Domain-specific lignin–carbohydrate interactions govern cell wall deconstruction in wheat straw

Abstract

Lignocellulosic cell walls represent Earth's largest renewable reservoir of organic carbon, yet their extensive lignin–carbohydrate interactions render them recalcitrant to biorefinery conversion. Although hydrothermal pretreatment offers a paradigmatic route to deconstruct cell walls, the molecular basis underlying how it disrupts lignin–carbohydrate interactions remains elusive. Here, we employ solid-state nuclear magnetic resonance spectroscopy on uniformly ¹³C-labelled wheat straw, using hydration and hydrothermal pretreatments as complementary strategies to reveal domain-specific interaction alterations at atomic resolution. These strategies enable domain-specific characterization of structural molecules, identifying two distinct interaction domains within the cell wall: labile interaction domains, dominated by guaiacyl (G) units that weakly interact with carbohydrates and are readily removed; and stable interaction domains, dominated by syringyl (S) units that strongly interact with carbohydrates and resist deconstruction. Furthermore, the interactions between unflattened three-fold xylan and lignin are disrupted, leading to the detachment of lignin that is anchored onto cellulose surfaces. These alterations in molecular interactions attenuate the dynamics and hydration of cell walls. These findings advance knowledge of the elusive yet efficient deconstruction of lignocellulose in industrial systems, with key implications for next-generation biomass biorefineries.