Positive regulation of mu-calpain action by polyphosphoinositides.
Whether calcium is the only major intracellular activator of calpain has not yet been established. Here we demonstrate that polyphosphoinositides may play critical roles in the activation process of mu-calpain. Experiments with purified enzyme, substrate (fodrin), and phospholipids show that only polyphosphoinositides but not other lipids significantly promote calpain action in the physiological intracellular calcium range of 10(-7) to 10(-6) M. The effect of polyphosphoinositide is exerted through both a reduction in the calcium concentration required for calpain autolysis and an increase in the Vmax of the proteolytic reaction. Neomycin, a polyphosphoinositide-binding antibiotic, inhibits both polyphosphoinositide-assisted proteolysis in test tubes and calcium-induced calpain activation coupled with substrate proteolysis in intact cells. This implies that the presence of polyphosphoinositides may actually be a prerequisite for calpain activation inside cells.
Saido
T C
TC
Department of Molecular Biology, Tokyo Metropolitan Institute of Medical Science, Japan.
Shibata
M
M
Takenawa
T
T
Murofushi
H
H
Suzuki
K
K
D000595:Amino Acid Sequence; D000906:Antibodies; D002118:Calcium / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D015458:Leukemia, T-Cell; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D009355:Neomycin / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000494:pharmacology*; D010743:Phospholipids / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D013049:Spectrin
D000906:Antibodies; D002118:Calcium; D002154:Calpain; D002352:Carrier Proteins; D007527:Isoenzymes; D046911:Macromolecular Substances; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009355:Neomycin; D010455:Peptides; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D013049:Spectrin