Exploitation of plant lignocellulosic biomass is hampered by our ignorance of the molecular basis for its properties such as strength and digestibility. Xylan, the most prevalent non-cellulosic polysaccharide, binds to cellulose microfibrils. The nature of this interaction remains unclear, despite its importance. Here we show that the majority of xylan, which forms a 3-fold helical screw in solution, flattens into a 2-fold helical screw ribbon to bind intimately to cellulose microfibrils in the cell wall. 13C solid-state magic angle spinning NMR spectroscopy, supported by in silico predictions of chemical shifts, shows both 2- and 3-fold screw xylan conformations are present in fresh Arabidopsis stems. The 2-fold screw xylan is spatially close to cellulose, and has similar rigidity to the cellulose microfibrils, but reverts to the 3-fold screw conformation in the cellulose-deficient irx3 mutant. The discovery that induced polysaccharide conformation underlies cell wall assembly provides new principles to understand biomass properties.

Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR

253rd National Meeting (2017)

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