Calcium-dependent proteases: an enzyme system active at cellular membranes?
Proteases having a neutral pH optimum and an absolute requirement for calcium ion are found in virtually all mammalian cells. Association of calcium-dependent proteases and a specific inhibitor protein with biological membranes seems to be an important regulatory feature of this proteolytic system, and it is likely that membranes are preferred sites for calcium-dependent protease action. Several recent hypotheses for the physiological function of calcium-dependent proteolysis are consistent with a membrane-associated protease action. Calcium-dependent proteases may participate in cell membrane fusion: the proteolysis of membrane proteins, which is required for the efficient fusion of erythrocytes, may be catalyzed by these enzymes. There is also evidence for the involvement of calcium-dependent proteolysis in postsynaptic membrane remodeling in the hippocampus after long-term potentiation. Although the relationship of the proteolysis to synaptic function is not known, it could have important physiological or pathophysiological consequences. Finally, it has recently been suggested that calcium-dependent proteolysis may be a physiologically significant mechanism for activating membrane-associated protein kinase C after exposure of some cell types to phorbol esters or other mitogens. Further pursuit of these hypotheses may reveal a novel role for intracellular calcium-regulated proteolysis in membrane-associated cell functions.
D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000502:physiology*; D002459:Cell Fusion; D004789:Enzyme Activation; D005971:Glutamates / Q000633:toxicity; D018698:Glutamic Acid; D007527:Isoenzymes / Q000502:physiology; D008565:Membrane Proteins / Q000502:physiology*; D008568:Memory / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism
D005971:Glutamates; D007527:Isoenzymes; D008565:Membrane Proteins; D018698:Glutamic Acid; D011493:Protein Kinase C; D002154:Calpain; D002118:Calcium