Characterization of the cellulolytic complex (cellulosome) from Ruminococcus albus

The cellulolytic complex was isolated from the culture supernatant of Ruminococcus albus strain F-40 grown on cellulose by a Sephacryl S-300HR column chromatography. The molecular mass of the cellulolytic complex was found to be larger than 1.5 x 10(6) Da. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that the cellulolytic complex contained at least 15 proteins with molecular weights from 40kDa to 250 kDa. Among them, 11 proteins showed endoglucanase and/or xylanase activities on the zymograms. Immunological analysis using an antiserum raised against the dockerin domain of endoglucanase VII of R. albus (DocVII) suggested that at least 7 proteins in the cellulolytic complex contained a dockerin domain immunoreactive with the anti-Doc-VII antiserum. Furthermore, DocVII was shown to specifically interact with a 40-kDa protein of the cellulolytic complex by Far-Western blot analysis. These results strongly suggest that the cellulolytic complex produced by R. albus resembles the cellulosome specified for the cellulolytic complex of several clostridia such as Clostridium thermocellum and respective components are assembled into the cellulosome by the mechanism common in all of the cellulolytic clostridia, i.e., the cellulosome is formed by the interaction between a dockerin domain of catalytic components and a cohesin domain of a scaffolding protein.