Title : Sorting of non-glycosylated human
procathepsin S in mammalian cells
Abstract :
- Cathepsin S , a lysosomal cysteine protease , is synthesized as inactive precursor
- It is activated in the lysosomes by a proteolytic cleavage of the propeptide
- 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
- The cells expressed glycosylated and non-glycosylated procathepsin S , respectively
- Large amounts of the precursors were secreted into the culture media by both transfectants
- Secreted wild type procathepsin S contained Man-6-phosphate in the oligosaccharide chain.
- Wild type procathepsin S was activated in the cells but no maturation occurred in the culture media
- 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
- A reuptake of the glycosylated and non-glycosylated procathepsin S by HEK 293-cells could be observed
- Small amounts of mature cathepsin S were detected in the lysosomes of the mutant transfectants
- Subcellular fractionation showed non-glycosylated procathepsin S in the membrane fraction
- 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.