A PEPTIDE THAT MIMICS THE CARBOXY-TERMINAL DOMAIN OF SNAP-25 BLOCKS CA2-DEPENDENT EXOCYTOSIS IN CHROMAFFIN CELLS()

SNAP-25, a synaptosomal associated membrane protein of 25 kDa, partici pates in the presynaptic process of vesicle-plasma membrane fusion tha t results in neurotransmitter release at central nervous system synaps es, SNAP-25 occurs in neuroendocrine cells and, in analogy to its role in neurons, has been implicated in catecholamine secretion, yet the n ature of the underlying mechanism remains obscure, Here me use an anti -SNAP-25 monoclonal antibody to show that SNAP-25 is localized at the cytosolic surface of the plasma membrane of chromaffin cells, This ant ibody inhibited the Ca2+-evoked catecholamine release from digitonin-p ermeabilized chromaffin cells in a time- and dose-dependent manner, Re markably, a 20-mer synthetic peptide representing the sequence of the C-terminal domain of SNAP-25 blocked Ca2+-dependent catecholamine rele ase with an IC50 = 20 mu M. The inhibitory activity of the peptide was sequence-specific as evidenced by the inertness of a control peptide with the same amino acid composition but random order, The C-terminal segment of SNAP-25, therefore, plays a key role in regulating Ca2+-dep endent exocytosis, presumably mediated via interactions with other pro tein components of the fusion complex.