Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA.
Nat Neurosci. 2011 Dec 25;15(2):243-9. doi: 10.1038/nn.3013.
Synaptotagmin I (syt1) is required for normal rates of synaptic vesicle endo- and exocytosis. However, whether the kinetic defects observed during endocytosis in Syt1 knockout neurons are secondary to defective exocytosis or whether syt1 directly regulates the rate of vesicle retrieval remains unknown. To address this question, we sought to dissociate these two activities. We uncoupled the function of syt1 in exo- and endocytosis in mouse neurons either by re-targeting the protein or via mutagenesis of its tandem C2 domains. The effect of these manipulations on exo- and endocytosis were analyzed using electrophysiology, in conjunction with optical imaging of the vesicle cycle. Our results indicate that syt1 is directly involved in endocytosis. Notably, either of the C2 domains of syt1, C2A or C2B, was able to function as a Ca(2+) sensor for endocytosis. Thus, syt1 functions as a dual Ca(2+) sensor for both endo- and exocytosis, potentially coupling these two components of the vesicle cycle.
突触融合蛋白 I（syt1）对于正常的突触小泡内吞和胞吐速率是必需的。然而，在 Syt1 敲除神经元中观察到的内吞过程中的动力学缺陷是继发于胞吐作用缺陷，还是 syt1 直接调节小泡回收的速率，目前尚不清楚。为了解决这个问题，我们试图将这两种活性分离开来。我们通过重新靶向该蛋白或突变其串联 C2 结构域，使小鼠神经元中的 syt1 的内吞和胞吐功能解偶联。使用电生理学以及囊泡循环的光学成像，结合分析这些操作对内吞和胞吐作用的影响。我们的结果表明 syt1 直接参与内吞作用。值得注意的是，syt1 的两个 C2 结构域（C2A 或 C2B）中的任一个都可以作为内吞作用的 Ca2+ 传感器发挥作用。因此，syt1 作为内吞和胞吐作用的双重 Ca2+ 传感器发挥作用，可能将囊泡循环的这两个组成部分偶联起来。
