<p>Glycoside hydrolase family 20 <db_xref db="CAZY" dbkey="GH20"/> comprises enzymes with several known activities; beta-hexosaminidase (<db_xref db="EC" dbkey="3.2.1.52"/>); lacto-N-biosidase (<db_xref db="EC" dbkey="3.2.1.140"/>). Carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base in this family of enzymes.</p><p>In the brain and other tissues, beta-hexosaminidase A degrades GM2 gangliosides; specifically, the enzyme hydrolyses terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. There are 3 forms of beta-hexosaminidase: hexosaminidase A is a trimer, with one alpha, one beta-A and one beta-B chain; hexosaminidase B is a tetramer of two beta-A and two beta-B chains; and hexosaminidase S is a homodimer of alpha chains. The two beta chains are derived from the cleavage of a precursor. Mutations in the beta-chain lead to Sandhoff disease, a lysosomal storage disorder characterised by accumulation of GM2 ganglioside [<cite idref="PUB00000654"/>].</p><p>This entry represents the alpha and beta subunit of beta-N-acetylhexosaminidase. It contains a similar fold but lacks the catalytic centre.</p> Acetylhexosaminidase, subunit a/b