Polygalacturonase (EC 3.2.1.15), also known as pectin depolymerase, PG, pectolase, pectin hydrolase, and poly-alpha-1,4-galacturonide glycanohydrolase, is an enzyme that hydrolyzes the alpha-1,4 glycosidic bonds between galacturonic acid residues. Polygalacturonan, whose major component is galacturonic acid, is a significant carbohydrate component of the pectin network that comprises plant cell walls. Therefore, the activity of the endogenous plant PGs works to soften and sweeten fruit during the ripening process. Similarly, phytopathogens use PGs as a means to weaken the pectin network, so that digestive enzymes can be excreted into the plant host to acquire nutrients.

This enzyme’s multiple parallel beta sheets form a helical shape that is called a beta helix. This highly stable structure, thanks to numerous hydrogen bonds and disulfide bonds between strands, is a common characteristic of enzymes involved in the degradation of pectin. The interior of the beta helix is hydrophobic.

X-ray crystallography has been used to determine the three-dimensional structure of several PGs in different organisms. Fungal PGs from Colletotrichum lupini,Aspergillus aculeatus, and Aspergillus niger (PG1 and PG2) have been crystallized. The PGs from bacteria like Erwinia carotovora and Bacillus subtilis have also been crystallized. Because of the significant role PGs play in agriculture and industry, computational molecular modeling has been applied to generate theoretical structures of other important PGs. The experimentally determined crystal structures are used as templates for the computational threading process.

...
Wikipedia