Genetic analysis of synaptotagmin-7 function in synaptic vesicle exocytosis
Genetic analysis of synaptotagmin-7 function in synaptic vesicle exocytosis
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DOI：
10.1073/pnas.0712372105
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发表时间：
2008-03-11
影响因子：
11.1
通讯作者：
Suedhof, Thomas C.
中科院分区：
文献类型：
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作者：
Maximov, Anton;Lao, Ye;Suedhof, Thomas C.
Synaptotagmin-7是一个候选的Ca 2+传感器的胞吐作用，至少部分定位于突触。类似于突触结合蛋白-1，其作为快速突触囊泡（SV）胞吐的Ca 2+传感器，突触结合蛋白-7含有表现出Ca 2+依赖性磷脂结合的C（2）A和C2B结构域。然而，synaptotagmin-7不能取代synaptotagmin-1作为一个快速SV胞吐的Ca 2+传感器，其Ca 2+结合特性的生理意义提出了疑问。在这里，我们研究如何synaptotagmin-7结合Ca 2+和测试是否这种Ca 2+结合调节Ca 2+触发SV胞吐。我们发现，synaptotagmin-7 C（2）A结构域表现出的钙离子结合模式类似的synaptotagmin-1 C2 A结构域，这表明synaptotagmin-1和-7 C-2结构域通常采用可比的钙离子结合机制。然后，我们产生了突变小鼠，缺乏synaptotagmin-7或含有点突变失活钙结合两个C-2结构域的synaptotagmin-7或仅其C2B结构域。Synaptotagmin-7突变小鼠存活且可生育。失活的Ca 2+结合到两个C-2域引起的突触结合蛋白-7水平下降约70%，而失活的Ca 2+结合到只有C2B域没有改变突触结合蛋白-7水平。synaptotagmin-7的缺失并没有改变快速同步释放，缓慢异步释放，或短期突触可塑性释放的神经递质。因此，我们的研究结果表明，Ca 2+结合的synaptotagmin-7的C-2结构域是生理上重要的稳定synaptotagmin-7，但Ca 2+结合synaptotagmin-7可能不调节SV胞吐，与synaptotagmin-7在其他形式的Ca 2+依赖性突触胞吐的作用一致。
Synaptotagmin-7 is a candidate Ca2+ sensor for exocytosis that is at least partly localized to synapses. Similar to synaptotagmin-1, which functions as a Ca2+ sensor for fast synaptic vesicle (SV) exocytosis, synaptotagmin-7 contains C(2)A and C2B domains that exhibit Ca2+- dependent phospholipid binding. However, synaptotagmin-7 cannot replace synaptotagmin-1 as a Ca2+ sensor for fast SV exocytosis, raising questions about the physiological significance of its Ca2+-binding properties. Here, we examine how synaptotagmin-7 binds Ca2+ and test whether this Ca2+ binding regulates Ca2+-triggered SV exocytosis. We show that the synaptotagmin-7 C(2)A domain exhibits a Ca2+-binding mode similar to that of the synaptotagmin-1 C2A domain, suggesting that the synaptotagmin-1 and -7 C-2 domains generally employ comparable Ca2+-binding mechanisms. We then generated mutant mice that lack synaptotagmin-7 or contain point mutations inactivating Ca2+ binding either to both C-2 domains of synaptotagmin-7 or only to its C2B domain. Synaptotagmin-7-mutant mice were viable and fertile. Inactivation of Ca2+ binding to both C-2 domains caused an approximate to 70% reduction in synaptotagmin-7 levels, whereas inactivation of Ca2+ binding to only the C2B domain did not alter synaptotagmin-7 levels. The synaptotagmin-7 deletion did not change fast synchronous release, slow asynchronous release, or short-term synaptic plasticity of release of neurotransmitters. Thus, our results show that Ca2+ binding to the synaptotagmin-7 C-2 domains is physiologically important for stabilizing synaptotagmin-7, but that Ca2+ binding by synaptotagmin-7 likely does not regulate SV exocytosis, consistent with a role for synaptotagmin-7 in other forms of Ca2+-dependent synaptic exocytosis.