Characterization of the cellulolytic complex (cellulosome) produced by Clostridium cellulolyticum.

The cellulolytic complex was isolated from Clostridium cellulolyticum grown on cellulose. Upon gel filtration, the complex was found to consist mainly of 600-kDa units, along with a 16-MDa aggregate. Its ability to degrade various substrates and its capacity to bind to the crystalline cellulose were measured. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, N-terminal sequencing, and blotting analysis showed that all of the known cellulases of this organism are present in this complex. Three major components were observed: the first component, a noncatalytic, large (160-kDa) protein, was identified based on its ability to bind to the dockerin-containing cellulases as scaffolding protein CipC. The other two components, which had molecular masses of 94 and 80.6 kDa, were identified as CelE and CelF, respectively. The identified cellulases and some other components of the cellulosome were able to bind to a miniCipC1 construct. In addition to providing an extensive description of the system, the results of the present study confirm that the dockerin-cohesin domain interaction plays an essential role in the constitution of the cellulosome.