One point mutation which converts glycine-317 to aspartate of tissue-nonspecific alkaline phosphatase (TNSALP) was reported to be associated with lethal hypophosphatasia. In order to define the molecular defect of TNSALP underlying the pathogenesis of hypophosphatasia, we have examined the biosynthesis of TNSALP with a Gly317→Asp substitution. When expressed in COS-1 cells, the mutant did not exhibit alkaline phosphatase activity at all, indicating that the replacement of glycine-317 with aspartate abolishes the catalytic activity of TNSALP. Pulse-chase experiments showed that the newly synthesized mutant failed to acquire Endo H-resistance and to reach the cell surface. Interestingly, this TNSALP mutant was found to form a disulfide-bonded high-molecular-mass aggregate and was rapidly degraded within the cell, though the mutant protein was modified by glycosylphosphatidylinositol (GPI). Lactacystin, an inhibitor of the proteasome, obstructed the degradation of the mutant protein, suggesting the involvement of proteasome as a part of quality control of TNSALP.
|Original language||English (US)|
|Number of pages||6|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - May 29 1998|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology