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.

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.

Endo-beta-N-acetylglucosaminidase D [Carbohydrate transport and metabolism]

Endo-beta-N-acetylglucosaminidase (ENGase) hydrolyzes the N-N'-diacetylchitobiosyl core of N-glycosylproteins. The beta-1,4-glycosyl bond located between two N-acetylglucosamine residues is hydrolyzed such that N-acetylglucosamine 1 remains with the protein and N-acetylglucosamine 2 forms the reducing end of the released glycan. ENGase is a key enzyme in the processing of free oligosaccharides in the cytosol of eukaryotes. Oligosaccharides formed in the lumen of the endoplasmic reticulum are transported into the cytosol where they are catabolized by cytosolic ENGases and other enzymes, possibly to maximize the reutilization of the component sugars. ENGases have an eight-stranded alpha/beta barrel topology and are classified as a family 85 glycosyl hydrolase (GH85) domain. The GH85 ENGases are sequence-similar to the family 18 glycosyl hydrolases, also known as GH18 chitinases. An ENGase-like protein is also found in bacteria and is included in this alignment model.

Glycosyl hydrolase family 85. Family of endo-beta-N-acetylglucosaminidases. These enzymes work on a broad spectrum of substrates.