The efficient enzymatic degradation of cellulosic biomass relies on the employment of three cellulases i.e., endoglucanases, exoglucanases, and cellobiases. The characterization and understanding of the functional roles of cellobiases from Gram-positive bacterium, Cellulomonas biazotea are quite useful in a variety of industrial applications. This study has mainly centered on the characterization and expression of Cba2 in Escherichia coli and Bacillus subtilis. More than 40% of the β-glucosidase activity detected in the culture medium of C. biazotea was discovered to be occupied by a 100 kD cellobiase which was previously purified and characterized. Therefore, we believe that Cba2 must play a supportive role in the degradation of cellulose in C. biazotea. In this communication, we provi...[ Read more ]

The efficient enzymatic degradation of cellulosic biomass relies on the employment of three cellulases i.e., endoglucanases, exoglucanases, and cellobiases. The characterization and understanding of the functional roles of cellobiases from Gram-positive bacterium, Cellulomonas biazotea are quite useful in a variety of industrial applications. This study has mainly centered on the characterization and expression of Cba2 in Escherichia coli and Bacillus subtilis. More than 40% of the β-glucosidase activity detected in the culture medium of C. biazotea was discovered to be occupied by a 100 kD cellobiase which was previously purified and characterized. Therefore, we believe that Cba2 must play a supportive role in the degradation of cellulose in C. biazotea. In this communication, we provide evidence, for the first time that among the five identified cellobiases of C. biazotea, Cba2 is shown to be the only enzyme possessing a legitimate secretion signal, and it has been found to be a major secretory cellobiase in C. biazotea. In research that combined Cba2, its isoenzymes, as well as other types of cellulases to hydrolyze native cellulosic substrates, Cba2 eventually emerged as a key player. When the five previously characterized and expressed recombinant cellobiases of C. biazotea were mixed individually or in different combinations with recombinant enzyme preparations containing an endoglucanase, CenA, and an exoglucanase, Cex, of another Cellulomonas species, C. fimi, the cellulase mixtures exhibited not only much higher but also synergistically affected activities in filter paper hydrolysis. Among the five C. biazotea cellobiases studied, Cba2 was shown to perform 2.8 to 3.8 times better than other isozymes when acting individually with CenA and Cex. More noteworthy is that when Cba2 and Cba4 were added together to the reaction mixture an even higher synergistic effect was achieved.

The results of cooperativity presented in this work support the potential application of the recombinant approach, whereby Cba2 and other components involved may not only be scalably available but also be tuned flexibly to acquire optimal working conditions, to the development of effective processes for cellulose hydrolysis.