Isolation and characterization of model homogalacturonans of tailored methylesterification patterns

A very highly methylated homogalacturonan (HG) was produced and further used to generate model HG series. HG samples were characterized with respect to their macromolecular features, to their degree and pattern of methyl-esterification, and to their calcium-binding properties. All HG samples were of similar molar mass. Randomly demethylesterified HG samples (B-series) of DM ≥ 40, exhibiting low degree of blockiness (DB), absolute degree of blockiness (DBabs) and calcium binding properties, were classically obtained by alkali deesterification of the very highly methylated “mother” HG. HGs generated by the action of plant pectin-methylesterase (p-PME) on the very highly methylated “mother” HG (P-series) exhibited high DB, DBabs and calcium binding properties, whatever their DM, in consistency with the presence of few long deesterified blocks of GalA. HGs generated by the action of p-PME on “mother” HGs of DM ∼ 80 arising from the B-series (BP-series) exhibited intermediate DB, DBabs and calcium binding properties, in agreement with the presence of numerous but short deesterified blocks of GalA. Manipulating the initial DM of randomly methyl-esterified “mother” HGs prior to enzymatic blockwise demethylesterification allowed the recovery of various HG types with respect to the length and number of demethylesterified GalA stretches.