Structures of mutants of cellulase Cel48F of Clostridium cellulolyticum in complex with long hemithiocellooligosaccharides give rise to a new view of the substrate pathway during processive action.

An efficient breakdown of lignocellulosic biomass is a prerequisite for the production of second-generation biofuels. Cellulases are key enzymes in this process. We crystallized complexes between hemithio-cello-deca and dodecaoses and the inactive mutants E44Q and E55Q of the endo-processive cellulase Cel48F, one of the most abundant cellulases in cellulosomes from Clostridium cellulolyticum, to elucidate its processive mechanism.