Free Energy for Separation of Cellobiose Molecule From a Layer of Cellobiose

Enzymatic hydrolysis is a key step in the production of biofuels using the biochemical platform. The cellulase enzyme complex, which is used in the saccharification process acts synergistically to produce the reaction product, glucose, which can be fermented to ethanol. Cello-oligosaccharides which are the intermediate products formed during the process, are known to attach themselves to the cellulosic surfaces, thus reducing the rate of hydrolysis. In this work, we have investigated the energetics of separation of one cellobiose molecule (repeating unit in cellulose) from a layer of cellobiose molecules. The umbrella sampling technique combined with the weighted histogram analysis method was employed to determine the free energy required for the separation of a pair of cellobiose molecules in water, as well as for the separation of a cellobiose molecule from the cellobiose layer surface. The potential of mean force (PMF) profile for the separation of a cellobiose pair in water exhibited a single minimum with a non-oscillatory profile; the depth of the free energy well for this process was 1.8 kcal/mol. The PMF profile for the separation of a cellobiose molecule from the cellobiose layer surface exhibited a strong minimum with a well depth larger than 20 kcal/mol. The higher value of the well depth in this case results from the increased number of attractive interactions between the cellobiose molecule being considered and the assembly of cellobiose molecules on the surface. The dynamics of the cellobiose molecule near the cellobiose layer surface was also studied using molecular dynamics simulations.