HEXA is the alpha subunit of the lysosomal enzyme beta-hexosaminidase that, together with the cofactor GM2 activator protein, catalyzes the degradation of the ganglioside GM2, and other molecules containing terminal N-acetyl hexosamines. Beta-hexosaminidase is composed of two subunits, alpha and beta, which are encoded by separate genes. Both beta-hexosaminidase alpha and beta subunits are members of family 20 of glycosyl hydrolases. Alpha subunit gene mutations lead to Tay-Sachs disease (GM2-gangliosidosis type I). Recombinant human HEXA protein, fused to His-tag at N-terminus, was expressed in E.coli.