THE MODULAR CELLULASE CELZ OF THE THERMOPHILIC BACTERIUM CLOSTRIDIUM-STERCORARIUM CONTAINS A THERMOSTABILIZING DOMAIN

The non-catalytic region of the Clostridium stercorarium cellulase Cel Z (Avicelase I) comprises two protein segments (C and C') grouped into different subfamilies of cellulose-binding domain (CBD) family III. T he C-terminally located family IIIb domain C was identified as a true cellulose-binding domain responsible for anchoring the CelZ enzyme to cellulose. The family IIIc domain C' immediately adjacent to the catal ytic domain was unable to mediate binding to cellulose. A deletion stu dy revealed a lack of independence of this pair of domains: almost the entire C' domain was required to maintain the catalytic activity and the thermostability of the enzyme. (C) 1998 Federation of European Mic robiological Societies. Published by Elsevier Science B.V. All rights reserved.