Calpastatin (the Endogenous Calpain Inhibitor) and Membrane Protein Degradation in Cell Fusion

Cell membrane fusion is a ubiquitous cellular process, mediating such phenomena as fertilization, muscle development, certain viral infections, and giant cell formation from macrophages. For membrane fusion to occur, the cell membranes must attach to each other, usually by means of interactions between membrane receptors. Increased cellular Ca²⁺ is required for the various fusion events, and changes occur in the cell membrane and cytoskeleton. Fusion of membranes occurs between the two phospholipid bilayers in regions that are poor in proteins (fusion-potent domains). It has been proposed that membrane protein degradation contributes to the disorganization of cell membrane and cytoskeleton in preparation for the fusion of the cell membranes (1 –3 ).