Glycosyl hydrolases family 18.

Glyco_18 domain.

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.

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.

Crystalstructure of the GH18 chitinase ChiB from the chitin utilization locus of Flavobacterium johnsoniae [Flavobacterium johnsoniae UW101]

Crystalstructure of Ostrinia furnacalis Group IV chitinase [Ostrinia furnacalis],6JMB_A Chain A, ofchtiv-allosamidin [Ostrinia furnacalis]

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]

Crystalstructure of a insect group III chitinase (CAD1) from Ostrinia furnacalis [Ostrinia furnacalis],5WV9_A Crystal structure of a insect group III chitinase complex with (GlcNAc)6 (CAD1-(GlcNAc)6) from Ostrinia furnacalis [Ostrinia furnacalis]

Crystalstructure of Ostrinia furnacalis Group IV chitinase [Ostrinia furnacalis]

Acidic mammalian chitinase OS=Homo sapiens OX=9606 GN=CHIA PE=1 SV=1

Chitinase-3-like protein 1 OS=Pongo abelii OX=9601 GN=CHI3L1 PE=2 SV=1

Chitinase-3-like protein 1 OS=Homo sapiens OX=9606 GN=CHI3L1 PE=1 SV=2

Acidic mammalian chitinase OS=Rattus norvegicus OX=10116 GN=Chia PE=2 SV=1

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