Glycobiohydrolases at the forefront of lignocellulose saccharification: A review on substrate specificities and structure-function properties

Glycobiohydrolases are key components of microbial systems for biomass utilization, attacking the chain ends of biopolymers to produce disaccharide units. While for decades glycobiohydrolases have been investigated against cellulose, starch and chitin, these biocatalysts are brought again to the spotlight thanks to the discovery of novel specificities for hemicellulosic and pectic substrates such as xylan, mannan, levan and galactan. Glycobiohydrolases demonstrate several interesting features that arouse scientific interest, such as the exo-acting catalytic mechanism or, in some cases, a bi-functional exo-/ endo-mode of action, the processive hydrolysis of substrates, and their involvement in the cooperative degradation of recalcitrant polymeric structures. This review summarizes the distinct glycobiohydrolase activities involved in the biodegradation of native polysaccharides. Particular focus is given to the substrate of each enzymatic activity, as well as its functional-structural determinants. Finally, this review aims to identify research gaps regarding the various glycobiohydrolase activities and indicate new potential research perspectives.