Plant cell walls are highly complex materials consisting in an intricate network of biopolymers among which hemicellulose represent a major family components displaying a large variations in composition and structure. Among the important structural feature of hemicellulose, acetyl esterification is an ubiquist substitution among hemicellulose families. It usually occurs on O-2 and/or O-3 of xylan. In Planta alteration of xylan acetyl esterification impact severely the plant phenotype and its resistance to biotic stresses. On an applied aspect, decreasing xylan acetyl esterification improves enzymatic saccharification in the biorafinery of lignocellulosic biomass.<br/>The present study focuses on the role of acetyl ester decorations on xylan interaction with cellulose. Acetyl esters are lost by classical alkaline hemicellulose extractions but acetylated xylans can be recovered by DMSO doped by lithium chloride. In this work, interaction of acetylated and deacetylated xylan-enriched fractions obtained by this approach from apple pomace was assessed on model cellulose surface by quartz crystal microbalance with dissipation (QCM-D). Adsorption of xylan fractions were found to be kinetically driven. The acetylation induces the formation of rigid layer of the cellulose surface suggesting an enhanced interaction when compared to non acetylated fractions.<br/>Molecular modelling has then been used to provide a description of the adsorption mechanism at the atomic scale. We have generated various models made of a cellulose microfibril, several chains of xylan that are either native (non-substituted) or acetylated, and water. Models show that the unsubstituted xylan chains has a tendency to modify their conformation when adsorbed on cellulose, going from their preferred three-fold helical form in water solution to the two-fold helix, complementary to that of the cellulose chains. This conformational adaptation was however limited to the xylan chains in direct contact with cellulose, the other chains kept their three-fold conformation. Besides, the xylan fraction in the complex is highly hydrated. In contrast, there has been no significant conformational change for the acetylated xylans, they preferentially explored the two-fold helical conformation in both water solution and adsorbed on cellulose. The acetylated xylan fraction is dense and contains only a small quantity of water molecules in agreement with the QCM-D data.

Impact of xylan acetylation on interaction with cellulose

2019 Spring National Meeting

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