A conformationally altered precursor to the lysosomal enzyme alpha-mannosidase accumulates in the endoplasmic reticulum in a mutant strain of Dictyostelium discoideum

• Published in: The Journal of biological chemistry Vol. 261; no. 21; pp. 9595 - 9602
• Main Authors: Woychik, N A, Cardelli, J A, Dimond, R L
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25-07-1986; American Society for Biochemistry and Molecular Biology
• Subjects: Acetylglucosaminidase - metabolism; ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; alpha-Mannosidase; Biological and medical sciences; Cell physiology; CHAMPIGNON; CITOPLASMA; CYTOPLASM; CYTOPLASME; Dictyostelium - enzymology; Dictyostelium - genetics; Electrophoresis, Polyacrylamide Gel; ENDOPLASMIC RETICULUM; Endoplasmic Reticulum - enzymology; Enzyme Precursors - analysis; ENZYMIC ACTIVITY; Fundamental and applied biological sciences. Psychology; FUNGI; GLICOSIDASAS; GLYCOSIDASE; GLYCOSIDASES; Lysosomes - enzymology; Mannosidases - analysis; Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; Membrane and intracellular transports; Molecular and cellular biology; MUTANT; MUTANTES; MUTANTS; Mutation; Protein Conformation; RETICULO ENDOPLASMATICO; RETICULUM ENDOPLASMIQUE; Sulfates - metabolism; Dictyostelium discoideum; Protozoa; Intracellular transport; Enzyme; Lysosome; Biosynthesis; Mutation; Endoplasmic reticulum; Accumulation; α-D-Mannosidase; Mycetozoa; Conformation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)67555-6

The mutant strain of Dictyostelium discoideum, HMW-437, contains a mutation in the structural gene coding for the lysosomal enzyme alpha-mannosidase. Unlike the wild type strain, Ax3, this strain fails to proteolytically process or secrete the 140,000-dalton alpha-mannosidase precursor. The level of sulfate incorporation into the mutant precursor was significantly lower when compared to the wild type precursor. In addition, the mutant precursor was entirely sensitive to endoglycosidase H. Subcellular fractionation of HMW-437 membranes indicated that the majority of the alpha-mannosidase precursor sedimented in a region of the gradient corresponding to the rough endoplasmic reticulum. This accumulation within the rough endoplasmic reticulum did not appear to result from gross conformational changes which lead to aggregation. Trypsin digestion of radioactively labeled Ax3 and HMW-437 precursors demonstrated that there were differences in susceptibility to protease cleavage between the wild type and mutant alpha-mannosidase precursor molecules, suggesting that a minor conformational change could contribute to the accumulation of the mutant precursor inside the endoplasmic reticulum.