STRUCTURE AND FUNCTION OF ENDOGLUCANASE-V

CELLULOSE is the major polysaccharide component of plant cell walls an d is the most abundant organic compound on the planet. A number of bac terial1 and fungal2 organisms can use cellulose as a food source, poss essing cellulases (cellobiohydrolases and endoglucanases) that can cat alyse the hydrolysis of the beta-(1,4) glycosidic bonds. They can be c lassified into seven distinct families3. The three-dimensional structu res of members of two of these families are known4,5. Here we report t he structure of a third cellulase, endoglucanase V, whose sequence is not represented in any of the above families. The enzyme is structural ly distinct from the previously determined cellulases but is similar t o a recently characterized plant defence protein6. The active site reg ion resembles that of lysozyme, despite the lack of structural similar ity between these two enzymes.