The adsorption of xyloglucan on cellulose: Effects of explicit water and side chain variation

The interaction between para-crystalline cellulose and the cross-linking glycan xyloglucan (XG) plays a central role for the strength and extensibility of plant cell walls. The coating of XGs on cellulose surfaces is believed to be one of the most probable interaction patterns. In this work, the effects of explicit water and side chain variation on the adsorption of XGs on cellulose are investigated by means of atomistic molecular dynamics simulations. The adsorption properties are studied in detail for three XGs on cellulose Iβ 1-10 surface in aqueous environment, namely GXXXGXXXG, GXXLGXXXG, and GXXFGXXXG, which differ in the length and composition of one side chain. Our work shows that when water molecules are included in the theoretical model, the total interaction energies between the adsorbed XGs and cellulose are considerably smaller than in vacuo. Furthermore, in water environment the van der Waals interactions prevail over the electrostatic interactions in the adsorption. Variation in one side chain does not have significant influence on the interaction energy and the binding affinity, but does affect the equilibrium structural properties of the adsorbed XGs to facilitate the interaction between both the backbone and the side chain residues with the cellulose surface. Together, this analysis provides new insights into the nature of the XG-cellulose interaction, which helps to further refine current molecular models of the composite plant cell wall.