SNAP-25 is a protein involved in regulated membrane fusion and part of the SNARE 
complex. It exists as two splicing variants, SNAP-25a and SNAP-25b, which differ 
in 9 out of 206 amino acids. SNAP-25 together with Syntaxin 1 and VAMP-2 forms 
the ternary SNARE complex essential for mediating activity-dependent release of 
hormones and neurotransmitters. The functional difference between SNAP-25a and 
SNAP-25b is poorly understood as both can participate in SNARE complexes and 
mediate membrane fusion. However, we recently demonstrated that 
SNAP-25b-deficiency results in metabolic disease and increased insulin 
secretion. Here we investigated if SNAP-25a and SNAP-25b differently affect 
interactions with other SNAREs and SNARE-interacting proteins in mouse 
hippocampus. Adult mice almost exclusively express the SNAP-25b protein in 
hippocampus whereas SNAP-25b-deficient mice only express SNAP-25a. 
Immunoprecipitation studies showed no significant differences in amount of 
Syntaxin 1 and VAMP-2 co-precipitated with the different SNAP-25 isoforms. In 
contrast, Munc18-1, that preferentially interacts with SNAP-25 via Syntaxin 1 
and/or the trimeric SNARE complex, demonstrated an increased ability to bind 
protein-complexes containing SNAP-25b. Moreover, we found that both SNAP-25 
isoforms co-precipitated the Gβγ subunits of the heterotrimeric G proteins, an 
interaction known to play a role in presynaptic inhibition. We have identified 
Gβ1 and Gβ2 as the interacting partners of both SNAP-25 isoforms in mouse 
hippocampus, but Gβ2 was less efficiently captured by SNAP-25a. These results 
implicate that the two SNAP-25 isoforms could differently mediate protein 
interactions outside the ternary SNARE core complex and thereby contribute to 
modulate neurotransmission.