Direct interaction between SNAP-23 and L-type Ca²⁺channel

Abstract

Atomic force microscopy (AFM) in combination with electron microscopy (EM) and biochemical approaches, has helped in the discovery of the fusion pore or porosome at the cell plasma membrane, where secretory vesicles dock and fuse to release their contents [1][2][3][4][5][6][7]. The structure of the porosome in both exocrine [1,2,5,6], neuroendocrine cells [3,4], and in neurons [7], at nanometer-subnanometer resolution, and its dynamics in real time, have been determined. Immunochemical studies further demonstrate that t-SNAREs, NSF, actin, vimentin, α-fodrin and the calcium channels α1c and β 3, are part of the fusion pore complex [5,6]. The localization and possible arrangement of SNAREs at the fusion pore, was demonstrated from combined AFM, immunoAFM and electrophysiological measurements. Our studies reveal that the fusion pore or porosome is a cup-shaped lipoprotein structure, the base of which has tSNAREs and allows for docking and fusion of secretory vesicles, and the release of secretory products.Calcium influx through voltage-gated Ca 2+ -channels (VGCC's) has been implicated in triggering fusion of secretory vesicle membranes at the cell plasma membrane [8] AbstractDuring secretion, membrane-bound secretory vesicles dock and fuse at the base of porosomes in the cell plasma membrane. Among other proteins, the porosome is composed of SNAREs and Ca 2+ -channels. Ca 2+ -channels and SNAREs have been implicated in cell secretion. Several immunoprecipitation and binding studies suggest the physical interaction of the t-SNARE proteins, Syntaxin-1 and SNAP-25 with various Ca 2+ -channels. In this study, using yeast two-hybrid and immunoanalysis, we demonstrate for the first time, direct interaction of SNAP-23 and a L-type Ca 2+ -channel at the plasma membrane in pancreas.

Membrane fusion in cells: molecular machinery and mechanisms

“…This prompt mobilization of Ca 2+ is essential for many physiological functions, such as the release of neurotransmitters. Not surprisingly, calcium ion channels have been found in direct association with t-SNARE (SNAP-23), at the base of fusion pores or porosomes (permanent supramolecular structures at the cell plasma membrane [12][13][14][15][16][17][18][19]), where secretory vesicles dock and fuse to release their contents [20]. Calcium ion [Ca 2+ ] exists in its hydrated state within cells [11].…”

Morphine Prevents Lipopolysaccharide-Induced TNF Secretion in Mast Cells Blocking IκB Kinase Activation and SNAP-23 Phosphorylation: Correlation with the Formation of a β-Arrestin/TRAF6 Complex

“…Exocytosis of preformed mediators in MCs after FcεRI activation has been described to require the phosphorylation of Ser 120 and Ser 95 of SNAP-23 (43), and it has been shown that all the SNAP-23 bound to syntaxin 4 in the plasma membrane during exocytosis in RBL2H3 cells is phosphorylated (43). Interestingly, evidence indicates that SNAP-23 mediates the docking of secretory granules at low Ca 2+ levels (100 nM) by interacting with different members of the synaptotagmin family (44) and that SNAP-23 can associate with L-type Ca 2+ channels (45). Further analysis on the participation of SNAP-23 on secretion of preformed mediators in MC stimulated with different ligands will shed light on the mechanism behind rapid exocytosis of mediators in the absence of massive Ca 2+ mobilization or degranulation in MCs.…”

Functional Organization of the Porosome Complex and Associated Structures Facilitating Cellular Secretion

“…Porosome size ranges from 100 to 180 nm in pancreatic acinar cells to ~12 to 17 nm in neurons and astrocytes. Several proteins constitute the porosome complex (51), including structural proteins such as actin, ion channels such as the chloride and calcium channels (51,18), and the t-SNARE membrane fusion proteins located at its base (60), where secretory vesicles transiently dock and fuse to expel their contents. During cell secretion, the porosome opening dilates to allow release of secretory products, returning to its resting size following completion of the process (13,15,97).…”