ROLE OF THE INTERDOMAIN LINKER PEPTIDE OF TRICHODERMA-REESEI CELLOBIOHYDROLASE-I IN ITS INTERACTION WITH CRYSTALLINE CELLULOSE

Cellobiohydrolase I (CBH I), the major component of Trichoderma reesei cellulolytic system, is comprised of a catalytic core domain joined t o a cellulose binding-domain (CBD) by an extended O-glycosylated inter domain linker peptide. Two internal deletions were introduced to the l inker in order to investigate its function particularly in the hydroly sis of crystalline cellulose. Deletion of the first one-third of the l inker, including a putative hinge region, reduces the binding capacity of CBH I in high enzyme coverage but does not affect its enzymatic ac tivity on crystalline cellulose. The longer deletion removing practica lly all of the linker dramatically reduces the rate of crystalline cel lulose degradation even though the enzyme still binds to the substrate . We conclude that sufficient spatial separation of the two domains is required for efficient function of CBH I. It is evident that the pres ence of a functional CBD is increasingly important for CBH I toward hi gher enzyme to cellulose ratios. Our data suggest that the putative hi nge removed by the first deletion facilitates CBD-driven binding and d ense packing of the wild type enzyme on the cellulose surface.