The mechanism of cellulase action on cotton fibers: evidence from atomic force microscopy

Two cellulases from Trichoderma reesei - an exoglucanase, CBH I, and an end oglucanase, EG II - alone and in combination were incubated with cotton fib ers. The effects of the cellulases on the surfaces of the cotton fibers wer e examined by atomic force microscopy. At high magnification, the physical effects on the fibers caused by the two types of enzymes were considerably different. Treatment with CBH I resulted in the appearance of distinct path ways or tracks along the length of the macrofibril. Treatment with EG II ap peared to cause peeling and smoothing of the fiber surface. In combination, their effect was observed to be greatest when both enzymes were present si multaneously. When fibers smoothed by treatment with EG II were treated sub sequently with CBH I, further evidence of path way formation caused by the action of CBH I along the fibers was observed. Incubation with a cellulase from Thermotoga maritima that lacks a cellulose binding domain had no effec t on the surface of cotton fibers. These images provide the first physical evidence of differences in the effect of cellulase components action on the surface of cotton fibers and provide evidence for the movement or tracking of CBH I along the fibers. The first AFM image of CBH I molecules are pres ented. (C) 2000 Elsevier Science B.V. All rights reserved.