Site-specific calcium-dependent proteolysis of neuronal protein GAP-43.

GAP-43 is a presynaptic protein participating in signal transduction processes in nerve terminals. GAP-43 exists in neurons along with two truncated forms devoid of 4 and 40 N-terminal residues. In this report, we show that these forms of GAP-43 are proteolytic fragments derived from calcium-dependent cleavage of GAP-43 molecule at 5th and 41st residues. GAP-43 site-specific proteolysis in synaptosome and cytosol fractions proved to be dependent on the addition of millimolar amounts of calcium. This fact together with inhibition of GAP-43 proteolysis by calpain inhibitors as well as local composition of the cleavage sites indicates to the participation of calpain in this process. The proteolysis disturbs some properties characteristic for whole GAP-43 molecules, in particular, calmodulin binding and Ser-41 phosphorylation, when the cleavage occurs at 41st residue. Some other GAP-43 properties (G(o) protein activation and membrane attachment) are retained by separate fragments. Therefore, calcium controlled site-specific proteolysis of GAP-43 can be of great physiological significance.