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Applied and Environmental Microbiology, May 2005, p. 2412-2417, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2412-2417.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Processive Endoglucanase Active in Crystalline Cellulose Hydrolysis by the Brown Rot Basidiomycete Gloeophyllum trabeum

Roni Cohen,^1, Melissa R. Suzuki,² and Kenneth E. Hammel^1,2*

Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53706,¹ Institute for Microbial and Biochemical Technology, USDA Forest Products Laboratory, Madison, Wisconsin 53726²

Received 30 September 2004/ Accepted 9 December 2004

Brown rot basidiomycetes have long been thought to lack the processive cellulases that release soluble sugars from crystalline cellulose. On the other hand, these fungi remove all of the cellulose, both crystalline and amorphous, from wood when they degrade it. To resolve this discrepancy, we grew Gloeophyllum trabeum on microcrystalline cellulose (Avicel) and purified the major glycosylhydrolases it produced. The most abundant extracellular enzymes in these cultures were a 42-kDa endoglucanase (Cel5A), a 39-kDa xylanase (Xyn10A), and a 28-kDa endoglucanase (Cel12A). Cel5A had significant Avicelase activity—4.5 nmol glucose equivalents released/min/mg protein. It is a processive endoglucanase, because it hydrolyzed Avicel to cellobiose as the major product while introducing only a small proportion of reducing sugars into the remaining, insoluble substrate. Therefore, since G. trabeum is already known to produce a ß-glucosidase, it is now clear that this brown rot fungus produces enzymes capable of yielding assimilable glucose from crystalline cellulose.

Present address: Sigma-Aldrich Israel, Ltd., 97770 Jerusalem, Israel.

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