Modularity of Cellulases, Xylanases, and Other Glycosyl Hydrolases Relevant for Biomass Degradation

Cellulases and xylanases are glycoside hydrolases essential for the enzymatic deconstruction of plant polysaccharides across environments and in many biotechnological applications. The biochemical characterization of microbial cellulases and xylanases allowed the identification of specific glycoside hydrolase families supporting this process. To date, most characterized cellulases and xylanases consist in a single catalytic domain. However, the identification of more complex enzymatic machinery and the development of comparative genomics together highlighted the structural and functional diversity of enzymes involved in the plant cell wall deconstruction. To degrade complex polysaccharides, microbes produce individual enzymes, sometimes associated with noncatalytic accessory domains, complex proteins with multiple catalytic domains, and noncovalent multiprotein complexes called cellulosomes. In these systems, cellulases and xylanases rely on accessory domains to interact with each other and with their substrate. Here, the association between GH domains encoding potential cellulases and xylanases and their accessory domains is discussed.