- Heteropolysaccharides (also called heteroglycans) are complex carbohydrates composed of two or more different types of monosaccharides covalently linked through glycosidic bonds. Unlike homopolysaccharides, which are built from repeating units of a single sugar, heteropolysaccharides exhibit remarkable structural diversity because they incorporate different monosaccharide residues, such as glucose, galactose, mannose, fucose, xylose, glucuronic acid, or N-acetylated sugars. This diversity in composition and linkage patterns allows heteropolysaccharides to perform a wide array of biological, structural, and functional roles in living systems.
- One of their most prominent roles is in the formation of extracellular matrices (ECM) and connective tissues. In animals, glycosaminoglycans (GAGs) are classic examples of heteropolysaccharides. These include hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate, all of which are composed of repeating disaccharide units that combine amino sugars (such as N-acetylglucosamine or N-acetylgalactosamine) with uronic acids or galactose. GAGs are often covalently linked to proteins, forming proteoglycans, which provide hydration, elasticity, and structural integrity to connective tissues like cartilage, skin, tendons, and the cornea. Their highly charged nature enables them to retain water and resist compressive forces, making them essential for tissue biomechanics.
- In microorganisms, heteropolysaccharides are vital structural and protective components. Many bacteria produce capsular polysaccharides composed of repeating units of multiple sugars and sugar derivatives. These structures form protective capsules around bacterial cells, shielding them from desiccation, host immune responses, and phage attack. They also contribute to bacterial adhesion and virulence. In fungi and algae, complex heteropolysaccharides contribute to the structure of cell walls and extracellular matrices, ensuring mechanical support and environmental adaptability.
- Heteropolysaccharides also play crucial roles in cell recognition, signaling, and immune modulation. For example, glycosaminoglycans and other complex carbohydrates on the cell surface interact with proteins, growth factors, and receptors, influencing processes such as embryonic development, angiogenesis, and immune regulation. The structural variability of heteropolysaccharides, including branching patterns and sulfation levels, creates a molecular “language” that cells use to communicate and regulate biological responses.
- From an industrial and biomedical perspective, heteropolysaccharides are highly valuable materials. Hyaluronic acid is widely used in medicine and cosmetics, particularly in tissue engineering, osteoarthritis treatment, and dermal fillers due to its biocompatibility and viscoelastic properties. Alginate, a heteropolysaccharide derived from brown algae, is used as a thickening, stabilizing, and gelling agent in food, pharmaceuticals, and wound dressings. Similarly, agar and carrageenan, obtained from red algae, are applied extensively in microbiology, biotechnology, and the food industry as solidifying and stabilizing agents.
