Pombo Isabel, Rivera Juan, Blank Ulrich
Unité d'Immuno-Allergie, Institut Pasteur, Paris, France.
FEBS Lett. 2003 Aug 28;550(1-3):144-8. doi: 10.1016/s0014-5793(03)00864-0.
Exocytosis of mast cell granules requires a vesicular- and plasma membrane-associated fusion machinery. We examined the distribution of SNARE membrane fusion and Munc18 accessory proteins in lipid rafts of RBL mast cells. SNAREs were found either excluded (syntaxin2), equally distributed between raft and non-raft fractions (syntaxin4, VAMP-8, VAMP-2), or selectively enriched in rafts (syntaxin3, SNAP-23). Syntaxin4-binding Munc18-3 was absent, whereas small amounts of the syntaxin3-interacting partner Munc18-2 consistently distributed into rafts. Cognate SNARE complexes of syntaxin3 with SNAP-23 and VAMP-8 were enriched in rafts, whereas Munc18-2/syntaxin3 complexes were excluded. This demonstrates a spatial separation between these two types of complexes and suggests that Munc18-2 acts in a step different from SNARE complex formation and fusion.
肥大细胞颗粒的胞吐作用需要一种与囊泡和质膜相关的融合机制。我们研究了RBL肥大细胞脂筏中SNARE膜融合蛋白和Munc18辅助蛋白的分布。发现SNARE蛋白有的被排除在外（ syntaxin2 ），有的在脂筏和非脂筏部分中均匀分布（ syntaxin4、VAMP - 8、VAMP - 2 ），还有的在脂筏中选择性富集（ syntaxin3、SNAP - 23 ）。不存在与syntaxin4结合的Munc18 - 3 ，而少量与syntaxin3相互作用的伴侣蛋白Munc18 - 2始终分布在脂筏中。syntaxin3与SNAP - 23和VAMP - 8的同源SNARE复合体在脂筏中富集，而Munc18 - 2 / syntaxin3复合体则被排除在外。这表明这两种复合体在空间上是分离的，并提示Munc18 - 2在不同于SNARE复合体形成和融合的步骤中发挥作用。
