Journal of Biotechnology 57 (1997) 49-57 Biotechnolo Trichoderma reesei cellobiohydrolase I with an endoglucanase cellulose-binding domain: action on bacterial microcrystalline cellulose Malee Srisodsuk, Janne LehtiG, Markus Linder, Emilio Margolles-Clark, Tapani Reinikainen ‘, Tuula T. Teeri * VTT Biotechnology and Food Research, P.O. Box 1500, FIN-02044 VTT, Finland Received 15 October 1996; received in revised form 7 March 1997; accepted 11 March 1997 Abstract Cellulolytic enzymes consist of distinct catalytic and cellulose-binding domains (CBDs). The presence of a CBD improves the binding and activity of cellulases on insoluble substrates but has no influence on their activities on soluble substrates. Structural and biochemical studies of a fungal CBD from Trichoderma reesei cellobiohydrolase I have revealed a wedge shaped structure with a flat cellulose binding surface containing three essential tyrosine residues. The face of the wedge is strictly conserved in all fungal CBDs while many differences occur on the other face of the wedge. Here we have studied the importance of these differences on the function of the T. reesei CBHI by replacing its CBD by a homologous CBD from the endoglucanase, EGI. Our data shows that, apart from slightly improved affinity of the hybrid enzyme, the domain exchange does not significantly influence the function of CBHI. 0 1997 Elsevier Science B.V. Keywords: Cellulose-binding domain; Endoglucanase; Cellobiohydrolase; Trichoderma reesei Abbreviations: CBD, cellulose binding domain; CBHI, cel- lobiohydrolase 1; EGI, endoglucanase I; CBHI-c, catalytic domain of CBHI; EGI-c, catalytic domain of EGI; CBHI-h, hybrid enzyme with the CBHI-c linked to the CBD of EGI; BMCC, bacterial microcrystalline cellulose. * Corresponding author. Present address: Kungliga Tekniska Hiigskolan, Department of Biochemistry and Bio- technology, S-10 044 Stockholm, Sweden. E-mail: Tuula@ biochem.kth.se ’ Present address: Cultor Ltd., Technology Center, FIN- 02460 Kantvik, Finland. 1. Introduction Most celluloolytic enzymes consist of at least two domains joined together by a glycosylated interdomain linker peptide. The larger catalytic domain contains the active site which carries out general acid catalyzed hydrolysis of the /?-1,4-gly- cosidic bonds in cellulose. The smaller cellulose- binding domain (CBD) improves binding of the 016%1656/97/$17.00 0 1997 El sevier Science B.V. All rights reserved. PII SO1 68-l 656(97)00088-6