Restoration of cellulase activity in the inactive cellulosomal protein Cel9V from Ruminiclostridium cellulolyticum

Ruminiclostridium cellulolyticum produces extracellular cellulosomes which contain interalia numerous family‐9 glycoside hydrolases, including the inactive Cel9V. The latter shares the same organization and 79% sequence identity with the active cellulase Cel9E. Nevertheless, two aromatic residues and a four‐residue stretch putatively critical for the activity are missing in Cel9V. Introduction of one Trytophan and the four‐residue stretch restored some weak activity in Cel9V, whereas the replacement of its catalytic domain by that of Cel9E generated a fully active cellulase. Altogether our data indicate that a series of mutations in the catalytic domain of Cel9V lead to an essentially inactive cellulase.