Purification and characterization of an endoglucanase from the cellulosomes (multicomponent cellulase complexes) of Clostridium thermocellum

A subunit with carboxymethyl cellulase (CMCase) activity was isolated from the cellulosomes of Clostridium thermocellum after dissociation of the cellulosomes by a mild sodium dodecyl sulfate (SDS) treatment. The subunit displayed only one protein band of 51 kDa on SDS-polyacrylamide gel electrophoresis (SDS-PAGE), but after boiling with SDS it had 3 bands of 60, 56, and 48 kDa. Prolonged incubation with SDS changed the subunit to display exclusively the 48-kDa band after boiling. The 51-kDa subunit was presumably a partially denatured form, and differentiated into 3 species with apparent M(r) of 60, 56, and 48 k through deglycosylation in SDS solution. Enzymatic properties of the 51-kDa subunit resembled those of the endoglucanase A which was purified from the culture fluid and from a E. coli clone with exceptions of temperature and pH optima.