CelE, a multidomain cellulase from Clostridium cellulolyticum: a key enzyme in the cellulosome?

CelE, one of the three major proteins of the cellulosome of Clostridium cel lulolyticum, nas characterized. The amino acid sequence of the protein dedu ced from celE DNA sequence led us to the supposition that CelE Is a three-d omain protein. Recombinant CelE and a truncated form deleted of the putativ e cellulose binding domain (CBD) were obtained. Deletion of the CBD induces a total loss of activity. Exhibiting rather low levels of activity on solu ble, amorphous, and crystalline celluloses, CelE is more active on p-nitrop henyl-cellobiose than the other cellulases from this organism characterized to date. The main product of its action on Avicel is cellobiose (more than 90% of the soluble sugars released), and its attack on carboxymethyl cellu lose is accompanied by a relatively small decrease in viscosity. AU of thes e features suggest that CelE is a cellobiohydrolase which has retained a ce rtain capacity for random, attach mode. We measured saccharification of Avi cel and bacterial microcrystalline cellulose by associations of CelE with f our other cellulases from C. cellulolyticum and found that CelE acts synerg istically with all tested enzymes. The positive influence of CelE activity on the activities of other cellulosomal enzymes may explain its relative ab undance in the cellulosome.