3-38: Molecular dynamics investigations of cellulose selectivity of the carbohydrate binding module (CBM) from Cel7a

Cel7a from Hypocrea jecorina is an important enzyme for the saccharification of cellulose and the production of biofuels. Computational modeling can play a key role in achieving a better understanding of the relationship between the molecular structure and the function of the enzyme.  Understanding how the enzyme interacts with the surface of cellulose will lead to strategies for improving its efficiency. In this study, the selectivity of the CAZy family I Carbohydrate-Binding Module (CBM) from Cel7a for the surfaces of crystalline cellulose was investigated using molecular dynamics and molecular mechanics. Potential energies were calculated for the interactions of CBM with the different crystal faces of cellulose. Calculations from an earlier study showed that the potential energy of interaction between the CBM and the (1,0,0) exhibits periodic minima corresponding to the repeat distance of cellobiose residues. No such periodic minima were observed on an equilibrated (0,1,0) surface of cellulose, suggesting that random diffusion on these surfaces is possible. Molecular dynamics simulations were used to explore the movement of the CBM on these surfaces and to investigate preferences for crystalline faces. The results show that this CBM moves from the (0,1,0) surface to the (1,0,0) surface. The molecular interactions responsible for these phenomena will be presented. Taken together, these observations validate the experimentally observed selectivity of this CBM for the (1,0,0) cellulose surface.