Defective expression of α-L-fucosidase by lymphoid cells of a fucosidosis patient

Fucosidosis is an inherited lysosomal storage disease due to a deficiency of α-L-fucosidase activity. Exponentially growing lymphoid cell cultures from a fucosidosis patient (JH) had 16-fold lower extracellular α-L-fucosidase protein and 72-fold lower intracellular α-L-fucosidase protein with negligible catalytic activity as compared with the mean of 19 control cultures. The percentage of total α-L-fucosidase protein released extracellularly by JH cells was 71% as compared with 35% ± 9% for control cells. During a 1.5 h pulse with 35 S-methionine, α-L-fucosidase was synthesized by JH cells as an intracellular doublet with M r of 58,000 and 56,000 and by control cells as an intracellular form with M r = 58,000. During a subsequent 21 h chase with unlabeled methionine, JH α-L-fucosidase was entirely secreted. In contrast, only 25%–30% of control enzyme was secreted with the remainder retained intracellularly. Thus, JH lymphoid cells synthesized a reduced amount of α-L-fucosidase that was catalytically inefficient and was hypersecreted. Treatment of JH α-L-fucosidase with N-glycanase produced polypeptide chains with M r of 52,000 and 54,000. Previously, treatment of control α-L-fucosidase with N-glycancase produced a single polypeptide chain with M r of 52,000 ( Biochem Genet 1988; 26 : 401–20). The doublet polypeptide chains of α-L-fucosidase in JH cultures may represent expression of two distinct allelic forms of mutant α-L-fucosidase.