A PEPTIDE THAT MIMICS THE C-TERMINAL SEQUENCE OF SNAP-25 INHIBITS SECRETORY VESICLE DOCKING IN CHROMAFFIN CELLS

Excitation-secretion uncoupling peptides (ESUPs) are inhibitors of Ca2 +-dependent exocytosis in neural and endocrine cells. Their mechanism of action, however, remains elusive. We report that ESUP-A, a 20-mer p eptide patterned after the C terminus of SNAP-25 (synaptosomal associa ted protein of 25 kDa) and containing the cleavage sequence for botuli num neurotoxin A (BoNT A), abrogates the slow, ATP-dependent component of the exocytotic pathway, without affecting the fast, ATP-independen t, Ca2+-mediated fusion event. Ultrastructural analysis indicates that ESUP-A induces a drastic accumulation of dense-core vesicles near the plasma membrane, mimicking the effect of BoNT A. Together, these find ings argue in favor of the notion that ESUP-A inhibits ATP-primed exoc ytosis by blocking vesicle docking. Identification of blocking peptide s which mimic sequences that bind to complementary partner domains on interacting proteins of the exocytotic machinery provides new pharmaco logical tools to dissect the molecular and mechanistic details of neur o secretion. Our findings may assist in developing ESUPs as substitute drugs to BoNTs for the treatment of spasmodic disorders.