Biogenesis of lysosomal enzymes in the α-glucosidase II-deficient modA mutant of Dictyostelium discoideum: Retention of α-1,3-linked glucose on N-linked oligosaccharides delays intracellular transport but does not alter sorting of α-mannosidase or β-glucosidase

• Published in: Archives of biochemistry and biophysics Vol. 273; no. 2; pp. 479 - 490
• Main Authors: Ebert, David L., Bush, John M., Dimond, Randall L., Cardelli, James A.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.09.1989; Elsevier
• Subjects: alpha-Glucosidases - deficiency; alpha-Glucosidases - genetics; Analytical, structural and metabolic biochemistry; beta-Glucosidase - biosynthesis; beta-Glucosidase - metabolism; Biological and medical sciences; Biological Transport; Dictyostelium - enzymology; Dictyostelium - genetics; Dictyostelium discoideum; Electrophoresis, Polyacrylamide Gel; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glucose - metabolism; Hydrolases; Hydrolysis; Kinetics; lysosomes; Lysosomes - enzymology; Mannosidases - biosynthesis; Mannosidases - metabolism; Mutation; Oligosaccharides - metabolism; Protein Conformation; Protozoa; Gel electrophoresis; Enzyme; Deficiency; Oligosaccharide; Lysosome; Glucose; α-D»-Mannosidase; Dictyostelium discoideum; Immunoprecipitation reaction; Microorganism culture; Enzymatic digestion; Carbohydrate; β-D»-Glucosidase; Mutation; Endoplasmic reticulum; Mycetozoa; α-D-Glucosidase
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(89)90507-9

The endoplasmic reticulum-localized enzyme α-glucosidase II is responsible for removing the two α-1,3-linked glucose residues from N-linked oligosaccharides of glycoproteins. This activity is missing in the modA mutant strain, M31, of Dictyostelium discoideum. Results from both radiolabeled pulse-chase and subcellular fractionation experiments indicate that this deficiency did not prevent intracellular transport and proteolytic processing of the lysosomal enzymes, α-mannosidase and β-glucosidase. However, the rate at which the glucosylated precursors left the rough endoplasmic reticulum was several-fold slower than the rate at which the wild-type precursors left this compartment. Retention of glucose residues did not disrupt the binding of the precursor forms of the enzymes with intracellular membranes, indicating that the delay in movement of proteins from the ER did not result from lack of association with membranes. However, the mutant α-mannosidase precursor contained more trypsin-sensitive sites than did the wild-type precursor, suggesting that improper folding of precursor molecules might account for the slow rate of transport to the Golgi complex. Percoll density gradient fractionation of extracts prepared from M31 cells indicated that the proteolytically processed mature forms of α-mannosidase and β-glucosidase were localized to lysosomes. Finally, the mutation in M31 may have other, more dramatic, effects on the lysosomal system since two enzymes, N-acetylglucosaminidase and acid phosphatase, were secreted much less efficiently from lysosomal compartments by the mutant strain.