Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Mol Cell Neurosci. 2010 Dec;45(4):389-97. doi: 10.1016/j.mcn.2010.07.012. Epub 2010 Jul 30.
The SNARE-binding protein complexin (Cpx) has been demonstrated to regulate synaptic vesicle fusion. Previous studies are consistent with Cpx functioning either as a synaptic vesicle fusion clamp to prevent premature exocytosis, or as a facilitator to directly stimulate release. Here we examined conserved roles of invertebrate and mammalian Cpx isoforms in the regulation of neurotransmitter release using the Drosophila neuromuscular junction as a model synapse. We find that SNARE binding by Cpx is required for its role as a fusion clamp. All four mammalian Cpx proteins (mCpx), which have been demonstrated to facilitate release, also function as fusion clamps when expressed in Drosophila cpx null mutants, though their clamping abilities vary between isoforms. Moreover, expression of mCpx I, II or III isoforms dramatically enhance evoked release compared to mCpx IV or Drosophila Cpx. Differences in the clamping and facilitating properties of complexin isoforms can be partially attributed to differences in the C-terminal membrane tethering domain. Our findings indicate that the function of complexins as fusion clamps and facilitators of fusion are conserved across evolution, and that these roles are genetically separable within an isoform and across different isoforms.
SNARE 结合蛋白复合物素（Cpx）已被证明可调节突触囊泡融合。先前的研究表明，Cpx 可以作为突触囊泡融合的夹具来防止过早的胞吐作用，也可以作为直接刺激释放的促进剂。在这里，我们使用果蝇肌肉接点作为模型突触，研究了无脊椎动物和哺乳动物 Cpx 同工型在神经递质释放调节中的保守作用。我们发现，Cpx 通过 SNARE 结合来发挥其作为融合夹具的作用。所有四种已被证明可促进释放的哺乳动物 Cpx 蛋白（mCpx），当在果蝇 cpx 缺失突变体中表达时，也可作为融合夹具发挥作用，尽管它们的夹具能力在同工型之间有所不同。此外，与 mCpx IV 或果蝇 Cpx 相比，mCpx I、II 或 III 同工型的表达可显著增强诱发释放。复合物素同工型的夹断和促进特性的差异部分归因于 C 端膜系留域的差异。我们的研究结果表明，复合物素作为融合夹具和融合促进剂的功能在进化中是保守的，并且这些功能在同工型内和不同同工型之间是可遗传分离的。
