Synaptic vesicles (SVs) release neuronal transmitters by the fusion with the presynaptic membrane (PM), and the SV protein Synaptotagmin 1 (Syt1) serves as a calcium sensor for evoked fusion. Syt1 is thought to trigger fusion by penetrating into PM upon calcium binding, however the mechanistic detail of this process are still debated. Syt1 interacts with the SNARE complex, a coiled-coil four-helical bundle that mediates the SV-PM attachment, and the protein Complexin (Cpx) attaches to the SNARE bundle and promotes calcium-dependent fusion. We employed all-atom molecular dynamics (MD) to investigate the formation of the Syt1-SNARE-Cpx complex interacting with PM and SV. Our simulations demonstrated that the PM-Syt1-SNARE-Cpx complex can transition to a dead-end state, wherein Syt1 attaches tightly to PM but does not immerse into it, as opposed to a pre-fusion state, which has the tips of the calcium-bound C2 domains of Syt1 inserted into PM. We simulated the sequence of Syt1 conformational transitions, including Syt1 docking to the SNARE bundle and PM, as well as calcium chelation, and found that the direct Syt1-Cpx interaction is required to promote these transitions. We developed the all-atom dynamic model of the Cpx-mediated sequence of conformational transitions that lead to the formation of the pre-fusion state of the PM-Syt1-SNARE-Cpx complex. We also show that an alternative dead-end complex can be formed if this pathway is disrupted.

中文翻译：

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蛋白质-脂质融合前状态的动态形成

突触小泡 (SV) 通过与突触前膜 (PM) 融合来释放神经递质，SV 蛋白 Synaptotagmin 1 (Syt1) 充当诱发融合的钙传感器。 Syt1被认为通过钙结合后渗透到PM中来触发融合，但是这个过程的机制细节仍然存在争议。 Syt1 与 SNARE 复合体（介导 SV-PM 附着的卷曲螺旋四螺旋束）相互作用，并且蛋白质复合物 (Cpx) 附着在 SNARE 束上并促进钙依赖性融合。我们采用全原子分子动力学 (MD) 来研究与 PM 和 SV 相互作用的 Syt1-SNARE-Cpx 复合物的形成。我们的模拟表明，PM-Syt1-SNARE-Cpx 复合体可以转变为死端状态，其中 Syt1 紧密附着在 PM 上，但不会浸入其中，这与融合前状态相反，融合前状态具有Syt1 的钙结合 C2 结构域插入 PM。我们模拟了 Syt1 构象转变的序列，包括 Syt1 与 SNARE 束和 PM 的对接，以及钙螯合，并发现直接的 Syt1-Cpx 相互作用是促进这些转变所必需的。我们开发了 Cpx 介导的构象转变序列的全原子动力学模型，该序列导致 PM-Syt1-SNARE-Cpx 复合物融合前状态的形成。我们还表明，如果该途径被破坏，则可以形成替代的死胡同复合物。