Gm. Souza et al., DICTYOSTELIUM LYSOSOMAL PROTEINS WITH DIFFERENT SUGAR MODIFICATIONS SORT TO FUNCTIONALLY DISTINCT COMPARTMENTS, Journal of Cell Science, 110, 1997, pp. 2239-2248
Many Dictyostelium lysosomal enzymes contain mannose-6-phosphate (Man-
6-P) in their N-linked oligosaccharide chains. We have now characteriz
ed a new group of lysosomal proteins that contain N-acetylglucosamine-
1-phosphate (GlcNAc-1-P) linked to serine residues. GlcNAc-1-P-contain
ing proteins, which include papain-like cysteine proteinases, cofracti
onate with the lysosomal markers and are in functional vesicles of the
endosomal/lysosomal pathway, Immunoblots probed with reagents specifi
c for each carbohydrate modification indicate that the lysosomal prote
ins are modified either by Man-6-P or GlcNAc-1-P, but not by both, Con
focal microscopy shows that the two sets of proteins reside in physica
lly and functionally distinct compartments, Vesicles with GlcNAc-1-P f
use with nascent bacteria-loaded phagosomes less than 3 minutes after
ingestion, while those with Man-6-P do not participate in bacterial di
gestion until about 15 minutes after phagocytosis, Even though both ty
pes of vesicles fuse with phagosomes, GlcNAc-1-P- and Man-6-P-bearing
proteins rarely colocalize, Since both lysosomal enzymes and their bou
nd carbohydrate modifications are stable in lysosomes, a targeting or
retrieval mechanism based on these carbohydrate modifications probably
establishes and/or maintains segregation.