A CARBOXY-TERMINAL TRUNCATION OF HUMAN ALPHA-GALACTOSIDASE-A IN A HETEROZYGOUS FEMALE WITH FABRY DISEASE AND MODIFICATION OF THE ENZYMATIC-ACTIVITY BY THE CARBOXY-TERMINAL DOMAIN - INCREASED, REDUCED, OR ABSENT ENZYME-ACTIVITY DEPENDING ON NUMBER OF AMINO-ACID-RESIDUES DELETED

Fabry disease is an X-linked disorder of glycosphingolipid metabolism caused by a deficiency of alpha-galactosidase A (alpha-Gal A). We iden tified a novel mutation of alpha-Gal A gene in a family with Fabry dis ease, which converted a tyrosine at codon 365 to a stop and resulted i n a truncation of the carboxy (C) terminus by 65 amino acid (AA) resid ues. In a heterozygote of this family,although the mutant and normal a lleles were equally transcribed in cultured fibroblasts, lymphocyte al pha-Gal A activity was similar to 30% Of the normal control and severe clinical symptoms were apparent. COS-1 cells transfected with this mu tant cDNA showed a complete loss of its enzymatic activity. Furthermor e, those cotransfected with mutant and wildtype cDNAs showed a lower a lpha-Gal A activity than those with wild type alone (similar to 30% of wild type alone), which suggested the dominant negative effect of thi s mutation and implied the importance of the C terminus for its activi ty. Thus, we generated mutant cDNAs with various deletion of the C ter minus, and analyzed. Unexpectedly, alpha-Gal A activity was enhanced b y up to sixfold compared with wild-type when from 2 to 10 AA residues were deleted. In contrast, deletion of 12 or more AA acid residues res ulted in a complete loss of enzyme activity. Our data suggest that the C-terminal region of alpha-Gal A plays an important role in the regul ation of its enzyme activity.