Caldicellulosiruptor bescii is a thermophilic anaerobic bacterium well-known for its excellent cellulose-degrading ability.We have systematically analyzed the biochemical properties of several multimodular glycoside hydrolases with two separate catalytic domains, i.e.CbCe19A/Ce148A, CbCel9B/Man5A, and CbMan5B/Ce144A.The CBM3b modules in these proteins are important for their efficiency in hydrolyzing crystalline cellulose.We have also characterized xylan-degrading enzymes (xylanases, xylosidase,-glucuronidase, acetyl esterase) and set up a starting thermophilic enzyme cocktail for hemicellulose degradation.We also demonstrate that non-GH proteins are universal enhancers of enzymatic activity of cellulases and hemicellulases.We also show that an N-terminal GH10 domain of a multimodular enzyme has promiscuous substrate specificity, which may help the large enzyme in degrading complex plant cell wall polysaccharides.These achievements collectively underline two features of the C.bescii glycoside hydrolases, i.e.multimodular and substrate promiscuity, which seems to be conserved across the Caldicellulosiruptor species.