Pectinesterase (EC 3.1.1.11; systematic name pectin pectylhydrolase) is a ubiquitous cell-wall-associated enzyme that presents several isoforms that facilitate plant cell wall modification and subsequent breakdown.

The first being a contribution to the stiffening of the cell wall by producing blocks of unesterified carboxyl groups that can interact with calcium ions forming a pectate gel.

Until recently, it was generally assumed that plant pectinesterases remove methyl esters in a progressive block-wise fashion, giving rise to long contiguous stretches of un-esterified GalA residues in homogalacturonan domains of pectin.

Recently, the systematic sequencing of the Arabidopsis thaliana genome has led to the identification of 66 open reading frames that are annotated as pectinesterases, most of which are encoded as large pre-proproteins.

Currently, the role of the pro-region is unknown although it has been hypothesised that it may act as an intramolecular chaperone, ensuring correct folding or deactivating activity until PE insertion in the cell wall is complete.

Recently, particular attention has been devoted to molecular studies of pectinesterase leading to the characterisation of several related isoforms in various higher plant species.

Such data suggests that pectinesterases are encoded by a family of genes that are differentially regulated in cell type in response to specific developmental or environmental cues.

Isoforms of pectinesterase differ in various biochemical parameters such as relative molecular mass, isoelectric point, optimum pH, substrate affinity, ion-requirement and location.

The first three-dimensional structure solved for a plant pectinesterase was for an isoform from carrot (Daucus carota) root and consists of a right-handed parallel β-helix as seen in all the carbohydrate esterase family CE-8, a transmembrane domain and a pectin binding cleft.