A Coarse-Grained Model for Molecular Dynamics Simulations of Native Cellulose

We have constructed a coarse-grained model of crystalline cellulose to be used in molecular dynamics simulations. Using cellobiose from the recently published MARTINI coarse-grained force field for carbohydrates [Lopez, C. A. et al. J. Chem. Theory Comput. 2009, 5, 3195−3210] as a starting point, we have reparameterized the nonbonded interactions to reproduce the partitioning free energies between water and cyclohexane for a series of cellooligomers, cellobiose through cellopentaose. By extrapolating the model to longer cellooligomers, and by assigning special cellulose−cellulose nonbonded interactions, we obtain a model which gives a stable, ordered structure in water that closely resembles the crystal structure of cellulose Iβ. Furthermore, the resulting model is compatible with an existing coarse-grained force field for proteins. This is demonstrated by a simulation of the motion of the carbohydrate-binding domain of the fungal cellulase Cel7A from Trichoderma reesei on a crystalline cellulose surface. The diffusion coefficient at room temperature is calculated at Dl = 3.1 × 10−11 cm2 s−1, which is in good agreement with experimental numbers.