J. Biol. Chem., Vol. 262, Issue 21, 10008-10014, 07, 1987
A single mutation prevents the normal intracellular transport of multiple lysosomal proteins from the rough endoplasmic reticulum
NA Woychik and RL Dimond
Dictyostelium discoideum strain HMW-426 has been previously shown to be
defective in the proteolytic processing of the lysosomal enzyme precursor
to alpha-mannosidase. We have now shown that the mutant is defective in the
proteolytic processing of a second lysosomal enzyme, beta-glucosidase.
Digestion of the HMW-426 alpha-mannosidase and beta- glucosidase precursors
with endoglycosidase H revealed that the majority of oligosaccharide side
chains on both precursors were sensitive to cleavage by this enzyme,
indicating that both precursors fail to reach the Golgi apparatus.
Subcellular fractionation experiments demonstrated that these two mutant
precursors accumulated inside the lumen of the rough endoplasmic reticulum.
The alpha- mannosidase precursor is conformationally altered, as evidenced
by its abnormal protease susceptibility, suggesting that altered
conformation is responsible for a generalized defect in transport of
lysosomal protein precursors from the rough endoplasmic reticulum in the
mutant.