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

Crystalstructure of a class V chitinase from Arabidopsis thaliana [Arabidopsis thaliana],3AQU_B Crystal structure of a class V chitinase from Arabidopsis thaliana [Arabidopsis thaliana],3AQU_C Crystal structure of a class V chitinase from Arabidopsis thaliana [Arabidopsis thaliana],3AQU_D Crystal structure of a class V chitinase from Arabidopsis thaliana [Arabidopsis thaliana]

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 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]

ChainA, CHITINASE 1 [Coccidioides immitis],1LL4_A Chain A, Chitinase 1 [Coccidioides immitis],1LL4_B Chain B, Chitinase 1 [Coccidioides immitis],1LL4_C Chain C, Chitinase 1 [Coccidioides immitis],1LL4_D Chain D, Chitinase 1 [Coccidioides immitis]

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

Class V chitinase OS=Arabidopsis thaliana OX=3702 GN=ChiC PE=1 SV=1

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

Endochitinase 1 OS=Coccidioides immitis (strain RS) OX=246410 GN=CTS1 PE=3 SV=1

Endochitinase 1 OS=Coccidioides posadasii (strain RMSCC 757 / Silveira) OX=443226 GN=CTS1 PE=1 SV=1