Complexin II regulates degranulation in RBL-2H3 cells by interacting with SNARE complex containing syntaxin-3

Recent studies have revealed that SNARE proteins are involved in the exocytotic release (degranulation) in mast cells. However, the roles of SNARE regulatory proteins are poorly understood. Complexin is one such regulatory protein and it plays a crucial role in exocytotic release. In this study, we characterized the interaction between SNARE complex and complexin II in mast cells by GST pull-down assay and in vitro binding assay. We found that the SNARE complex that interacted with complexin II consisted of syntaxin-3, SNAP-23, and VAMP-2 or -8, whereas syntaxin-4 was not detected. Recombinant syntaxin-3 binds to complexin II by itself, but its affinity to complexin II was enhanced upon addition of VAMP-8 and SNAP-23. Furthermore, the region of complexin II responsible for binding to the SNARE complex, was near the central α-helix region. These results suggest that complexin II regulates degranulation by interacting with the SNARE complex containing syntaxin-3.