title: Mannose 6-phosphate-independent targeting of lysosomal enzymes in I-cell disease B lymphoblasts.
abstract: B lymphocytes from patients with I-cell disease (ICD) maintain normal cellular levels of lysosomal enzymes despite a deficiency of the enzyme UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. We find that an ICD B lymphoblastoid cell line targets about 45% of the lysosomal protease cathepsin D to dense lysosomes. This targeting occurs in the absence of detectable mannose 6-phosphate residues on the cathepsin D and is not observed in ICD fibroblasts. The secretory protein pepsinogen, which is closely related to cathepsin D in both amino acid sequence and three-dimensional structure, is mostly excluded from dense lysosomes, indicating that the lymphoblast targeting pathway is specific. Carbohydrate residues are not required for lysosomal targeting, since a non-glycosylated mutant cathepsin D is sorted with comparable efficiency to the wild type protein. Analysis of a number of cathepsin D/pepsinogen chimeric proteins indicates that an extensive polypeptide determinant in the cathepsin D carboxyl lobe can confer efficient lysosomal sorting when introduced into the pepsinogen sequence. This determinant overlaps but is not identical to the recognition marker for phosphotransferase. These results indicate that a specific protein recognition event underlies Man-6-P-independent lysosomal sorting in ICD lymphoblasts.
authors.affiliation: Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: J N
authors.initials: JN
authors.lastname: Glickman
authors.forename: S
authors.initials: S
authors.lastname: Kornfeld
mesh_terms: D001402:B-Lymphocytes / Q000201:enzymology / Q000378:metabolism*; D001692:Biological Transport; D015415:Biomarkers; D002402:Cathepsin D / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation; D002460:Cell Line; D004252:DNA Mutational Analysis; D006023:Glycoproteins / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000201:enzymology / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism*; D009081:Mucolipidoses / Q000201:enzymology / Q000378:metabolism*; D010435:Pepsinogens / Q000235:genetics / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D015415:Biomarkers; D006023:Glycoproteins; D008360:Mannosephosphates; D010435:Pepsinogens; D011993:Recombinant Fusion Proteins; C027693:mannose-6-phosphate; D010770:Phosphotransferases; D002402:Cathepsin D