InterPro domain: IPR000743

O-Glycosyl hydrolases ( 3.2.1. ) are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [ 1 , 2 ]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) website.

Glycoside hydrolase family 28 GH28 comprises enzymes with several known activities; polygalacturonase ( 3.2.1.15 ); exo-polygalacturonase ( 3.2.1.67 ); exo-polygalacturonase ( 3.2.1.82 ); rhamnogalacturonase (EC not defined).

Polygalacturonase (PG) (pectinase) [ 3 , 4 ] catalyses the random hydrolysis of 1,4-alpha-D-galactosiduronic linkages in pectate and other galacturonans. In fruit, polygalacturonase plays an important role in cell wall metabolism during ripening. In plant bacterial pathogens such as Erwinia carotovora or Ralstonia solanacearum (Pseudomonas solanacearum) and fungal pathogens such as Aspergillus niger, polygalacturonase is involved in maceration and soft-rotting of plant tissue. Exo-poly-alpha-D-galacturonosidase ( 3.2.1.82 ) (exoPG) [ 5 ] hydrolyses peptic acid from the non-reducing end, releasing digalacturonate. PG and exoPG share a few regions of sequence similarity, and belong to family 28 of the glycosyl hydrolases.

1. Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases. Proc. Natl. Acad. Sci. U.S.A. 92, 7090-4
2. Structures and mechanisms of glycosyl hydrolases. Structure 3, 853-9
3. Cloning and DNA sequence analysis of a polygalacturonase cDNA from Aspergillus niger RH5344. Biochim. Biophys. Acta 1087, 104-6
4. DNA sequence analysis of pglA and mechanism of export of its polygalacturonase product from Pseudomonas solanacearum. J. Bacteriol. 172, 3879-87
5. Molecular cloning, nucleotide sequence, and marker exchange mutagenesis of the exo-poly-alpha-D-galacturonosidase-encoding pehX gene of Erwinia chrysanthemi EC16. J. Bacteriol. 172, 4988-95