Pectinesterase (EC 3.1.1.11) (pectin methylesterase) catalyzes the hydrolysis of pectin into pectate and methanol. In plants, it plays an important role in cell wall metabolism during fruit ripening, cell wall extension and during pollen germination. 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.

Prokaryotic and eukaryotic pectinesterases share a few regions of sequence similarity [1,2,3]. We selected two of these regions as signature patterns. The first is based on a region in the N-terminal section of these enzymes; it contains a conserved tyrosine which may play a role in the catalytic mechanism [3]. The second pattern corresponds to the conserved sequence around an active site aspartate [4], an octapeptide located in the central part of these enzymes.