Glycobiology vol 1 no 6 pp. 595-604, 1991
© 1991
research-article |
Biosynthesis, processing, and secretion of 
-L-fucosidase in lymphoid cells from patients with I-cell disease and pseudo-Hurler polydystrophy
1Department of Gynecologic Oncology, Roswell Park Cancer Institute Buffalo, NY 14263, USA
2Department of Neurosciences, M-024, University of California, San Diego School of Medicine La Jolla, CA 92093, USA
Received on April 1, 1991; accepted on July 17, 1991
N-Acetylglucosamine 1-phosphotransferase is a key enzyme required for synthesis of the mannose 6-phosphate recognition marker that is used by many newly made acid hydrolases for their transport to lysosomes. It has previously been found that lymphoid cells from patients with I-cell disease and pseudo-Hurler polydystrophy have nearly normal intracellular and intralysosomal activities of several lysosomal acid hydrolases, despite a deficiency of N-acetylglucosamine 1-phosphotransferase. These results suggest that lymphoid cells may provide an important system to investigate alternate mechanisms for targeting newly made acid hydrolases to lysosomes. In the present study, the biosynthesis, processing and secretion of 
-L-fucosidase in I-cell and pseudoHurler lymphoid cells was used as a model system to study the existence of such mechanisms. The level of intracellular -L-fucosidase protein in exponentially growing I-cell or pseudo-Hurler lymphoid cultures was statistically indistinguishable from the mean of 19 control cultures. A 1.5 h [35S]methionine pulse experiment showed that -L-fucosidase is initially sythesized by I-cell, pseudo-Hurler and control cultures as an intracellular form (Mr = 58 000). Companion cultures chased with methionine from 2 to 21 h processed the enzyme to an intracellular form (Mr = 60 000) and an extracellular form (Mr = 62 000). All enzyme forms were glycoproteins with polypeptide chains of Mr 52 000. In control cells incubated with radioactive inorganic phosphate (32Pi), <1% of the 32Pi incorporated into -L-fucosidase was associated with carbohydrate chains and >99% with polypeptide chains. In I-cell disease lymphoid cells, the 32Pi incorporated into -L-fucosidase was associated solely with polypeptide chains. A qualitative analysis of phosphorylated residues identified phosphoserine in -L-fucosidase from control and I-cell lymphoid cells. Only -L-fucosidase from control cells contained mannose 6-phosphate. These results are consistent with the proposal that I-cell lymphoid cells may use a mannose 6-phosphate-independent mechanism for routing -L-fucosidase. Additional metabolic labelling experiments demonstrated the presence of 32P-labelled -L-fucosidase in both cells and medium of a control lymphoid culture, but only in cells of an I-cell lymphoid culture. In contrast, -L-fucosidase labelled with [35S]methionine was found in cells and medium of control and I-cell lymphoid cultures. Since phosphoserine was only found to occur in intracellular, but not in extracellular -L-fucosidase of the I-cell culture, we speculate that phosphoserine may be involved in intracellular retention of -L-fucosidase in I-cell lymphoid cells.
-L-fucosidase
I-cell disease
lymphoid cells
phos-phorylation
pseudo-Hurler polydystrophy
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