Endo-beta-N-acetylglucosaminidases are bacterial chitinases that hydrolyze the chitin core of various asparagine (N)-linked glycans and glycoproteins. The endo-beta-N-acetylglucosaminidases have a glycosyl hydrolase family 18 (GH18) catalytic domain. Some members also have an additional C-terminal glycosyl hydrolase family 20 (GH20) domain while others have an N-terminal domain of unknown function (pfam08522). Members of this family include endo-beta-N-acetylglucosaminidase S (EndoS) from Streptococcus pyogenes, EndoF1, EndoF2, EndoF3, and EndoH from Flavobacterium meningosepticum, and EndoE from Enterococcus faecalis. EndoS is a secreted endoglycosidase from Streptococcus pyogenes that specifically hydrolyzes the glycan on human IgG between two core N-acetylglucosamine residues. EndoE is a secreted endoglycosidase, encoded by the ndoE gene in Enterococcus faecalis, that hydrolyzes the glycan on human RNase B.

Putative glycoside hydrolase Family 18, chitinase_18. This DUF is likely to be a form of glycosyl hydrolase from CAZy family 18, possibly chitinase 18. This would have the EC number of EC:3.2.1.14.

The GH18 (glycosyl hydrolase, family 18) type II chitinases hydrolyze chitin, an abundant polymer of beta-1,4-linked N-acetylglucosamine (GlcNAc) which is a major component of the cell wall of fungi and the exoskeleton of arthropods. Chitinases have been identified in viruses, bacteria, fungi, protozoan parasites, insects, and plants. The structure of the GH18 domain is an eight-stranded beta/alpha barrel with a pronounced active-site cleft at the C-terminal end of the beta-barrel. The GH18 family includes chitotriosidase, chitobiase, hevamine, zymocin-alpha, narbonin, SI-CLP (stabilin-1 interacting chitinase-like protein), IDGF (imaginal disc growth factor), CFLE (cortical fragment-lytic enzyme) spore hydrolase, the type III and type V plant chitinases, the endo-beta-N-acetylglucosaminidases, and the chitolectins. The GH85 (glycosyl hydrolase, family 85) ENGases (endo-beta-N-acetylglucosaminidases) are closely related to the GH18 chitinases and are included in this alignment model.

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.

Cortical fragment-lytic enzyme (CFLE) is a peptidoglycan hydrolase involved in bacterial endospore germination. CFLE is expressed as an inactive preprotein (called SleB) in the forespore compartment of sporulating cells. SleB translocates across the forespore inner membrane and is deposited as a mature enzyme in the cortex layer of the spore. As part of a sensory mechanism capable of initiating germination, CFLE degrades a spore-specific peptidoglycan constituent called muramic-acid delta-lactam that comprises the outer cortex. CFLE has a C-terminal glycosyl hydrolase family 18 (GH18) catalytic domain as well as two N-terminal LysM peptidoglycan-binding domains. In addition to SleB, this family includes YaaH, YdhD, and YvbX from Bacillus subtilis.

BT1044SeMetE190Q [Bacteroides thetaiotaomicron]