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.

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.

Glycosyl hydrolases family 18.

Chitinase, GH18 family [Carbohydrate transport and metabolism].

Crystalstructure of W50A mutant of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis],6KXN_B Crystal structure of W50A mutant of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis]

Crystalstructure of the catalytic domain of chitinase ChiL from Chitiniphilus shinanonensis (CsChiL) [Chitiniphilus shinanonensis],6KST_B Crystal structure of the catalytic domain of chitinase ChiL from Chitiniphilus shinanonensis (CsChiL) [Chitiniphilus shinanonensis],6KXL_A Crystal structure of the catalytic domain of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis],6KXL_B Crystal structure of the catalytic domain of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis]

Crystalstructure of D157N mutant of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis],6KXM_B Crystal structure of D157N mutant of Chitiniphilus shinanonensis chitinase ChiL (CsChiL) complexed with N,N'-diacetylchitobiose [Chitiniphilus shinanonensis]

ChainA, Glycosyl Hydrolase [Niallia circulans]

ChitinaseChiA74 from Bacillus thuringiensis [Bacillus thuringiensis],6BT9_B Chitinase ChiA74 from Bacillus thuringiensis [Bacillus thuringiensis]

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

Probable endochitinase OS=Caenorhabditis elegans OX=6239 GN=cht-1 PE=1 SV=1

Endochitinase OS=Manduca sexta OX=7130 PE=2 SV=1

Endochitinase B1 OS=Neosartorya fumigata OX=746128 GN=chiB1 PE=1 SV=1

Endochitinase B1 OS=Neosartorya fumigata (strain ATCC MYA-4609 / Af293 / CBS 101355 / FGSC A1100) OX=330879 GN=chiB1 PE=3 SV=1