How Much Do You Know about Glycosaminoglycans?
Glycosaminoglycan (GAG) is a general term for the glycan part of proteoglycan macromolecules. Glycosaminoglycans are large linear polysaccharides composed of repeating disaccharide units, and their main configuration contains amino sugars and uronic acids (glucuronic acid and/or iduronic acid). Glycosaminoglycans can be divided into chondroitin sulfate, dermatan sulfate, keratan sulfate, hyaluronic acid, heparin and heparan sulfate categories.
Characteristics
Glycosaminoglycans are the largest component of the extracellular matrix of molecules in animal tissues, and have a fundamental role in different physiological events. We can find these compounds not only in vertebrates, but also in many invertebrates. Its function is to protect the animal kingdom.
Several sulfated structures of heparin, a glycosaminoglycan found in the liver, skin and lung, can be found in different types of organisms from the most primitive to humans. This determines their active and fundamental involvement in biological processes.
As far as hyaluronic acid is concerned, in humans we find it present in the umbilical cord, connective tissue, synovial fluid, cartilage, blood vessels, and vitreous fluid (gelatinous material found between the lens and the retina of the eye); while in nature, it is only present in mollusks.
Another difference is that chondroitin sulfate in the body is present in skeletal tissue and cartilage, while in other poorly developed animals, chondroitin sulfate is present in a limited form, depending on the structural complexity of the individual and its relationship to certain functions.
In nature, we find that glycosaminoglycans (GAGs) have essential functions in cell growth, their differentiation, cell migration, morphogenesis, and viral or bacterial infection.
In vertebrates, the major glycosaminoglycans are heparin or heparan sulfate, chondroitin sulfate, dermatan sulfate and hyaluronic acid. All of these GAGs are identified by alternating units of aminosugar and hyaluronic acid (which can be glucuronic or iduronic) in the chain.
On the other hand, the amino sugar unit can be either N-acetylglucosamine or N-acetylgalactosamine.
Although the structural units of GAG are usually always the same, the repeats of polysaccharides, heparin and chondroitin sulfate chains require considerable structural variation.
Due to the continuous modification, including sulfation and supersaturation of urate, it forms the basis of various structures with biological activities related to GAG.
The presence of these biomolecules in nature, both in vertebrates and invertebrates, has been well documented. In contrast, GAG has never been found in plants.
In certain bacterial chains, synthetic polysaccharides with the same columnar structure as GAG were observed, but these similar polysaccharides did not bind to the core protein and were only produced on the inner surface of the cytoplasmic membrane.
As far as GAG in animal cells is concerned, they are added to the protein nucleus and form proteoglycans. In this way, bacterial polysaccharides are different.
GAGs belonging to vertebrates have a wide structural diversity. The structures of these biomolecules are extremely different from fish and amphibians to mammals.
Biosynthesis of GAGs structural complexes is regulated, and in specific organs and tissues, different sulfation patterns are temporarily formed during growth and development.
Actually, mutational defects in many genes of the biosynthetic enzymes of GAG can have serious consequences for vertebrates. This is why the expression of GAG and its specific sulfate structure plays a fundamental role in life.
Their function is critical because they are fundamental building blocks of connective tissue, and chains of GAGs are linked covalently to other proteins such as cytokines and chemokines.
Another feature is that they are linked to antithrombin, a protein involved in the coagulation process, so they can inhibit this function, which makes it essential in the treatment of, for example, thrombosis.
This is also interesting in the field of cancer research. The disease or other processes (such as inflammatory processes and infectious diseases) can be stopped by being able to inhibit the binding of GAGs proteins, where GAGs act as receptors for certain viruses of the flavivirus type, such as dengue.
GAGs also belong to the three components of the dermis, the layer below the epidermis of the skin, as well as collagen and elastin. These three elements form a system called the extracellular matrix, which, among other things, allows tissue regeneration and removal of toxins from the body.
GAG is a substance that attracts water to the deep layers of the skin. Hyaluronic acid is one of the best-known glycosaminoglycans and is found in many anti-aging and skin care products. The idea of these creams, lotions and tonics is to increase the moisture in the skin by reducing wrinkles and fine lines.
In addition to its ability to retain water, GAG has high viscosity and low compressibility, making it ideal for protecting skeletal bonding in joints.
This is why they are found in synovial fluid, articular cartilage, heart valves (chondroitin sulfate, the most abundant GAG in the body), skin, pulmonary arteries and liver (heparin with anticoagulant function), tendons and lungs (dermatan sulfate) and cornea and bone (keratin sulfate).
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