PMID: 9524075

 

    Legend: Sugar

Title : Sorting of non-glycosylated human procathepsin S in mammalian cells

Abstract :
  1. Cathepsin S , a lysosomal cysteine protease , is synthesized as inactive precursor
  2. It is activated in the lysosomes by a proteolytic cleavage of the propeptide
  3. HEK 293-cells which do not express cathepsin S were transfected with cDNA of either wild type human procathepsin S or a mutant procathepsin S in which Asn of the only glycosylation site in the proregion was replaced by Gln
  4. The cells expressed glycosylated and non-glycosylated procathepsin S , respectively
  5. Large amounts of the precursors were secreted into the culture media by both transfectants
  6. Secreted wild type procathepsin S contained Man-6-phosphate in the oligosaccharide chain.
  7. Wild type procathepsin S was activated in the cells but no maturation occurred in the culture media
  8. In vitro processing of glycosylated as well as of non-glycosylated procathepsin S gave fully active enzymes thus indicating that the oligosaccharide chain was not necessary for proper folding
  9. A reuptake of the glycosylated and non-glycosylated procathepsin S by HEK 293-cells could be observed
  10. Small amounts of mature cathepsin S were detected in the lysosomes of the mutant transfectants
  11. Subcellular fractionation showed non-glycosylated procathepsin S in the membrane fraction
  12. Non-glycosylated procathepsin S was bound to the plasma membrane at 2 degrees C, suggesting an additional sorting motif in the cathepsin S molecule besides the Man-6-phosphate residue.