The endo-exo-1,4- #beta# -gluancse Cela of anaerocellum thermophilum contains two catalytic domains. The enzyme was purified an the sequence of the celA gene was determined. Separate cloning and characterization of the domains shows a remarkable celluloytic activity of both catalytic regons. Nevertheless, the activity of full-length CelA on crstalline substrates is significantly higher than that of a mixture of the single components. Like the natural occuring counterpart, we fused the exoglucanase CelY and the endoglucanase CelZ of Clostridium stterocrarium. Compared to a mixture of the avicelases the celluloytic activity of the engineered protein is drastically enhanced. This indicates, analogous to CelA, and efficient intramole-cular synergism of the two catalytic regions.
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