Carbohydrases

Abstract

The enzymes that catalyze the synthesis and degradation of oligo‐ and polysaccharides are among the most important in the biosphere, because of the key role they play in the global carbon cycle. Thanks to a long and rich history of scientific study, the catalytic mechanisms of the glycoside hydrolases and transglycosylases are generally well understood in terms of enzyme‐substrate interactions and transition state structure. Recent structure‐function studies of polysaccharide lyases have also begun to unravel the secrets of catalysis in these distinct classes of carbohydrate‐active enzymes. Built upon a firm understanding of enzyme structure and mechanism, an impressive number of technological applications highlight the prowess of these biological catalysts.

Oxidoreductive Cellulose Depolymerization by the Enzymes Cellobiose Dehydrogenase and Glycoside Hydrolase 61

“…The canonical enzymatic cellulose hydrolysis scheme involves cellobiohydrolases (CBH) which processively degrade cellulose chains from the ends, producing cellobiose (EC 3.2.1.91 for CBHs that proceed from the nonreducing ends of cellulose chains; there is no assigned EC number for cellobiohydrolases that release cellobiose from the reducing ends), endo-␤-1,4-glucanases (EG; EC 3.2.1.4) which internally clip cellulose, shortening chains, and generating reactive ends for CBH, and ␤-glucosidases (BG; EC 3.2. 1.21) which hydrolyze soluble cellodextrins to glucose, mitigating CBH product inhibition arising from cellobiose (4,10,37,38,40). Hemicellulases, ligninases, and other secreted accessory proteins, such as swollenin, increase the accessibility of cellulose to these hydrolytic cellulase activities (10,2,15,19,27,29,39).…”