β-hexosaminidase: Biosynthesis and processing of the normal enzyme, and identification of mutations causing Jewish Tay-Sachs disease

Abstract

Objectives: This report presents an overview of the nearly 100-year history of the study of Tay-Sachs disease in the Ashkenazi Jewish population. Design and Methods: Each major step leading to our present understanding of the disease are highlighted. Results: The original interest in the cause of this devastating disease in the late 1800s led to the identification of a novel glycolipid, G M2 ganglioside, stored in the neurons of Tay-Sachs patients in the 1930s, and the elucidation of its structure in the 1960s. The identification of the defective isozyme, β-hexosaminidase A, followed in 1968–1969. Elucidation of the subunit structures of the hexosaminidase A (αβ) and B (ββ) isozymes in 1973 and their purification in 1974–1980, led to the characterization of the biosynthesis, assembly, intracellular transport, and posttranslational processing of the two subunits in the 1980s. The ability to purify milligram quantities of the isozymes made possible the isolation of cDNA clones encoding both subunits in 1985, and ultimately the identification of the causes of Jewish Tay-Sachs disease at the genomic DNA level in 1988. Conclusions: Tay-Sachs disease is the major model for lysosomal storage diseases. Similarly, the work done in the 1980s on hexosaminidase has been used as a model for understanding the cell biology of many other lysosomal proteins. Current research encompassing the fields of enzymology, cell biology, and molecular biology is linking genotypes with the clinical phenotypes of patients with Tay-Sachs and related diseases.