Understanding the role of surface chemical properties of cellulose fibrils in productive cellulase binding during hydrolysis

The molecular scale mechanisms of cellulose hydrolysis is still poorly understood. We recently showed that a stark contrast in the digestibility of Cellulose Iα from two sources–bacterial cellulose from Gluconacetobacter xylinus and algal cellulose from Cladophora aegagropila by Trichoderma reesei Cel7A (TrCel7A) are likely due to differences in reducing-end accessibility in the contrasting fibril architecture. We further demonstrated that mechanically increasing the available reducing ends did not impact the rate of hydrolysis by TrCel7A. The accessibility of these available reducing ends play a big role in cellulose hydrolysis that ultimately affects productive binding releasing sugar; however, little is known about the spatial distribution of accessible reducing ends on cellulose fibrils. TrCel7A binds to the cellulose surface by hydrophobic interactions via its carbohydrate-binding module (CBM) while its catalytic domain (CD) binds individual cellodextrins in its active site predominantly by hydrogen bonding interactions. We hypothesize that a surface chemistry map of the cellulose fibril can reveal the binding sites of TrCel7A by its CBM and where the enzymes may locate an accessible reducing end for productive binding. Moreover we hypothesize that mapping changes to the surface chemistry of the cellulose fibrils due to enzyme action will provide insights into the evolving recalcitrance of the insoluble substrate. We present results from applying chemical force microscopy to quantify the ratio of hydrophilic to hydrophobic areas on cellulose fibrils to understand the role of surface chemical properties on productive and non-productive binding of TrCel7A to cellulose.