We han, e shown that spedfic binding of divalent cations to a polysaechafide polyelectro]ym, leading firm cohesion between the chains, can cause characteristic effects ~n ~e c~rcutar diehroism spectrum which are understandabb in terms of modem theo~, [ l ]. For atginate, tiffs binding is a co-operative p,~o-tess that predominantly in~oNes consecuti~'e ~luro-nale residues. Some other systems ha~e now been inves,~igated in an attempt to formulate a general inSetpretafion of bio]ogics] phenomena of this type. T~e known streng~ and specificity of comp~exafion are explained m termg of an "'egg-box model" which ~s ,derN,ed from our measmemems, the known coordination geometries in mode] compounds, and the requiremen~s roar ~ooperafivity.In pectin, • .the methyl este~ of poly(ga~acturonie acid), the interactions with ca~on.~ is relatively weak because ~he chains are unch~r~ed. In contrasl to the beha~onr of alginates, in which the amplitude diminishes w~th gelatben I ] ], the broad, positive, n ~ ~* Cations are absent, however, and their cha~acte~stic in-quence on the ~ orbha~s is therefore no~ seen. After saponification, the pe!ysacchafide binds Ca 2+ wiih ge~ formation and with a large decrease ~n amplitude of the n -~ .~* band ( fig. 1) which shows a gaussian difference spectrum centered on 208 ~[rn. This is therefore [ l ] explained as a specific bind,~ng of most of the umnam residues m Ca 2+ wNch tends to reverse the sign of the n ~ ~* band. Derivatives that are or,.ly partly saponified, as in "%w me~hoxy pectins" used industr~ally and p~esent in MomeNtal systems, show similar specUoseopic changes during gela~on wi~.~ Ca 2÷, except that an additional peak remains with ~he position (210 nm) and ampfitude expected fo,~ methyl galactaronate Nsidues. Being uncha~ged ~Lhe~,c groups wosld noi pa{~¢ipaie directly in ion bin~!k~ng, and the ~esiduai peak therefore confirms our v~ew that the extreme spectra," changes arise horn ~pecific pert~rbatio~ of bound ~e~idues by proximity of the ionic cha~ge: *~buIed between a nnmbez Of rotations] states about .... Po]ymarin~ionate as well as po]yg~]mmnate an~ ,~(5)--C(5) which, due to ~hc d~rent ofienta~ion~ of polyga~acturona~e sequences can be perturbed spotthe ~emboxy] ehromo~no~e Lq the ~yn~met~Je erl.~i~on-m:enI of ~he ~aga~, ring, ha~e ~ ->~* &rods. of ~arying .

Xylans are the most abundant noncellulosic polysaccharides in lignified secondary cell walls of woody dicots and in both primary and secondary cell walls of grasses. These polysaccharides, which comprise 20–35% of terrestrial biomass, present major challenges for the efficient microbial bioconversion of lignocellulosic feedstocks to fuels and other value-added products. Xylans play a significant role in the recalcitrance of biomass to degradation, and their bioconversion requires metabolic pathways that are distinct from those used to metabolize cellulose. In this review, we discuss the key differences in the structural features of xylans across diverse plant species, how these features affect their interactions with cellulose and lignin, and recent developments in understanding their biosynthesis. In particular, we focus on how the combined structural and biosynthetic knowledge can be used as a basis for biomass engineering aimed at developing crops that are better suited as feedstocks for the bioconversion industry.

Summary Insights into the evolution of plant cell walls have important implications for comprehending these diverse and abundant biological structures. In order to understand the evolving structure–function relationships of the plant cell wall, it is imperative to trace the origin of its different components.The present study is focused on plant 1,4‐β‐xylan, tracing its evolutionary origin by genome and transcriptome mining followed by phylogenetic analysis, utilizing a large selection of plants and algae. It substantiates the findings by heterologous expression and biochemical characterization of a charophyte alga xylan synthase.Of the 12 known gene classes involved in 1,4‐β‐xylan formation, XYS1/IRX10 in plants, IRX7, IRX8, IRX9, IRX14 and GUX occurred for the first time in charophyte algae. An XYS1/IRX10 ortholog from Klebsormidium flaccidum, designated K. flaccidum XYLAN SYNTHASE‐1 (Kf XYS1), possesses 1,4‐β‐xylan synthase activity, and 1,4‐β‐xylan occurs in the K. flaccidum cell wall.These data suggest that plant 1,4‐β‐xylan originated in charophytes and shed light on the origin of one of the key cell wall innovations to occur in charophyte algae, facilitating terrestrialization and emergence of polysaccharide‐based plant cell walls.

We report the automated glycan assembly of oligosaccharides related to the plant cell wall hemicellulosic polysaccharide xyloglucan. The synthesis of galactosylated xyloglucan oligosaccharides was enabled by introducing p-methoxybenzyl (PMB) as a temporary protecting group for automated glycan assembly. The generated oligosaccharides were printed as microarrays, and the binding of a collection of xyloglucan-directed monoclonal antibodies (mAbs) to the oligosaccharides was assessed. We also demonstrated that the printed glycans can be further enzymatically modified while appended to the microarray surface by Arabidopsis thaliana xyloglucan xylosyltransferase 2 (AtXXT2).

Growing plants with modified cell wall compositions is a promising strategy to improve resistance to pathogens, increase biomass digestibility, and tune other important properties. In order to alter biomass architecture, a detailed knowledge of cell wall structure and biosynthesis is a prerequisite. We report here a glycan array‐based assay for the high‐throughput identification and characterization of plant cell wall biosynthetic glycosyltransferases (GTs). We demonstrate that different heterologously expressed galactosyl‐, fucosyl‐, and xylosyltransferases can transfer azido‐functionalized sugar nucleotide donors to selected synthetic plant cell wall oligosaccharides on the array and that the transferred monosaccharides can be visualized “on chip” by a 1,3‐dipolar cycloaddition reaction with an alkynyl‐modified dye. The opportunity to simultaneously screen thousands of combinations of putative GTs, nucleotide sugar donors, and oligosaccharide acceptors will dramatically accelerate plant cell wall biosynthesis research.

Polysaccharides are the most important renewable polymers on Earth and hold an enormous potential for the production of ecofriendly functional materials. In addition to being sustainable, they have superior properties to synthetic polymers, particularly in the biomedical field where biocompatibility and biodegradability are vital. Derivatization of polysaccharides obtained from plant biomass paves the path forward for the design and manufacturing of advanced materials with specific properties adapted to meet definitive needs. However, these advances have been severely limited due to issues with establishing structure− property relationships, which are hampered by the heterogeneity of target polysaccharides and the random distribution of functional groups obtained after their chemical modification. An accurate correlation of structure−property relationships at multiple length scales requires substrates with defined sizes, sequences, and substitution patterns. Such tailor-made polysaccharides may be obtained by implementing a bottom-up approach, starting from monosaccharide or oligosaccharide building blocks followed by their polymerization and substitution through catalysis by different carbohydrate-active enzymes such as glycosynthases, phosphorylases, sucrases, and glycosyltransferases. Recent progress in the enzymatic synthesis of artificial polysaccharides is reviewed, with an emphasis on the potential of the synthesized products, either as new materials or as tools to study structure−property relationships. The obtained information will guide future developments of rationally designed biobased materials for industrial and biomedical applications.

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