pectinesterase

Recent studies have shown that the manipulation of pectinesterase expression can influence numerous physiological processes.

In plants, pectinesterase plays an important role in cell wall metabolism during fruit ripening.

Pectinesterase catalyses the de-esterification of pectin into pectate and methanol.

Plant pectinesterases are regulated by pectinesterase inhibitors, which are ineffective against microbial enzymes.

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

The N-terminal pro-peptides of pectinesterase are variable in size and sequence and show a low level of amino acid identity.

It has now been shown that some plant pectinesterase isoforms may exhibit both mechanisms and that such mechanisms are driven by alterations in pH.

Homogalacturonan is highly methyl-esterified when exported into cell walls and is subsequently de-esterified by the action of pectinesterase and other pectic enzymes.

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

Pectinesterase catalyses the de-esterification of methyl-esterified D-galactosiduronic acid units in pectic compounds yielding substrates for depolymerising enzymes, particularly acidic pectins and methanol.

The crystal structure of pectinesterase from Erwinia chrysanthemi revealed a beta-helix structure similar to that found in pectinolytic enzymes, though it is different from most structures of esterases.

In plant bacterial pathogens such as Erwinia carotovora and in fungal pathogens such as Aspergillus niger, pectinesterase is involved in maceration and soft-rotting of plant tissue.

During fruit ripening, pectin is broken down by the enzymes pectinase and pectinesterase, in which process the fruit becomes softer as the middle lamellae break down and cells become separated from each other.

The optimal pH of higher plants is usually between pH 7 and pH 8 although the pH of pectinesterase from fungi and bacteria is usually much lower than this.

In plants, pectinesterase plays a role in the modulation of cell wall mechanical stability during fruit ripening, cell wall extension during pollen germination and pollen tube growth, abscission, stem elongation, tuber yield and root development.

A cell wall-associated pectinesterase of Nicotiana tabacum is involved in host cell receptor recognition for the tobacco mosaic virus movement protein and it has been shown that this interaction is required for cell-to-cell translocation of the virus.

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.