Carbohydrate-binding modules (CBMs) are non-catalytic domains found in glycoside hydrolases that facilitate the recognition and binding of polysaccharides. These modules are crucial for the efficient degradation of insoluble polysaccharides by enzymes, as they enhance enzyme-substrate interactions. CBMs are classified into families based on amino acid sequence similarity, with 39 defined families identified. Each CBM has a specific ligand specificity, ranging from crystalline cellulose to various polysaccharides and glycans. CBMs are often appended to glycoside hydrolases to improve their ability to target and degrade complex polysaccharides. CBMs have three main functions: proximity effect, targeting function, and disruptive function. The proximity effect enhances enzyme-substrate interactions by concentrating enzymes on the polysaccharide surface. The targeting function allows CBMs to recognize specific polysaccharide regions, while the disruptive function can alter polysaccharide structure, enhancing degradation. CBMs are also involved in the recognition of various polysaccharides, including cellulose, xylan, mannan, and starch, and some exhibit 'lectin-like' specificity for cell-surface glycans. CBMs are classified into different fold families, including the β-sandwich, β-trefoil, and Hevein folds. These folds determine the binding specificity and ligand recognition of CBMs. The β-sandwich fold is the most common, while the β-trefoil fold is associated with ricin toxin B-chain. The Hevein fold is found in chitin-binding proteins and is characterized by a small β-sheet and a helix. CBMs are also classified into three types based on their binding specificity: Type A (surface-binding), Type B (glycan-chain-binding), and Type C (small-sugar-binding). Type A CBMs bind to crystalline cellulose and chitin, while Type B CBMs bind to glycan chains, and Type C CBMs bind to small sugars. The binding specificity of CBMs is influenced by the arrangement of aromatic amino acid side chains and the conformation of the ligand. Hydrogen bonding and calcium ions also play a role in CBM ligand recognition. Some CBMs use direct hydrogen bonds to recognize their ligands, while others rely on calcium-mediated coordination. The importance of binding-site topography is highlighted by studies showing that the conformation of the ligand can influence the binding specificity of CBMs. CBMs are also involved in multivalency, where multiple binding sites on a single CBM or multiple CBMs can interact with multiple carbohydrate ligands, increasing the overall affinity. This multivalency is particularly important in thermophilic enzymes, where CBMs can compensate for reduced affinity at high temperatures by having tighter binding. Overall, CBMs are essential for the efficient degradation of polysaccharides by glycoside hydrolases, as theyCarbohydrate-binding modules (CBMs) are non-catalytic domains found in glycoside hydrolases that facilitate the recognition and binding of polysaccharides. These modules are crucial for the efficient degradation of insoluble polysaccharides by enzymes, as they enhance enzyme-substrate interactions. CBMs are classified into families based on amino acid sequence similarity, with 39 defined families identified. Each CBM has a specific ligand specificity, ranging from crystalline cellulose to various polysaccharides and glycans. CBMs are often appended to glycoside hydrolases to improve their ability to target and degrade complex polysaccharides. CBMs have three main functions: proximity effect, targeting function, and disruptive function. The proximity effect enhances enzyme-substrate interactions by concentrating enzymes on the polysaccharide surface. The targeting function allows CBMs to recognize specific polysaccharide regions, while the disruptive function can alter polysaccharide structure, enhancing degradation. CBMs are also involved in the recognition of various polysaccharides, including cellulose, xylan, mannan, and starch, and some exhibit 'lectin-like' specificity for cell-surface glycans. CBMs are classified into different fold families, including the β-sandwich, β-trefoil, and Hevein folds. These folds determine the binding specificity and ligand recognition of CBMs. The β-sandwich fold is the most common, while the β-trefoil fold is associated with ricin toxin B-chain. The Hevein fold is found in chitin-binding proteins and is characterized by a small β-sheet and a helix. CBMs are also classified into three types based on their binding specificity: Type A (surface-binding), Type B (glycan-chain-binding), and Type C (small-sugar-binding). Type A CBMs bind to crystalline cellulose and chitin, while Type B CBMs bind to glycan chains, and Type C CBMs bind to small sugars. The binding specificity of CBMs is influenced by the arrangement of aromatic amino acid side chains and the conformation of the ligand. Hydrogen bonding and calcium ions also play a role in CBM ligand recognition. Some CBMs use direct hydrogen bonds to recognize their ligands, while others rely on calcium-mediated coordination. The importance of binding-site topography is highlighted by studies showing that the conformation of the ligand can influence the binding specificity of CBMs. CBMs are also involved in multivalency, where multiple binding sites on a single CBM or multiple CBMs can interact with multiple carbohydrate ligands, increasing the overall affinity. This multivalency is particularly important in thermophilic enzymes, where CBMs can compensate for reduced affinity at high temperatures by having tighter binding. Overall, CBMs are essential for the efficient degradation of polysaccharides by glycoside hydrolases, as they