DISTINCT CA2+ AND SR2+ BINDING-PROPERTIES OF SYNAPTOTAGMINS - DEFINITION OF CANDIDATE CA2+ SENSORS FOR THE FAST AND SLOW COMPONENTS OF NEUROTRANSMITTER RELEASE
DISTINCT CA2+ AND SR2+ BINDING-PROPERTIES OF SYNAPTOTAGMINS - DEFINITION OF CANDIDATE CA2+ SENSORS FOR THE FAST AND SLOW COMPONENTS OF NEUROTRANSMITTER RELEASE
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DOI：
10.1074/jbc.270.42.24898
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发表时间：
1995-10-20
影响因子：
4.8
通讯作者：
SUDHOF, TC
中科院分区：
文献类型：
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作者：
LI, C;DAVLETOV, BA;SUDHOF, TC
Ca 2+依赖性神经递质释放由至少两种组分组成：对Sr 2+不敏感的主要快组分和被Sr 2+增强的次要慢组分（Goda，Y.，和Stevens，C. F.等人（1994）Proc. Acad.联合S. A. 91，12942-12946）。这些结果表明，至少有两个Ca 2+传感器在突触囊泡融合不同的Ca 2+和Sr 2+结合特性。我们现在已经研究了突触结合蛋白的相对Ca 2+和Sr 2+结合活性，以评估它们作为快组分和慢组分的Ca 2+传感器的潜在作用。我们的结果表明，突触结合蛋白I、II、III、V和VII的第一个C-2结构域对磷脂结合具有非常相似的Ca 2+需求（EC（50）范围= 2.6 μ M至5.0 μ M），但需要不同的Sr 2+（EC（50）范围= 23 μ M至133 μ M）;突触结合蛋白I和II的Sr ~（2+）亲和力最低，突触结合蛋白III的Sr ~（2+）亲和力最高。纯化的突触结合蛋白I从牛脑表现出类似的性质，其重组的第一个C-2结构域，这表明第一个C-2结构域完全占其钙依赖性磷脂结合特性。Sr 2+在所有测试浓度下都不能触发突触结合蛋白与突触结合蛋白I的结合，而对突触结合蛋白III有效。这些结果表明，不同的C-2结构域具有不同的Sr 2+结合特性。他们支持的假设，synaptotagmins定位在同一个囊泡执行不同的功能，与synaptotagmins I和II作为候选人的Ca 2+传感器的快速组件在释放和synaptotagmin III的缓慢组件。
Ca2+-dependent neurotransmitter release consists of at least two components: a major fast component that is insensitive to Sr2+ and a minor slow component that is potentiated by Sr2+ (Goda, Y., and Stevens, C. F. (1994) Proc. Natl. Acad. U. S. A. 91, 12942-12946). These results suggest that at least two Ca2+ sensors act in synaptic vesicle fusion with distinct Ca2+ and Sr2+ binding properties. We have now investigated the relative Ca2+ and Sr2+ binding activities of synaptotagmins to evaluate their potential roles as Ca2+ sensors for the fast and slow components. Our results demonstrate that the first C-2 domains of synaptotagmins I, II, III, V, and VII have very similar Ca2+ requirements for phospholipid binding (range of EC(50) = 2.6 mu M to 5.0 mu M), but distinct Sr2+ requirements (EC(50) range = 23 mu M to 133 mu M); synaptotagmin I and II had the lowest Sr2+ affinity, and synaptotagmin III the highest Sr2+ affinity. Purified synaptotagmin I from bovine brain exhibited similar properties as its recombinant first C-2 domain, suggesting that the first C-2 domain fully accounts for its Ca2+-dependent phospholipid binding properties. Sr2+ was unable to trigger syntaxin binding by synaptotagmin I at all concentrations tested, whereas it was effective for synaptotagmin III. These results suggest that different C-2 domains have distinct Sr2+ binding properties. They support the hypothesis that synaptotagmins localized on the same vesicle perform distinct functions, with synaptotagmins I and II serving as candidate Ca2+ sensors for the fast component in release and synaptotagmin III for the slow component.