Slowdown of Enzymatic Cellulose Conversion Emerges from Cellulase Mode of Action

While numerous studies have implicated both substrate and enzyme factors, the underlying mechanism of this rate limitation has remained unresolved. Here, using bacterial cellulose as a well-defined model substrate, we demonstrate that the reaction slowdown emerges from the specific mode of substrate degradation imposed by the cellulolytic enzyme system.

We introduce nanomechanical mapping by time-lapse in situ atomic force microscopy to characterize at nanometer spatial resolution the change in surface material organization of cellulose due to enzymatic degradation. The layer-by-layer ablation of surface material utilized by fungal cellulases results in the gradual exposure of the nanomechanically stiffer (i.e., more densely organized and hence more resistant) inner core of the cellulose fibrils, which leads to a rapid decline in the conversion rate by these enzymes.