Large-Scale Atomistic Simulations of Secondary Plant Cell Walls

The secondary plant cell walls are formed by a complex assembly of cellulose, hemicellulose, and lignin biopolymers, providing mechanical strength to plant growth and support. The amorphous cell wall matrix comprised of lignin- and hemicellulose-coated cellulose fibrils is also responsible for the recalcitrance of plant biomass against enzymatic and non-enzymatic depolymerization processes – a major obstacle to achieving sustainable production of renewable biofuels and other value-added chemicals. Understanding the nanoarchitecture of plant cell walls at a molecular scale has been a long-standing challenge from the experimental and computational points of view due to the lack of experimental information at such length-scales and the inherent complexity of the macromolecular assembly. In recent years, advances in solid state NMR spectroscopy and large-scale molecular dynamics simulation techniques have enabled a much broader understanding of these biomolecular systems. Here, report a large-scale atomistic model of secondary plant cell walls of softwood, which is entirely based on the most recent experimental data regarding the fiber’s composition, hemicellulose types and backbone decoration patterns, as well as the crystalline organization of the cellulose elementary microfibrils. The model, comprising roughly 1 million atoms, was subjected to molecular dynamics simulations to investigate basic structural features of the polymers as well as the structure and dynamics of interstitial water molecules. We also investigated the fiber’s elastic properties by means of tensile and compression strain-tension computational assays. The computed Young’s modulus of our model is consistent with reported experimental measurements.