- Polysaccharides from animals represent a diverse group of carbohydrate macromolecules that serve critical roles in structural support, energy storage, lubrication, and cell signaling. Unlike plants and fungi, animals produce fewer types of structural polysaccharides, but the ones they do synthesize are highly specialized, often functioning in connective tissues, extracellular matrices, and intercellular communication.
- These polysaccharides are usually complex, frequently modified with sulfate, acetyl, or amino groups, and are often covalently linked to proteins or lipids, forming glycoproteins, proteoglycans, and glycolipids.
- One of the most important classes of animal polysaccharides is the group of glycosaminoglycans (GAGs), which includes hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate, keratan sulfate, and heparin. These are typically long, unbranched chains of repeating disaccharide units composed of an amino sugar (such as glucosamine or galactosamine) and a uronic acid or galactose. GAGs are usually sulfated, except for hyaluronic acid, and carry strong negative charges, allowing them to bind large amounts of water and cations. As a result, they are essential for maintaining tissue hydration, elasticity, and resilience. In cartilage, for example, chondroitin sulfate and keratan sulfate contribute to resistance against compressive forces, while hyaluronic acid provides lubrication in synovial fluid.
- In the extracellular matrix (ECM), GAGs are usually attached to a core protein, forming proteoglycans such as aggrecan, perlecan, and versican. These macromolecules not only provide structural scaffolding but also regulate cell adhesion, proliferation, migration, and differentiation by interacting with growth factors, cytokines, and cell surface receptors. Heparan sulfate proteoglycans, in particular, are critical mediators of cell–cell and cell–matrix communication, influencing processes such as angiogenesis, wound healing, and neural development.
- Another well-known animal polysaccharide is glycogen, the primary storage form of glucose in animals. Glycogen is a highly branched polymer of glucose linked mainly by α-(1→4) glycosidic bonds with α-(1→6) branches occurring approximately every 8–12 residues. Stored mainly in the liver and skeletal muscles, glycogen serves as a readily mobilizable energy reserve to maintain blood glucose homeostasis and fuel muscle activity. Its unique branched structure allows rapid synthesis and degradation, ensuring efficient energy supply during fasting or exertion.
- Animals also produce polysaccharides with specialized protective and functional roles. For instance, mucopolysaccharides in mucus secretions act as lubricants and barriers against pathogens, contributing to respiratory, gastrointestinal, and reproductive tract defenses. Similarly, glycocalyx-associated polysaccharides on the surfaces of animal cells are vital in immune recognition, fertilization, and cell signaling. These carbohydrate-rich coatings act as identity markers, allowing cells to distinguish self from non-self and mediating communication between cells and their environment.
- From a biomedical perspective, animal polysaccharides are of great importance. Heparin, a highly sulfated GAG, is widely used as an anticoagulant in medicine, preventing blood clot formation during surgeries and in patients at risk of thrombosis. Chondroitin sulfate and hyaluronic acid are used as dietary supplements and in therapeutic formulations for joint disorders such as osteoarthritis. Hyaluronic acid is also employed in cosmetic and dermatological applications for its moisturizing and viscoelastic properties, as well as in drug delivery systems and tissue engineering scaffolds. Advances in glycobiology and glycotechnology have further expanded the use of animal polysaccharides in biomaterials, regenerative medicine, and targeted therapies.
