## 2 The Principles and Enzymes Used in EAE
### Components of Plant and Fungal Cell Wall
It is common for L-arabinan and D-galactan to attach to rhamosyl residues. In contrast, galacturonic acid residues are intensively acetylated. Rhamnogalacturonan II is the most complex pectin polysaccharide. In its skeleton, there are four oligosaccharidesaride sidel chains (A-D) and over 20 bonds with 12 different sugars. The A side chain is an octasaccharide that can be methylated. The B side chain can consist of six to nine sugars with different terminal residues and different acetylation degrees. In turn, disaccharides are the C and D side chains [18]. Another important component of cell walls is lignin. It is a non-polysaccharide fraction. Lignin is an amorphous polymer consisting of monomers derived from phenylalanine. This composition is characteristic of vascular plants. In grass, monomers are derived from tyrosine [18]. This complex phenyl biopolymer is found in secondary cell walls in association with cellulose and hemicellulose in such specialized tissues as the cortex, vessels, and fibres. Lignin stops cell growth and is responsible for the mechanical strength of the plant and protection against abiotic stresses as well as pathogens and herbivorous animals [21]. The structure of the cell wall of other natural sources of bioactive molecules, e.g., fungi, is different. In the case of the fungal cell wall, it is based on fibrous carrier polysaccharides that constitute scaffolding for the matrix elements. The structure of the cell wall ensures plasticity and, at the same time, mechanical strength. Fungal hyphae use the force generated by turgor pressure to penetrate the substrate [23]. Fungal cell walls show great variability in their composition and organization. They serve a number of important functions in helping fungi to grow, morphogenise, and survive. Thanks to cell wall sensor proteins, the fungus evaluates and reacts to changes in the environment. In this way, the cell wall provides protection against a range of unfavourable environmental conditions, such as drying, cold, heat, or osmotic stress. It is a protective barrier against microorganisms. The cell wall of pathogenic fungi is responsible both for protection against the defensive systems of host cells and for the adhesive properties needed for invasion. It thus plays a key role in virulence and pathogenicity. The adhesive propertiesare also crucial in the colonization of new environments by fungi. Various polysaccharide polymers, proteins, and carbohydrate-protein complexes may exist in fungal cell walls to form a cross-linked matrix. The main components are chitin, melanin, glycoproteins, \(\beta\)-1,3-glucan, and \(\beta\)-1,6-glucan [23; 24; 25]. However, there are species-specific differences in quantitative, qualitative, and structural aspects [23]. Chitin is a structural polysaccharide composed of linear \(\beta\)-(1,4) N-acetylglucosamine chains [23]. Chitin chains can be hydrogen bonded to form extremely tensile microfibrils, in which chitin molecules are arranged antiparallel to each other. Chitin is largely responsible for the rigidity and integrity of the cell wall but is not an essential ingredient in all types of fungal cells. In some fungi, some chitin is deacetylated and chitosan is formed. This polymer of glucosamine residues has better solubility than chitin [24]. Melanins are high molecular weight pigments consisting of polymerized phenolic and/or indole compounds [23]. These amorphous polymers are located in the cell wall and protect against damage associated with ultraviolet radiation, because they intensively absorb UV light. Melanin, similarly to lignin, provides stiffness, hardening of the cell wall, and protection. Therefore, it can be found in structures exposed to adverse conditions, e.g., fungal ascopores or conidia. Melanin is an important virulence factor; it ensures the strength of conidia during penetration and increases the resistance of fungal cells to lysis in host tissues [24]. Besides the abovementioned most common polymers, there is a large group of species-specific ones.