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.

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.

Trehalose utilisation. This family consists of several bacterial ThuA like proteins. ThuA appears to be involved in utilisation of trehalose. The thuA and thuB genes form part of the trehalose/sucrose transport operon thuEFGKAB, which is located on the pSymB megaplasmid. The thuA and thuB genes are induced in vitro by trehalose but not by sucrose and the extent of its induction depends on the concentration of trehalose available in the medium.

Structuralinsights into a novel glycoside hydrolase family 18 N-acetylglucosaminidase from Paenibacillus barengoltzii [Paenibacillus barengoltzii]

ChainA, Putative chitinase II [Klebsiella pneumoniae subsp. pneumoniae MGH 78578]

ChainAAA, Peroxiredoxin [Clostridioides difficile 630]

ChainAAA, Peroxiredoxin [Clostridioides difficile 630]

Crystalstructure of Chitinase D from Serratia proteamaculans at 1.45 Angstrom resolution [Serratia proteamaculans 568],4Q22_A Crystal structure of Chitinase D from Serratia proteamaculans in complex with N-acetyl glucosamine at 1.93 Angstrom resolution [Serratia proteamaculans 568]

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

Chitotriosidase-1 OS=Homo sapiens OX=9606 GN=CHIT1 PE=1 SV=1

Chitotriosidase-1 OS=Mus musculus OX=10090 GN=Chit1 PE=1 SV=2

Probable chitinase 2 OS=Drosophila melanogaster OX=7227 GN=Cht2 PE=1 SV=1

Chitinase 1 OS=Aphanocladium album OX=12942 GN=CHI1 PE=1 SV=2