Lack of proteolytic processing of α‐L‐fucosidase in human skin fibroblasts

Abstract

Acid hydrolases are synthesized as precursors that undergo several posttranslational modifications including proteolytic processing to a smaller mature enzyme. The amount of proteolytic processing varies for different acid hydrolases, and many details of the intracellular pathways are not known. The processing of alpha-L-fucosidase was distinguished from that of other acid hydrolases reported when studied in systematic pulse-chase labeling experiments. Only one form of alpha-L-fucosidase, Mr 56,000-57,000, was demonstrated intra- and extracellularly. Under the same conditions, N-acetyl-beta-D-glucosaminidase was shown to be processed with several forms, as previously reported by Hasilik and Neufeld (1980a). To obtain these results, human skin fibroblasts were labeled metabolically with L-[3H]leucine for periods of 20 min to 8 hr with varying periods of chase from 1 to 96 hr with nonradioactive L-leucine. alpha-L-Fucosidase was immunoprecipitated by a polyclonal antibody from material extracted from cells and ammonium sulfate precipitated medium and was examined by polyacrylamide gel electrophoresis under denaturing conditions. N-Acetyl-beta-D-glucosaminidase was examined with similar procedures and served as a control for the methods. Tunicamycin treatment of the cells was used to show that glycosylation did not obscure proteolytic processing because, again, only one form of the intra- and extracellular enzyme was observed, although of smaller size, Mr 52,000-53,000. In addition, separation of the cells into prelysosomal and lysosomal fractions showed only one form of the enzyme. It is concluded that alpha-L-fucosidase does not undergo proteolytic processing in human skin fibroblasts in the usual manner described for other acid hydrolases.

Isolation and sequence analysis of a cDNA encoding rat liver α-l-fucosidase

“…The lack of an obvious pro-segment larger than these one to five amino acid residues in the deduced amino acid sequence from rat liver a-L-fucosidase clone FC9 would argue against the existence of a major precursor form of the protein. Two recent studies examining the processing of a-L-fucosidase, one in human skin fibroblasts [32] and the other in human lymphocytes [33], reported no evidence for post-translational proteolysis of a precursor form of the enzyme. In both studies only a single polypeptide species having an Mr of approx.…”