A gain-of-function mutant of Munc18-1 stimulates secretory granule recruitment and exocytosis and reveals a direct interaction of Munc18-1 with Rab3

Margaret E Graham , Mark Tw Handley , Jeff W Barclay , Leo F Ciufo , Stephanie L Barrow , Alan Morgan , Robert D Burgoyne (1)

1 The Physiological Laboratory

Munc18-1 plays a crucial role in regulated exocytosis in neurons and neuroendocrine cells through effects on vesicle docking and membrane fusion. The molecular basis for Munc18 function is still unclear as are the links with Rabs and SNARE (soluble NSF-attachment protein receptors) proteins that are also required. Munc18-1 can bind to the SNAREs through at least three modes of interaction, including binding to the closed conformation of syntaxin 1. Using a gain of function mutation in Munc18-1 (E466K), based on a mutation in the related yeast Sly1p protein, we have identified a direct interaction of Munc18-1 with Rab3A which is increased by the mutation. Expression of Munc18-1 with the E466K mutation increases exocytosis in adrenal chromaffin and PC12 cells and was found to increase the density of secretory granules at the periphery of PC12 cells suggesting a stimulatory effect on granule recruitment through docking or tethering. Both the increase in exocytosis and changes in granule distribution appears to require Munc18-1 E466K binding to the closed form of syntaxin 1 suggesting a role for this interaction in bridging Rab- and SNARE-mediated events in exocytosis.

Mots clés: Life Sciences

Margaret E Graham, Mark Tw Handley, Jeff W Barclay, Leo F Ciufo, Stephanie L Barrow, et al.. A gain-of-function mutant of Munc18-1 stimulates secretory granule recruitment and exocytosis and reveals a direct interaction of Munc18-1 with Rab3. Biochemical Journal, 2007, 409 (2), pp.407-416. ⟨10.1042/BJ20071094⟩. ⟨hal-00478869⟩