Synaptosomal-associated Protein 25 (SNAP25), also known as SUP, is a key t-SNARE protein involved in vesicle exocytosis. SNAP25 is expressed in neurons, pancreatic beta cells, and adrenal chromaffin cells, and is one component of the trans-SNARE complex involved in vesicle docking and membrane fusion. SNAP25 is also thought to regulate plasma membrane recycling through its interaction with Centromere Protein F. In addition, SNAP25 can inhibit presynaptic calcium currents by interacting with P-, Q-, and L-type voltage-gated calcium channels, and can modulate the gating characteristics of the delayed rectifier voltage-dependent potassium channel KCNB1 in pancreatic beta cells. SNAP25 contains two t-SNARE coiled-coil homology domains at amino acids (aa) 19-81 and 140-202, and a proteolytic cleavage site at Arg180:Ile181. There are two splice variants, termed SNAP25A and SNAP25B, which only differ by 9 aa in the first t-SNARE coiled-coil homology domain. SNAP25B, the canonical sequence, is the major isoform in adult tissue while SNAP25A is mainly expressed in developing neural tissue. Human SNAP25B is 206 aa in length and has a predicted molecular weight of 24-29 kDa. Full-length human, mouse, and rat SNAP25B are identical in aa sequence.