1Biological Chemistry, Weizmann Institute of Science, Rehovot 2Chemical Research Support, Weizmann Institute of Science, Rehovot
The cellulosome is a multi-enzymatic complex that efficiently degrades the plant cell wall. Cel124 is a newly discovered Clostridium thermocellum endoglucanase, with a unique sequence and fold, and it thus belongs to a new GH family. It bears an N-terminal atypical type-I dockerin, which binds preferentially to the cohesin of the cell-envelope protein OlpC, rather than the cohesins in the cellulosomal scaffold protein, CipA. Cel48S is the most abundant exoglucanase and a key component in the cellulosome of C. thermocellum. The combined activity of the targeted Cel48S and Cel124 resulted in a 1.9-fold enhancement of cellulose hydrolysis, compared to the additive value when the two enzymes were used in isolation. The synergism between the family-48 and family-124 cellulases was further investigated in designer cellulosome complexes. The addition of the endoglucanase Cel124 to a divalent designer cellulosome complex containing two family-48 exoglucanases, resulted in a 1.7-fold enhancement of cellulose degrading activity, owing to the contribution of Cel124 and to the synergism induced by the combined proximity and targeting effects.
