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.

A subgroup of the Glycosyl hydrolase family 20 (GH20) catalytic domain found in proteins similar to the N-acetylhexosaminidase from Streptomyces plicatus (SpHex). SpHex catalyzes the hydrolysis of N-acetyl-beta-hexosaminides. An Asp residue within the active site plays a critical role in substrate-assisted catalysis by orienting the 2-acetamido group and stabilizing the transition state. 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. Proteins belonging to this subgroup lack the C-terminal PKD (polycystic kidney disease I)-like domain found in the chitobiases.

Beta-N-acetylhexosaminidases 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. The hexA and hexB genes encode the alpha- and beta-subunits of the two major beta-N-acetylhexosaminidase isoenzymes, N-acetyl-beta-D-hexosaminidase A (HexA) and beta-N-acetylhexosaminidase B (HexB). Both the alpha and the beta catalytic subunits have a TIM-barrel fold and belong to the glycosyl hydrolase family 20 (GH20). The HexA enzyme is a heterodimer containing one alpha and one beta subunit while the HexB enzyme is a homodimer containing two beta-subunits. Hexosaminidase mutations cause an inability to properly hydrolyze certain sphingolipids which accumulate in lysosomes within the brain, resulting in the lipid storage disorders Tay-Sachs and Sandhoff. Mutations in the alpha subunit cause in a deficiency in the HexA enzyme and result in Tay-Sachs, mutations in the beta-subunit cause in a deficiency in both HexA and HexB enzymes and result in Sandhoff disease. In both disorders GM(2) gangliosides accumulate in lysosomes. 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.

Thecrystal structure of beta-N-acetylhexosaminidase from Bacteroides fragilis NCTC 9343 [Bacteroides fragilis NCTC 9343],4PYS_B The crystal structure of beta-N-acetylhexosaminidase from Bacteroides fragilis NCTC 9343 [Bacteroides fragilis NCTC 9343]

Crystalstructure of beta-N-acetylhexosaminidase Am0868 from Akkermansia muciniphila [Akkermansia muciniphila ATCC BAA-835],7CBO_A Crystal structure of beta-N-acetylhexosaminidase Am0868 from Akkermansia muciniphila in complex with GlcNAc [Akkermansia muciniphila ATCC BAA-835]

AGlycoside Hydrolase Family 20 beta-N-Acetylglucosaminidase [Microbacterium sp. HJ5],7BWG_B A Glycoside Hydrolase Family 20 beta-N-Acetylglucosaminidase [Microbacterium sp. HJ5]

Crystalstructure of beta-hexosaminidase from Paenibacillus sp. TS12 [Paenibacillus sp.],3GH5_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with GlcNAc [Paenibacillus sp.],3GH7_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with GalNAc [Paenibacillus sp.],3SUR_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with NAG-thiazoline. [Paenibacillus sp. TS12],3SUS_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with Gal-NAG-thiazoline [Paenibacillus sp. TS12],3SUT_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with PUGNAc [Paenibacillus sp. TS12],3SUU_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with Gal-PUGNAc [Paenibacillus sp. TS12],3SUV_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with NHAc-DNJ [Paenibacillus sp. TS12],3SUW_A Crystal structure of beta-hexosaminidase from Paenibacillus sp. TS12 in complex with NHAc-CAS [Paenibacillus sp. TS12]

X-rayStructure of Flavobacterium johnsoniae chitobiase (FjGH20) [Flavobacterium johnsoniae UW101],6YHH_B X-ray Structure of Flavobacterium johnsoniae chitobiase (FjGH20) [Flavobacterium johnsoniae UW101]

Beta-hexosaminidase Amuc_0868 OS=Akkermansia muciniphila (strain ATCC BAA-835 / DSM 22959 / JCM 33894 / BCRC 81048 / CCUG 64013 / CIP 107961 / Muc) OX=349741 GN=Amuc_0868 PE=1 SV=1

Beta-hexosaminidase OS=Porphyromonas gingivalis (strain ATCC BAA-308 / W83) OX=242619 GN=nahA PE=3 SV=2

Beta-hexosaminidase OS=Vibrio furnissii OX=29494 GN=exoI PE=1 SV=1

Beta-hexosaminidase OS=Emericella nidulans OX=162425 GN=nagA PE=1 SV=1

Beta-hexosaminidase A OS=Caenorhabditis briggsae OX=6238 GN=hex-1 PE=3 SV=2