Effect of Complexin II on Membrane Fusion between Liposomes Containing Mast Cell SNARE Proteins

Mast cells are involved in allergic responses and undergo exocytotic release of inflammatory mediators in response to antigen stimulation. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are involved in this membrane fusion process; some SNARE-binding proteins regulate SNARE-dependent liposome membrane fusion. SNARE-binding protein complexin II is expressed in mast cells, where it positively regulates exocytotic release after antigen stimulation. We found that complexin II suppressed SNARE-dependent membrane fusion between mast cell SNARE-containing liposomes. This inhibitory effect of complexin II was abolished when we used a structurally divergent mutant (R59H) complexin II, where Arg59 is substituted with histidine. These results suggest that complexin II negatively regulates SNARE-dependent exocytotic membrane fusion in mast cells, and this inhibitory effect is dependent upon Arg59.