A novel function for the second C2 domain of synaptotagmin - Ca2+-triggered dimerization
A novel function for the second C2 domain of synaptotagmin - Ca2+-triggered dimerization
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DOI：
10.1074/jbc.271.10.5844
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发表时间：
1996-03-08
影响因子：
4.8
通讯作者：
Jahn, R
中科院分区：
文献类型：
--
作者：
Chapman, ER;An, S;Jahn, R
突触结合蛋白是调节神经元胞吐作用的主要 Ca2+ 传感器。虽然突触结合蛋白调节膜融合的机制仍不清楚，但使用果蝇的研究表明，该分子作为多聚体复合物发挥作用，并且其第二个 C2 结构域对于有效的激发-分泌耦合至关重要。在这里，我们描述了可以解释这些现象的生化数据。我们报告 Ca2+ 导致突触结合蛋白通过其第二个 C2 结构域寡聚化，主要形成二聚体。这种效应是二价阳离子所特有的，可刺激突触小泡的胞吐作用（Ca2+ >> Ba2+、Sr2+ >> > Mg2+），且 EC(50) 值为 3-10 μM Ca2+ 时会发生这种效应。相反，突触结合蛋白和突触结合蛋白（融合装置的一个组成部分）之间存在独立的 Ca2+ 依赖性相互作用，其 EC(50) 值类似于 100 μM Ca2+，并且涉及突触结合蛋白的两个 C2 结构域的协同作用。我们认为 Ca2+ 触发两个连续的蛋白质-蛋白质相互作用：在低 Ca2+ 浓度下形成突触结合蛋白二聚体，随后在较高 Ca2+ 浓度下突触结合蛋白二聚体与突触结合蛋白缔合。我们的研究结果与生理学研究相结合，表明 Ca2+ 诱导的突触结合蛋白二聚化对于 Ca2+ 胞吐作用的有效调节非常重要。
Synaptotagmin serves as the major Ca2+ sensor for regulated exocytosis from neurons. While the mechanism by which synaptotagmin regulates membrane fusion remains unknown, studies using Drosophila indicate that the molecule functions as a multimeric complex and that its second C2 domain is essential for efficient excitation-secretion coupling. Here we describe biochemical data that may account for these phenomena. We report that Ca2+ causes synaptotagmin to oligomerize, primarily forming dimers, via its second C2 domain. This effect is specific for divalent cations that can stimulate exocytosis of synaptic vesicles (Ca2+ >> Ba2+, Sr2+ >> > Mg2+) and occurs with an EC(50) value of 3-10 mu M Ca2+. In contrast, a separate Ca2+-dependent interaction between synaptotagmin and syntaxin, a component of the fusion apparatus, occurs with an EC(50) value of similar to 100 mu M Ca2+ and involves the synergistic action of both C2 domains of synaptotagmin. We propose that Ca2+ triggers two consecutive protein-protein interactions: the formation of synaptotagmin dimers at low Ca2+ concentrations followed by the association of synaptotagmin dimers with syntaxin at higher Ca2+ concentrations. Our findings, in conjunction with physiological studies, indicate that the Ca2+-induced dimerization of synaptotagmin is important for the efficient regulation of exocytosis by Ca2+.