion of microvilli within the digestive tract, especially within the small intestine. It creates a meshwork 0.3 micrometers thick and consists of acidic mucopolysaccharides and glycoproteins that project from the apical plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption and includes enzymes secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars.

Functions

• Protection: Cushions the plasma membrane and protects it from chemical injury
• Immunity to infection: Enables the immune system to recognize and selectively attack foreign organisms
• Defense against cancer: Changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them
• Transplant compatibility: Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants
• Cell adhesion: Binds cells together so that tissues do not fall apart
• Inflammation regulation: Glycocalyx coating on endothelial walls in blood vessels prevents leukocytes from rolling/binding in healthy states^[4]
• Fertilization: Enables sperm to recognize and bind to eggs
• Embryonic development: Guides embryonic cells to their destinations in the body

References