Isolation and characterization of a complex forming hydrophilic endoglucanase of Clostridium thermocellum

An endoglucanase (EG5) of Clostridium thermocellum was purified to the homogeneity from the recombinant strains of Escherichia coli. The elution pattern of EG5 on gel filtration column showed the Mr of 100 kDa. However, the SDS-PAGE of the same protein showed the Mr of 35 kDa. This indicates the formation of a soluble trimeric complex by EG5 in non-denaturing conditions. The complex was found to be stable in 100 mM Na-taurocholate or 0.1% (w/v) Nonidet P-40. The hydrophilic nature of EG5 was confirmed by its unretarded elution at high salt concentrations from gel filtration columns. pI of EG5 was determined as 4.75. The EG5 was shown to possess high thermostability (stable at 65 degrees C for several days) and a broad pH range of activity from 5.5 to 7.5. The EG5 was capable of degrading a variety of soluble cellulosic substrates, and was able to enhance the rate and extent of soluble and natural crystalline cellulose hydrolysis by a cellobiohydrolase (CBH3) of C. thermocellum. The combination of properties, like intramolecular complex formation, high thermostability and positive synergistic effect offered by a cellulolytic component of C. thermocellum is being reported for the first time.