In molecular biology, glycoside hydrolase family 28 is a family

Protein family

A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....

 of glycoside hydrolases

Glycoside hydrolase

Glycoside hydrolases catalyze the hydrolysis of the glycosidic linkage to release smaller sugars...

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Glycoside hydrolases  are a widespread group of enzymes that hydrolyse the glycosidic bond

Glycosidic bond

In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....

 between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families. This classification is available on the CAZy(http://www.cazy.org/GH1.html) web site, and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.

Glycoside hydrolase family 28 CAZY GH_28 comprises enzymes with several known activities; polygalacturonase

Polygalacturonase

Polygalacturonase is an enzyme produced in plants which is involved in the ripening process, and by some bacteria and fungi which is involved in the rotting process. PGs degrades polygalacturonan present in the cell walls of plants by hydrolysis of the glycosidic bonds that link galacturonic acid...

 ; exo-polygalacturonase ; exo-polygalacturonase ; rhamnogalacturonase (EC not defined).

Polygalacturonase (PG) (pectinase) catalyzes 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

Cell wall

The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

 metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 during ripening. In plant bacterial pathogens such as Erwinia carotovora

Erwinia carotovora

Pectobacterium carotovorum is a bacterium of the family Enterobacteriaceae, which is a plant pathogen with a diverse host range. It causes soft rot and blackleg of potato and vegetables as well as slime flux on many different tree species....

or Ralstonia solanacearum

Ralstonia solanacearum

Ralstonia solanacearum is an aerobic non-sporing, Gram-negative plant pathogenic bacterium. R. solanacearum is soil-borne and motile with a polar flagellar tuft. It colonises the xylem, causing bacterial wilt in a very wide range of potential host plants...

(Pseudomonas solanacearum) and fungal pathogens such as Aspergillus niger

Aspergillus niger

Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...

, polygalacturonase is involved in maceration

Maceration

Maceration may refer to:* Maceration , in food preparation* Maceration , a step in wine-making** Carbonic maceration, a wine-making technique* Maceration , in sewage treatment* Maceration , a method of preparing bones...

and soft-rotting of plant tissue. Exo-poly-alpha-D-galacturonosidase (exoPG) hydrolyzes 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.