Direct Evidence for Aligned Binding of Cellulase Enzymes to Cellulose Surfaces

The conversion of biomass into green fuels and chemicals is of great societal interest. Engineers have been designing new cellulase enzymes for the breakdown of otherwise insoluble cellulose materials. A barrier to the rational design of new enzymes has been our lack of a molecular picture of how cellulase binding occurs. A critical factor is the attachment via the enzyme's carbohydrate binding module (CBM). To elucidate the structural and mechanistic details of cellulase adsorption, we have combined experimental data from sum frequency generation spectroscopy with molecular dynamics simulations to probe the equilibrium structure and surface alignment of a 14-residue peptide mimicking the CBM. The data show that binding is driven by hydrogen bonding and that tyrosine side chains within the CBM align the cellulase with the registry of the cellulose surface. Such an alignment is favorable for the translocation and effective cellulose breakdown and is therefore likely an important parameter for the design of novel enzymes.