Glycosyl hydrolases family 18.

Glyco_18 domain.

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.

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.

The Bacteroides thetaiotaomicron protein represented by pdb structure 3CO4 is an uncharacterized bacterial member of the family 18 glycosyl hydrolases with homologs found in Flavobacterium, Stigmatella, and Pseudomonas.

Crystalstructure of chitinase (RmChi1) from Rhizomucor miehei (sp p32 2 1, MR) [Rhizomucor miehei],5YUQ_A Chain A, Chintase [Rhizomucor miehei],5YUQ_B Chain B, Chintase [Rhizomucor miehei],7FBT_A Chain A, Chitinase [Rhizomucor miehei]

ChainA, Fungal chitinase from Rhizomucor miehei (SeMet-substituted proteins) [Rhizomucor miehei]

Thecrystal structure of a chitinase CrChi1 from the nematophagous fungus Clonostachys rosea [Clonostachys rosea],3G6M_A crystal structure of a chitinase CrChi1 from the nematophagous fungus Clonostachys rosea in complex with a potent inhibitor caffeine [Clonostachys rosea]

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]

Endochitinase 1 OS=Metarhizium robertsii (strain ARSEF 23 / ATCC MYA-3075) OX=655844 GN=chit1 PE=3 SV=1

Endochitinase 42 OS=Trichoderma harzianum OX=5544 GN=chit42 PE=1 SV=1

Endochitinase 46 OS=Trichoderma harzianum OX=5544 GN=chit46 PE=1 SV=1

Endochitinase 1 OS=Metarhizium anisopliae OX=5530 GN=chit1 PE=1 SV=1

Endochitinase 1 OS=Coccidioides posadasii (strain C735) OX=222929 GN=CTS1 PE=3 SV=1