CEL1 - A NOVEL CELLULOSE-BINDING PROTEIN SECRETED BY AGARICUS-BISPORUS DURING GROWTH ON CRYSTALLINE CELLULOSE

The cell gene of Agaricus bisporus encodes a protein (CEL1) that has a n architecture resembling the multi-domain fungal cellulases, although the sequence of its putative catalytic core is not matched by any oth er in the protein and nucleic acid data bases. The N-terminal half of the putative catalytic domain of CEL1 was expressed in Escherichia col i as a fusion protein with glutathione-S-transferase. The fusion prote in was used to raise a CEL1-specific antibody. CEL1 was detected as an extracellular 49.8 kDa protein in A. bisporus cellulose-grown culture s, where it bound strongly to cellulose. CEL1 was neither an endogluca nase, a cellobiohydrolase able to hydrolyze fluorogenic cellobiosides, a beta-glucosidase, a xylanase, nor a cellobiose:quinone oxidoreducta se. CEL1 was present in some fractions of culture fluid separated by e lectrophoresis which released soluble sugars from crystalline cellulos e.