Structural and functional effects of manipulating the degree of methylesterification in a model homogalacturonan with a pseudo-random fungal pectin methylesterase followed by a processive methylesterase

Fabrication of hydrogen-bonded crosslinked hydrogel vitrimer with enhanced self-healing and printability via K+ induced low methyl apple pectin

Low methyl pectin, conventionally extruded as sols and shaped through Ca2+ post-curing, face complexity and high production costs, limiting their application in 3D printing. We developed apple pectin (AP) vitrimer inks with shear-thinning behavior at elevated temperatures and self-supporting properties at low ones, via pectin methyl esterase (PME) modification and K+ induction, aiming to facilitate simpler extrusion 3D printing. PME-modified AP (PME-AP) exhibits a higher affinity for K+ compared to AP, attributed to an 8.76 % reduction in the degree of methyl esterification and a 9.72 % increase in the degree of blockiness. Consequently, 1 % PME-AP forms a robust hydrogel vitrimer characterized by a hardness of 121.33 g and a water holding capacity of 99.50 % at 150 mM K+, a 68 % reduction in K+ concentration requirement over AP gels. Through electrostatic shielding, K+ induces hydrogen-bonded crosslinked vitrimers with stress relaxation within 53 s at 80 °C and self-healing properties with minimal texture reduction (~2 g). These characteristics suggest that the hydrogen bond crosslinked vitrimer network can dynamically reorganize in response to temperature variations, making PME-AP gel ideal for 3D printing applications. This study establishes the groundwork for cost-efficient AP-based extrusion 3D printing.

AtPME17 is a functional Arabidopsis thaliana pectin methylesterase regulated by its PRO region that triggers PME activity in the resistance to Botrytis cinerea

Pectin is synthesized in a highly methylesterified form in the Golgi cisternae and partially de-methylesterified in muro by pectin methylesterases (PMEs). Arabidopsis thaliana produces a local and strong induction of PME activity during the infection of the necrotrophic fungus Botrytis cinerea. AtPME17 is a putative A. thaliana PME highly induced in response to B. cinerea. Here, a fine tuning of AtPME17 expression by different defence hormones was identified. Our genetic evidence demonstrates that AtPME17 strongly contributes to the pathogen-induced PME activity and resistance against B. cinerea by triggering jasmonic acid-ethylene-dependent PDF1.2 expression. AtPME17 belongs to group 2 isoforms of PMEs characterized by a PME domain preceded by an N-terminal PRO region. However, the biochemical evidence for AtPME17 as a functional PME is still lacking and the role played by its PRO region is not known. Using the Pichia pastoris expression system, we demonstrate that AtPME17 is a functional PME with activity favoured by an increase in pH. AtPME17 performs a blockwise pattern of pectin de-methylesterification that favours the formation of egg-box structures between homogalacturonans. Recombinant AtPME17 expression in Escherichia coli reveals that the PRO region acts as an intramolecular inhibitor of AtPME17 activity.