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