Scientific background: |
HEXA(hexosaminidase A (alpha polypeptide)) is an enzyme that in humans is encoded by
the HEXA gene. Hexosaminidase A and the cofactor GM2 activator protein catalyze the degradation of
the GM2 gangliosides and other molecules containing terminal N-acetyl hexosamines The HEXA gene
encodes the alpha subunit of hexosaminidase A , a lysosomal enzyme involved in the breakdown of
gangliosides. The HEXA gene is mapped on 15q23. Even though the alpha and beta subunits of
hexosaminidase A can both cleave GalNAc residues, only the alpha subunit is able to
hydrolyze GM2 gangliosides. The alpha subunit contains a key residue, Arg-424, which is essential for
binding the N-acetyl-neuramanic residue of GM2 gangliosides. Chimeric constructs were expressed in
HeLa cells and selected constructs were produced in the baculovirus expression system to determine
their ability to degrade GM2 ganglioside in the presence of GM2 activator protein. Their results allowed
them to define 2 noncontiguous sequences in the alpha subunit (amino acids 1-191 and 403-529) which,
when substituted into analogous positions in the beta subunit, conferred activity against the sulfated
substrate. |
References: |
1. Akli, S., Chomel, J.-C., Lacorte, J.-M., Bachner, L., Poenaru, A., Poenaru, L. Ten novel mutations in
the HEXA gene in non-Jewish Tay-Sachs patients. Hum. Molec. Genet. 2: 61-67, 1993.
2. Beutler, E., Kuhl, W., Comings, D. Hexosaminidase isozyme in type O Gm2 gangliosidosis
(Sandhoff-Jatzkewitz disease). Am. J. Hum. Genet. 27: 628-638, 1975.
3. Chern, C. J., Beutler, E., Kuhl, W., Gilbert, F., Mellman, W. J., Croce, C. M. Characterization of
heteropolymeric hexosaminidase A in human x mouse hybrid cells. Proc. Nat. Acad. Sci. 73:
3637-3640, 1976. |