![]() The cell wall components of fungi can represent a considerable part (up to 40–50%) of their body weight. Based on Fesel and Zuccaro’s model, the chitin layer is located in the cell membrane, while the middle position includes the glucan molecules (α- and β-glucans), and the outermost layer consists of mannoproteins. According to Grün’s model, the cell wall contains different glucans (α- and β-glucans), glycoproteins, and chitin. ![]() The focus of interest is on the cell wall structure of large fungi the “mushroom” category essentially refers to Ascomycetes and Basidiomycetes (the taxa with fruiting bodies). ![]() A newer understanding of the systems of the fungal world (according to which fungi and mushroom-like organisms belong to Protista, Chromista, or Eumycota kingdoms) indicates that the cell wall components of each group are typically different (e.g., cellulose is not a component of the cell wall of Eukaryota fungi). The problem of understanding cell wall composition and structure has been an important mycological question for decades. The cell wall has a role in permeability, in the movement of intracellular enzymes into the environment, and in the uptake of hydrolyzed metabolites from nature. The wall is a very important organelle of fungal cells, having different vital functions: it is responsible for mechanical protection, osmotic conditions, protection from dehydration, binding of distinct molecules, etc. Nowadays, mushrooms (both wild and cultivated taxa) have a dual role, since on the one hand they are increasingly important and valuable foods, and on the other hand, they are sources of active substances of increasing importance (i.e., molecules with biological activity). More and more research and measurement data are being published on the composition and different constituents of mushrooms. This review presents in more detail the glucans of lentinan (from Lentinula edodes), pleuran (from Pleurotus ostreatus), grifolan (from Grifola frondose), schizophyllan (from Schizophyllum commune), and krestin (from Trametes versicolor), along with their main biological effects. The glucan levels of individual fungal taxa (including varieties) differ quantitatively and qualitatively. The glucan contents of the stipe exceed the values of the caps. The biological effect of β-glucan molecules is proportional to the integrity of the tertiary structure. Congo red dye reacts with the tertiary triple helix structure, and the resulting glucan content better reflects the biological value of glucan molecules. True comparisons can only be made using the same method. The two methods used today for glucan determination are the enzymatic and Congo red methods. The biosynthesis of glucans takes place in the cytoplasm, the processes of initiation and then chain extension take place with the help of the glucan synthase enzyme complex (EC 2.4.1.34), and the sugar units are provided by sugar donor UDPG molecules. Different glucans can be isolated from different mushroom species, and several glucan fractions can be obtained. It seems that the existence and integrity of the triple helix structure are criteria for their biological effects. X-ray diffraction studies were the first to determine the triple helix configuration of some glucans. Their molecular weights range from 10 4 to 10 5 Da, and rarely 10 6 Da. Glucans from mushrooms are polysaccharides that contain sugar chains, sometimes of only one kind (glucose), sometimes having several monosaccharide units, and they have two (α and β) anomeric forms (isomers). At the end of the 19th century, but mainly since the middle of the 20th century, progressively more scientific information has been published. Folk medicine (especially in the Far East) used medicinal mushrooms based on previous experience. In addition to the beneficial nutritional properties of mushrooms (mineral elements, favorable proteins, low fat and energy content, pleasant aroma, and flavor), they have a high glucan content. Among these, the homo- or heteropolymeric glucan molecules are decisive, as they not only protect fungal cells but also have broad, positive biological effects on the animal and human bodies. Carbohydrates, including polysaccharide macromolecules, are the main constituents of the fungal cell wall.
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