Arabinose substitution effect on xylan rigidity and self-aggregation

Abstract

Substituted xylans play an important role in the structure and mechanics of the primary cell wall of plants. Arabinoxylans (AX) consist of a xylose backbone substituted with arabinose, while Glucuronoarabinoxylans (GAX) also contain glucuronic acid substitutions and ferulic acid esters on some of the arabinoses. We provide a molecular-level description on the dependence of xylan conformational, self-aggregation properties and binding to cellulose on the degree of arabinose substitution. Molecular dynamics simulations reveal fully solubilized xylans with a low degree of arabinose substitution (lsAX) to be stiffer than their highly substituted (hsAX) counterparts. Small-angle neutron scattering experiment indicate that both wild-type hsAX and debranched lsAX form macromolecular networks that are penetrated by water. In those networks, lsAX are more folded and entangled than hsAX chains. Increased conformational entropy upon network formation for hsAX contributes to AX loss of solubility upon debranching. Furthermore, simulations show the intermolecular contacts to cellulose are not affected by arabinose substitution (within the margin of error). Ferulic acid is the GAX moiety found here to bind to cellulose most strongly, suggesting it may play an anchoring role to strengthen GAX-cellulose interactions. The above results suggest highly substituted GAX acts as a spacer, keeping cellulose microfibrils apart, whereas low substitution GAX is more localized in plant cell walls and promotes cellulose bundling.

Water cast film formability of sugarcane bagasse xylans favored by side groups

“…The side groups of xylan are known to prevent the intermolecular aggregation, which happens for a linear molecule such as cellulose that tends to crystallize. The side groups would thus greatly affect the properties of xylan (Dea et al, 1973;Hoije et al, 2008;Shrestha et al, 2019). The solubility of xylan in water decreased with decreasing number of side groups as the unsubstituted segments would aggregate into insoluble form (Andrewartha et al, 1979).…”

“…Xylan is generally known as an amorphous polymer. However, with reduced number of side groups, xylan can form hydrous and anhydrous crystals (Dea et al, 1973;Hoije et al, 2008;Horio and Imamura, 1964;Kobayashi et al, 2013;Marchessault and Timell, 1960;Nieduszynski and Marchessault, 1972), which greatly hinders the polymer internal rotation and thus increase the rigidity (Arinstein et al, 2007;De Rosa et al, 2006;Fama et al, 2005;Shrestha et al, 2019).…”

Full structural ensembles of intrinsically disordered proteins from unbiased molecular dynamics simulations

“…Simple theories established for semiflexible homopolymers and heteropolymers have been shown to provide a qualitative description of IDP structural properties such as stiffness 67 – 69 and solvent quality 12 , 14 , 55 , 70 , 71 . The high fidelity HREMD trajectories reveal that, despite having markedly different sequences, the IDPs studied here have common hierarchical chain architecture.…”

Breeding Targets to Improve Biomass Quality in Miscanthus

“…However, substitutions at the α-(1→2) position are low in miscanthus, as the amount of α-(1→3)-linked arabinosyl units is between 4 and 6 times higher compared to the amount positioned at the α-(1, →2) position in stems [ 128 ]. Results from another simulation study reported stronger binding of less substituted arabinoxylan to cellulose, but also showed strong binding of ferulic acid to cellulose, proposing that ferulic acid could play an important role in arabinoxylan to cellulose interactions [ 147 ]. Clearly, further research would be needed to confirm if such interactions occur in vivo in the cell walls of miscanthus.…”