Hexosaminidase A cleaves GalNAc from GM2 to form GM3

Stable Identifier
Reaction [transition]
Homo sapiens
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Beta-hexosaminidase A (bHEXA) cleaves the terminal N-acetyl galactosamine from GM2 ganglioside to form GM3 ganglioside (Lemieux et al. 2006). There are two major forms of bHEX: hexosaminidase A and B. The A form is a trimer of the subunits alpha, beta A and beta B. The B form is a tetramer of 2 beta A and 2 beta B subunits (O'Dowd et al. 1988). Only form A is active towards GM2 ganglioside (Conzelmann & Sandhoff 1979). Defects in the two subunits cause lysosomal storage diseases marked by the accumulation of GM2 ganglioside in neuronal cells. Defects in the alpha subunits are the cause of GM2-gangliosidosis type 1 (GM2G1) (MIM:272800), also known as Tay-Sachs disease (Nakano et al. 1988). Defects in the beta subunits are the cause of GM2-gangliosidosis type 2 (GM2G2) (MIM:268800), also known as Sandhoff disease (Banerjee et al. 1991).

Literature References
PubMed ID Title Journal Year
16698036 Crystallographic structure of human beta-hexosaminidase A: interpretation of Tay-Sachs mutations and loss of GM2 ganglioside hydrolysis

Mahuran, DJ, James, MN, Lemieux, MJ, Mark, BL, Withers, SG, Cherney, MM

J Mol Biol 2006
527942 Purification and characterization of an activator protein for the degradation of glycolipids GM2 and GA2 by hexosaminidase A

Sandhoff, K, Conzelmann, E

Hoppe Seylers Z Physiol Chem 1979
1720305 Molecular basis of an adult form of beta-hexosaminidase B deficiency with motor neuron disease

Boyers, MJ, Siciliano, L, Banerjee, P, Oliveri, D, Horwitz, AL, Li, SC, McCabe, NR, Dawson, G

Biochem Biophys Res Commun 1991
2970528 A point mutation in the coding sequence of the beta-hexosaminidase alpha gene results in defective processing of the enzyme protein in an unusual GM2-gangliosidosis variant

Ohno, K, Suzuki, K, Muscillo, M, Hoffman, AJ, Nakano, T

J Neurochem 1988
2971395 Oligosaccharide structure and amino acid sequence of the major glycopeptides of mature human beta-hexosaminidase

Mahuran, D, Gravel, RA, Cumming, DA, O'Dowd, BF

Biochemistry 1988
Catalyst Activity

beta-N-acetylhexosaminidase activity of HEXA [lysosomal lumen]

Orthologous Events
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