Glycosyl hydrolase family 20 (GH20) catalytic domain of N-acetyl-beta-D-glucosaminidase (GcnA, also known as BhsA) and related proteins. GcnA is an exoglucosidase which cleaves N-acetyl-beta-D-galactosamine (NAG) and N-acetyl-beta-D-galactosamine residues from 4-methylumbelliferylated (4MU) substrates, as well as cleaving NAG from chito-oligosaccharides (i.e. NAG polymers). In contrast, sulfated forms of the substrate are unable to be cleaved and act instead as mild competitive inhibitors. Additionally, the enzyme is known to be poisoned by several first-row transition metals as well as by mercury. GcnA forms a homodimer with subunits comprised of three domains, an N-terminal zincin-like domain, this central catalytic GH20 domain, and a C-terminal alpha helical domain. The GH20 hexosaminidases are thought to act via a catalytic mechanism in which the catalytic nucleophile is not provided by solvent or the enzyme, but by the substrate itself.

Glycoside Hydrolase 20C C-terminal domain. This is the C-terminal domain of Glycoside hydrolase 20 C (GH20C) present in S. pneumoniae. GH20C possesses the ability to hydrolyze the beta-linkages joining either N-acetylglucosamine or N-acetylgalactosamine to a wide variety of aglycon residues. The C-terminal domain is commonly known as Domain III is important in dimerization as it forms the primary interface of the dimer. However, there is presently no evidence supporting dimerization as being necessary for catalysis. Domain III is unusual among structurally characterized GH20 enzymes but in GH20 enzymes possessing domain III, dimerization seems to be a conserved feature.

Beta-N-acetylhexosaminidases of glycosyl hydrolase family 20 (GH20) catalyze the removal of beta-1,4-linked N-acetyl-D-hexosamine residues from the non-reducing ends of N-acetyl-beta-D-hexosaminides including N-acetylglucosides and N-acetylgalactosides. These enzymes are broadly distributed in microorganisms, plants and animals, and play roles in various key physiological and pathological processes. These processes include cell structural integrity, energy storage, cellular signaling, fertilization, pathogen defense, viral penetration, the development of carcinomas, inflammatory events and lysosomal storage disorders. The GH20 enzymes include the eukaryotic beta-N-acetylhexosaminidases A and B, the bacterial chitobiases, dispersin B, and lacto-N-biosidase. The GH20 hexosaminidases are thought to act via a catalytic mechanism in which the catalytic nucleophile is not provided by the solvent or the enzyme, but by the substrate itself.

Glycosyl hydrolase family 20, catalytic domain. This domain has a TIM barrel fold.

The chitobiase of Serratia marcescens is a beta-N-1,4-acetylhexosaminidase with a glycosyl hydrolase family 20 (GH20) domain that hydrolyzes the beta-1,4-glycosidic linkages in oligomers derived from chitin. Chitin is degraded by a two step process: i) a chitinase hydrolyzes the chitin to oligosaccharides and disaccharides such as di-N-acetyl-D-glucosamine and chitobiose, ii) chitobiase then further degrades these oligomers into monomers. This GH20 domain family includes an N-acetylglucosamidase (GlcNAcase A) from Pseudoalteromonas piscicida and an N-acetylhexosaminidase (SpHex) from Streptomyces plicatus. SpHex lacks the C-terminal PKD (polycystic kidney disease I)-like domain found in the chitobiases. The GH20 hexosaminidases are thought to act via a catalytic mechanism in which the catalytic nucleophile is not provided by solvent or the enzyme, but by the substrate itself.

GH20C,Beta-hexosaminidase from Streptococcus pneumoniae in complex with PUGNAc [Streptococcus pneumoniae TIGR4]

N-acetyl-B-D-glucosaminidase(GCNA) from Streptococcus gordonii [Streptococcus gordonii],2EPM_X N-acetyl-B-D-glucoasminidase (GCNA) from Stretococcus gordonii [Streptococcus gordonii],2EPN_A N-acetyl-B-D-glucosaminidase (GCNA) from Streptococcus gordonii [Streptococcus gordonii],2EPN_B N-acetyl-B-D-glucosaminidase (GCNA) from Streptococcus gordonii [Streptococcus gordonii],2EPO_A N-acetyl-B-D-glucosaminidase (GCNA) from Streptococcus gordonii [Streptococcus gordonii],2EPO_B N-acetyl-B-D-glucosaminidase (GCNA) from Streptococcus gordonii [Streptococcus gordonii]

GH20C,Beta-hexosaminidase from Streptococcus pneumoniae in complex with Gal-PUGNAc [Streptococcus pneumoniae TIGR4],5A6A_A GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with NGT [Streptococcus pneumoniae TIGR4],5A6A_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with NGT [Streptococcus pneumoniae TIGR4],5A6J_A GH20C, Beta-hexosaminidase from Streptococcus pneumoniae [Streptococcus pneumoniae TIGR4],5A6J_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae [Streptococcus pneumoniae TIGR4],5A6J_C GH20C, Beta-hexosaminidase from Streptococcus pneumoniae [Streptococcus pneumoniae TIGR4],5A6J_D GH20C, Beta-hexosaminidase from Streptococcus pneumoniae [Streptococcus pneumoniae TIGR4],5A6K_A GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with Gal-NGT [Streptococcus pneumoniae TIGR4],5A6K_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with Gal-NGT [Streptococcus pneumoniae TIGR4],5AC5_A GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with GlcNAc [Streptococcus pneumoniae TIGR4],5AC5_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with GlcNAc [Streptococcus pneumoniae TIGR4]

GH20C,Beta-hexosaminidase from Streptococcus pneumoniae in complex with PUGNAc [Streptococcus pneumoniae TIGR4],5A6B_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with PUGNAc [Streptococcus pneumoniae TIGR4],5A6B_C GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with PUGNAc [Streptococcus pneumoniae TIGR4]

GH20C,Beta-hexosaminidase from Streptococcus pneumoniae in complex with GalNAc [Streptococcus pneumoniae TIGR4],5AC4_B GH20C, Beta-hexosaminidase from Streptococcus pneumoniae in complex with GalNAc [Streptococcus pneumoniae TIGR4]

Hexosaminidase D OS=Bos taurus OX=9913 GN=HEXD PE=2 SV=2

Hexosaminidase D OS=Mus musculus OX=10090 GN=Hexd PE=1 SV=1

Hexosaminidase D OS=Homo sapiens OX=9606 GN=HEXD PE=1 SV=3