THE DIFFERENCE IN AFFINITY BETWEEN 2 FUNGAL CELLULOSE-BINDING DOMAINSIS DOMINATED BY A SINGLE AMINO-ACID SUBSTITUTION

Cellulose-binding domains (CBDs) form distinct functional units of mos t cellulolytic enzymes. We have compared the cellulose-binding affinit ies of the CBDs of cellobiohydrolase I (CBHI) and endoglucanase I(EGI) from the fungus Trichoderma reesei. The CBD of EGI had significantly higher affinity than that of CBHI. Four variants of the CBHI CBD were made in order to identify the residues responsible for the increased a ffinity in EGI. Most of the difference could be ascribed to a replacem ent of a tyrosine by a tryptophan on the flat cellulose-binding face.