## 2 The Principles and Enzymes Used in EAE
### Components of Plant and Fungal Cell Wall  
A plant cell wall is a complex structure serving various functions in the plant cell. Among other things, it is a protective barrier and supports cell division and differentiation. The cell wall is mechanically strong; hence, it can maintain the internal turgor pressure. It shows flexibility in response to stress stimuli and activates genes responsible for enzymes that change the structure of the cell [18]. During plant growth, the primary cell wall, which provides structural integrity by balancing high tensile strength with flexibility needed for cell growth, is formed [18]. Cell walls allow plant cells to achieve large increases in volume and a variety of shapes. When a cell has finished growing, it can build a secondary cell wall to specialize in specific functions depending on the type of cell [19]. The secondary cell wall is stronger and thicker. This structure is located between the cell membrane and the primary cell wall [18]. The secondary cell wall strengthens plant tissues and structures, ensuring impermeability and mechanical reinforcement [19]. Depending on the plant species, cell walls differ in their chemical components and structures. This is related to the evolution and differentiation of their composition to adapt plants to various terrestrial habitats [18]. The major components (>90% dry weight) of the cell wall are polysaccharides. The main biopolymer is cellulose. This insoluble carbohydrate is present in both primary and secondary cell walls. Cellulose is responsible for the wall's mechanical strength [20]. Cellulose-rich cell walls are a hallmark of vascular terrestrial plants. This polysaccharide is called a carrier polymer due to the nanostructure it forms in the cell wall. It consistspredominantly of unbranched chains of multiple D-glucose subunits linked by \(\beta\)-(1,4) bonds [18]. Glucan chains arrange in a specific way, creating an amphiphilic structure. The outward facing hydroxyl groups form two polar surfaces, and the exposed sugar skeleton forms two apolar surfaces [19]. Cellulose chains containing up to 25,000 glucose residues have a high degree of polymerization. These chains combine with hydrogen bonds to form regular assemblies, thus creating ordered microfibrils. The second most common polysaccharide fraction consists of hemicelluloses. These non-cellulosic polysaccharides cross-link cellulosic microfibers, thereby preventing microfibrils from collapsing and sliding over each other [21]. Hemicelluloses are heteropolysaccharides with a low degree of polymerization. They form short branched chains. Various monosaccharides can be present in the hemicellulose structure. Typical components for the hemicellulose chain are glucose, mannose, and xylose linked by \(\beta\)-(1\(\rightarrow\)4) bonds. They usually combine with other components of the cell wall through ionic and hydrophobic interactions as well as covalent or hydrogen bonds [22]. Pectins are branched heteropolysaccharides found in the cell wall. They contain acidic (e.g., galacturonic acid and glucuronic acid) and neutral monosaccharides (e.g., rhamnose, galactose, and arabinose). Pectins are mainly found in primary plant cells and in laminae. They provide rigidity and integrity to plant tissues. Pectins participate in intercellular adhesion and maintain the water level in the walls of plant cells. They take part in the defence mechanisms of the cell wall against pathogens. Galacturonic acid is the most common monosaccharide in pectin chains. The most abundant pectin structural polymer is homogalacturonan. This chain consists of galacturonic acid units linked linearly by an \(\alpha\)-1,4 bond. Other common pectin polysaccharides are rhamnogalacturonan I and ramnogalacturonan II [21]. The skeleton of rhamnogalacturonan I is composed of repeatable disaccharide units, which include galacturonic acid combined with rhamnose. Rhamnogalacturonan I shows structural flexibility in different types of cells and at different levels of development.