Department of Membrane Biophysics, Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany.
Science. 2010 Oct 22;330(6003):502-5. doi: 10.1126/science.1193134. Epub 2010 Sep 16.
Exocytosis requires formation of SNARE [soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor] complexes between vesicle and target membranes. Recent assessments in reduced model systems have produced divergent estimates of the number of SNARE complexes needed for fusion. Here, we used a titration approach to answer this question in intact, cultured chromaffin cells. Simultaneous expression of wild-type SNAP-25 and a mutant unable to support exocytosis progressively altered fusion kinetics and fusion-pore opening, indicating that both proteins assemble into heteromeric fusion complexes. Expressing different wild-type:mutant ratios revealed a third-power relation for fast (synchronous) fusion and a near-linear relation for overall release. Thus, fast fusion typically observed in synapses and neurosecretory cells requires at least three functional SNARE complexes, whereas slower release might occur with fewer complexes. Heterogeneity in SNARE-complex number may explain heterogeneity in vesicular release probability.
胞吐作用需要在囊泡和靶膜之间形成 SNARE（可溶性 N-乙基马来酰亚胺敏感因子附着蛋白 (SNAP) 受体）复合物。最近在简化模型系统中的评估对融合所需 SNARE 复合物的数量产生了不同的估计。在这里，我们使用滴定法在完整的培养嗜铬细胞中回答这个问题。野生型 SNAP-25 和一种不能支持胞吐作用的突变体的同时表达逐渐改变了融合动力学和融合孔的打开，表明这两种蛋白都组装成异源融合复合物。表达不同的野生型：突变型比例显示快速（同步）融合呈三次方关系，而总释放呈近线性关系。因此，在突触和神经分泌细胞中通常观察到的快速融合至少需要三个功能 SNARE 复合物，而较慢的释放可能需要较少的复合物。SNARE 复合物数量的异质性可能解释了囊泡释放概率的异质性。
