The role of the cathepsin D propeptide in sorting to the lysosome

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Abstract

The propeptides of lysosomal enzymes have been implicated in membrane association and mannose 6-phosphate-independent sorting to the lysosome (Rijnboutt, S., Aerts, H., Geuze, H. J., Tager, J. M., and Strous, G. J. (1991) J. Biol. Chem. 266, 4862-4868; McIntyre, G. F., and Erickson, A. H. (1991) J. Biol. Chem. 266, 15438-15445). In this report, the function of the propeptide of procathepsin D in sorting to the lysosome was directly assessed using a cathepsin D deletion mutant lacking the propeptide, and using a chimeric cDNA encoding the cathepsin D propeptide fused to the secretory protein α-lactalbumin. Proteins encoded by these cDNAs were expressed in mouse Ltk- cells and in human hepatoma Hep G2 cells, and then immunoprecipitated and analyzed by SDS-polyacrylamide gel electrophoresis. The deletion mutant was glycosylated but was rapidly degraded in a chloroquine- independent fashion and did not assume an active conformation. Thus the propeptide appeared to be necessary for correct folding. The chimeric protein was glycosylated and secreted. The coincidence of complex oligosaccharide modification and secretion of the chimeric protein suggested that it was slowly released from the endoplasmic reticulum and rapidly passed through the cell to the extracellular compartment. This was confirmed by immunofluorescent localization of the proteins. The data indicated that the propeptide appeared to be necessary for folding of cathepsin D but, unlike the yeast vacuolar propeptides, was not sufficient to direct a secretory protein to the lysosome in fibroblasts or in epithelial cells.

Original languageEnglish
Pages (from-to)21738-21745
Number of pages8
JournalJournal of Biological Chemistry
Volume267
Issue number30
StatePublished - Oct 25 1992

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Cathepsin D
Lysosomes
Sorting
Proteins
Complementary DNA
Lactalbumin
Chloroquine
Hep G2 Cells
Fibroblasts
Electrophoresis
Oligosaccharides
Endoplasmic Reticulum
Yeast
Conformations
Polyacrylamide Gel Electrophoresis
Hepatocellular Carcinoma
Yeasts
Epithelial Cells
Association reactions
Membranes

ASJC Scopus subject areas

  • Biochemistry

Cite this

The role of the cathepsin D propeptide in sorting to the lysosome. / Conner, Gregory E.

In: Journal of Biological Chemistry, Vol. 267, No. 30, 25.10.1992, p. 21738-21745.

Research output: Contribution to journalArticle

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