The Journal of Cell Biology, Vol 102, 1264-1270, Copyright © 1986 by The Rockefeller University Press

ARTICLES

Lysosomal enzymes in Dictyostelium discoideum are transported to lysosomes at distinctly different rates

JA Cardelli, GS Golumbeski and RL Dimond

We are investigating the molecular mechanisms involved in the localization of lysosomal enzymes in Dictyostelium discoideum, an organism that lacks any detectable mannose-6-phosphate receptors. The lysosomal enzymes alpha-mannosidase and beta-glucosidase are both initially synthesized as precursor polypeptides that are proteolytically processed to mature forms and deposited in lysosomes. Time course experiments revealed that 20 min into the chase period, the pulse-labeled alpha-mannosidase precursor (140 kD) begins to be processed, and 35 min into the chase 50% of the polypeptides are cleaved to mature 60 and 58-kD forms. In contrast, the pulse-labeled beta-glucosidase precursor (105 kD) begins to be processed 10 min into the chase period, and by 30 min of the chase all of the precursor has been converted into mature 100-kD subunits. Between 5 and 10% of both precursors escape processing and are rapidly secreted from cells. Endoglycosidase H treatment of immunopurified radioactively labeled alpha-mannosidase and beta-glucosidase precursor polypeptides demonstrated that the beta-glucosidase precursor becomes resistant to enzyme digestion 10 min sooner than the alpha-mannosidase precursor. Moreover, subcellular fractionation studies have revealed that 70-75% of the pulse-labeled beta-glucosidase molecules move from the rough endoplasmic reticulum (RER) to the Golgi complex less than 10 min into the chase. In contrast, 20 min of chase are required before 50% of the pulse-labeled alpha-mannosidase precursor exits the RER. The beta- glucosidase and alpha-mannosidase precursor polypeptides are both membrane associated along the entire transport pathway. After proteolytic cleavage, the mature forms of both enzymes are released into the lumen of lysosomes. These results suggest that beta- glucosidase is transported from the RER to the Golgi complex and ultimately lysosomes at a distinctly faster rate than the alpha- mannosidase precursor. Thus, our results are consistent with the presence of a receptor that recognizes the beta-glucosidase precursor more readily than the alpha-mannosidase precursor and therefore more quickly directs these polypeptides to the Golgi complex.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

• Lefkir, Y., de Chassey, B., Dubois, A., Bogdanovic, A., Brady, R. J., Destaing, O., Bruckert, F., O'Halloran, T. J., Cosson, P., Letourneur, F. (2003). The AP-1 Clathrin-adaptor Is Required for Lysosomal Enzymes Sorting and Biogenesis of the Contractile Vacuole Complex in Dictyostelium Cells. Mol. Biol. Cell 14: 1835-1851 [Abstract] [Full Text]  
• Journet, A, Chapel, A, Jehan, S, Adessi, C, Freeze, H, Klein, G, Garin, J (1999). Characterization of Dictyostelium discoideum cathepsin D. J. Cell Sci. 112: 3833-3843 [Abstract]  
• Souza, G., Mehta, D., Lammertz, M, Rodriguez-Paris, J, Wu, R, Cardelli, J., Freeze, H. (1997). Dictyostelium lysosomal proteins with different sugar modifications sort to functionally distinct compartments. J. Cell Sci. 110: 2239-2248 [Abstract]  
• Mehta, D. P., Ichikawa, M., Salimath, P. V., Etchison, J. R., Haak, R., Manzi, A., Freeze, H. H. (1996). A Lysosomal Cysteine Proteinase from Dictyostelium discoideum Contains N-Acetylglucosamine-1-phosphate Bound to Serine but Not Mannose-6-phosphate on N-linked Oligosaccharides. J. Biol. Chem. 271: 10897-10903 [Abstract] [Full Text]  
• Temesvari, L. A., Bush, J. M., Peterson, M. D., Novak, K. D., Titus, M. A., Cardelli, J. A. (1996). Examination of the endosomal and lysosomal pathways in Dictyostelium discoideum myosin I mutants. J. Cell Sci. 109: 663-673 [Abstract]  
• Temesvari, L., Rodriguez-Paris, J., Bush, J., Zhang, L, Cardelli, J. (1996). Involvement of the vacuolar proton-translocating ATPase in multiple steps of the endo-lysosomal system and in the contractile vacuole system of Dictyostelium discoideum. J. Cell Sci. 109: 1479-1495 [Abstract]  
• Bush, J, Nolta, K, Rodriguez-Paris, J, Kaufmann, N, O'Halloran, T, Ruscetti, T, Temesvari, L, Steck, T, Cardelli, J (1994). A Rab4-like GTPase in Dictyostelium discoideum colocalizes with V-H(+)-ATPases in reticular membranes of the contractile vacuole complex and in lysosomes. J. Cell Sci. 107: 2801-2812 [Abstract]  

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents