Dictyostelium lysosomal proteins with different sugar modifications sort to functionally distinct compartments.
Many Dictyostelium lysosomal enzymes contain mannose-6-phosphate (Man-6-P) in their N-linked oligosaccharide chains. We have now characterized a new group of lysosomal proteins that contain N-acetylglucosamine-1-phosphate (GlcNAc-1-P) linked to serine residues. GlcNAc-1-P-containing proteins, which include papain-like cysteine proteinases, cofractionate with the lysosomal markers and are in functional vesicles of the endosomal/lysosomal pathway. Immunoblots probed with reagents specific for each carbohydrate modification indicate that the lysosomal proteins are modified either by Man-6-P or GlcNAc-1-P, but not by both. Confocal microscopy shows that the two sets of proteins reside in physically and functionally distinct compartments. Vesicles with GlcNAc-1-P fuse with nascent bacteria-loaded phagosomes less than 3 minutes after ingestion, while those with Man-6-P do not participate in bacterial digestion until about 15 minutes after phagocytosis. Even though both types of vesicles fuse with phagosomes, GlcNAc-1-P- and Man-6-P-bearing proteins rarely colocalize. Since both lysosomal enzymes and their bound carbohydrate modifications are stable in lysosomes, a targeting or retrieval mechanism based on these carbohydrate modifications probably establishes and/or maintains segregation.
Souza
G M
GM
The Burnham Institute, La Jolla Research Center, La Jolla, CA 92037, USA.
Mehta
D P
DP
Lammertz
M
M
Rodriguez-Paris
J
J
Wu
R
R
Cardelli
J A
JA
Freeze
H H
HH
D000117:Acetylglucosamine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D000818:Animals; D001419:Bacteria / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D002451:Cell Compartmentation / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004023:Dictyostelium / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011992:Endosomes / Q000737:chemistry / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D006867:Hydrolases / Q000378:metabolism; D007425:Intracellular Membranes / Q000737:chemistry / Q000201:enzymology; D008247:Lysosomes / Q000737:chemistry / Q000201:enzymology*; D008360:Mannosephosphates / Q000032:analysis / Q000378:metabolism*; D010587:Phagocytosis / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology; D015800:Protozoan Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000737:chemistry
D005656:Fungal Proteins; D006023:Glycoproteins; D008360:Mannosephosphates; D010750:Phosphoproteins; D015800:Protozoan Proteins; C027693:mannose-6-phosphate; C026146:N-acetylglucosamine-1-phosphate; D006867:Hydrolases; D003546:Cysteine Endopeptidases; D000117:Acetylglucosamine