(1→3,1→6)-β-D-glucans of yeasts and fungi and their biological activity

Glucans, or polymers of D-glucose linked by (1→3)-β and (1→6)-β glycosidic linkages are the common polysaccharides of the fungal cell wall. They are usually located in the inner part of the wall and play the role of skeletal polysaccharide contributing to the shape and rigidity of the cell wall. The β-glucan molecules are interlinked by the hydrogen bonds and sometimes occur in a complex with other polysaccharides, such as chitin. β-Glucans isolated from the various yeast and fungal species may have different molecular weight or other structural parameters such as degree of branching or the length of the side-chains which may affect their solubility in water. Many fungal β-glucans possess remarkable ability to enhance the immune system, i.e. act as immunomodulators. Numerous studies have demonstrated the activity of β-glucans as biological response modifiers that are able to exert beneficial effect in host by demonstrating antitumor, antibacterial, antiviral and antiparasitic activities. Some studies have attempted to correlate biological activity of individual β-glucans to their spatial structure or helical conformation. However neither such correlation nor the precise mechanism of the activation of the immune system by β-glucans have been unambiguously proven. The present article reviews the existing knowledge on the immunological activity of the fungal β-glucans and provides some recent results on the radioprotective and antimutagenic activity of the β-glucan isolated from the baker's yeast.