The GH18 (glycosyl hydrolases, family 18) type II chitinases hydrolyze chitin, an abundant polymer of N-acetylglucosamine and have been identified in bacteria, fungi, insects, plants, viruses, and protozoan parasites. The structure of this domain is an eight-stranded alpha/beta barrel with a pronounced active-site cleft at the C-terminal end of the beta-barrel.

Glyco_18 domain.

Chitinase, GH18 family [Carbohydrate transport and metabolism].

Glycosyl hydrolases family 18.

This conserved domain family includes a large number of catalytically inactive chitinase-like lectins (chitolectins) including YKL-39, YKL-40 (HCGP39), YM1, oviductin, and AMCase (acidic mammalian chitinase), as well as catalytically active chitotriosidases. The conserved domain is an eight-stranded alpha/beta barrel fold belonging to the family 18 glycosyl hydrolases. The fold has a pronounced active-site cleft at the C-terminal end of the beta-barrel. The chitolectins lack a key active site glutamate (the proton donor required for hydrolytic activity) but retain highly conserved residues involved in oligosaccharide binding. Chitotriosidase is a chitinolytic enzyme expressed in maturing macrophages, which suggests that it plays a part in antimicrobial defense. Chitotriosidase hydrolyzes chitotriose, as well as colloidal chitin to yield chitobiose and is therefore considered an exochitinase. Chitotriosidase occurs in two major forms, the large form being converted to the small form by either RNA or post-translational processing. Although the small form, containing the chitinase domain alone, is sufficient for the chitinolytic activity, the additional C-terminal chitin-binding domain of the large form plays a role in processing colloidal chitin. The chitotriosidase gene is nonessential in humans, as about 35% of the population are heterozygous and 6% homozygous for an inactivated form of the gene. HCGP39 is a 39-kDa human cartilage glycoprotein thought to play a role in connective tissue remodeling and defense against pathogens.

ChainA, Chitinase A [Serratia marcescens],1X6L_A Chain A, Chitinase A [Serratia marcescens],1X6N_A Chain A, Chitinase A [Serratia marcescens]

CrystalStructure Of Chitinase A From S. Marcescens At 1.55 Angstroms [Serratia marcescens],1FFQ_A Crystal Structure Of Chitinase A Complexed With Allosamidin [Serratia marcescens]

ChitinaseA from Serratia marcescens ATCC990 in complex with Chitotrio-thiazoline dithioamide. [Serratia marcescens]

ChitinaseA from Serratia marcescens ATCC990 in complex with Chitotrio-thiazoline. [Serratia marcescens],2WLZ_A Chitinase A from Serratia marcescens ATCC990 in complex with Chitobio- thiazoline. [Serratia marcescens],2WM0_A Chitinase A from Serratia marcescens ATCC990 in complex with Chitobio- thiazoline thioamide. [Serratia marcescens]

CRYSTALSTRUCTURE OF A BACTERIAL CHITINASE AT 2.3 ANGSTROMS RESOLUTION [Serratia marcescens]

Chitinase A OS=Serratia marcescens OX=615 GN=chiA PE=1 SV=3

Chitinase A OS=Pseudoalteromonas piscicida OX=43662 GN=chiA PE=1 SV=1

Probable endochitinase OS=Orgyia pseudotsugata multicapsid polyhedrosis virus OX=262177 GN=ORF124 PE=3 SV=1

Chitinase OS=Autographa californica nuclear polyhedrosis virus OX=46015 GN=CHIA PE=1 SV=1

Chitinase A1 OS=Niallia circulans OX=1397 GN=chiA1 PE=1 SV=1