Glycoside hydrolase family 19

In molecular biology, Glycoside hydrolase family 19 is a family of glycoside hydrolases EC 3.2.1., which 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 glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families.^[1][2][3] This classification is available on the CAZy web site,^[4][5] and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.^[6][7] y[ _]9

Glycosyl hydrolases family 19
the refined crystal structure of an endochitinase from hordeum vulgare l. seeds to 1.8 angstroms resolution
Identifiers
Symbol	Glyco_hydro_19
Pfam	PF00182
Pfam clan	CL0037
InterPro	IPR000726
PROSITE	PDOC00620
SCOP2	2baa / SCOPe / SUPFAM
CAZy	GH19
CDD	cd00325
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Glycoside hydrolase family 19 CAZY GH_19 comprises enzymes with only one known activity; chitinase (EC 3.2.1.14).

Chitinases^[8] are enzymes that catalyze the hydrolysis of the beta-1,4-N-acetyl-D-glucosamine linkages in chitin polymers. Chitinases belong to glycoside hydrolase families 18 or 19.^[9] Chitinases of family 19 (also known as classes IA or I and IB or II) are enzymes from plants that function in the defence against fungal and insect pathogens by destroying their chitin-containing cell wall. Class IA/I and IB/II enzymes differ in the presence (IA/I) or absence (IB/II) of a N-terminal chitin-binding domain. The catalytic domain of these enzymes consist of about 220 to 230 amino acid residues.

Active site

Active site of gycoside hydrolase family 19 papaya chitinase (PDB: 3cql​).^[10] Conserved residues are shown surrounding the catalytic acid, Glu67. A GlcNAc2 unit binding in the -1 and +1 subsites is shown in narrow stick representation and an arrow indicates the position of the glycosidic oxygen.

GH19 enzymes has a conserved sequence motif ([FHY]-G-R-G-[AP]-ζ-Q-[IL]-[ST]-[FHYW]-[HN]-[FY]-[NY], ζ= hydrophilic amino acid) in its active site.^[11]