Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA.
Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA.
Nat Commun. 2019 Jun 3;10(1):2413. doi: 10.1038/s41467-019-10391-x.
Synapotagmin-1 (Syt1) interacts with both SNARE proteins and lipid membranes to synchronize neurotransmitter release to calcium (Ca) influx. Here we report the cryo-electron microscopy structure of the Syt1-SNARE complex on anionic-lipid containing membranes. Under resting conditions, the Syt1 C2 domains bind the membrane with a magnesium (Mg)-mediated partial insertion of the aliphatic loops, alongside weak interactions with the anionic lipid headgroups. The C2B domain concurrently interacts the SNARE bundle via the 'primary' interface and is positioned between the SNAREpins and the membrane. In this configuration, Syt1 is projected to sterically delay the complete assembly of the associated SNAREpins and thus, contribute to clamping fusion. This Syt1-SNARE organization is disrupted upon Ca-influx as Syt1 reorients into the membrane, likely displacing the attached SNAREpins and reversing the fusion clamp. We thus conclude that the cation (Mg/Ca) dependent membrane interaction is a key determinant of the dual clamp/activator function of Synaptotagmin-1.
突触结合蛋白 1（Syt1）与 SNARE 蛋白和脂质膜相互作用，以将神经递质释放与钙（Ca）内流同步。在这里，我们报告了在含有阴离子脂质的膜上的 Syt1-SNARE 复合物的冷冻电子显微镜结构。在静息状态下，Syt1 的 C2 结构域通过镁（Mg）介导的脂环部分插入与阴离子脂质头基进行弱相互作用来结合膜。C2B 结构域通过“主要”界面同时与 SNARE 束相互作用，并位于 SNAREpins 和膜之间。在这种构象中，Syt1 被预计会在空间上延迟相关 SNAREpins 的完全组装，从而有助于夹断融合。当 Ca 流入时，这种 Syt1-SNARE 组织被破坏，因为 Syt1 重新定向到膜中，可能会置换附着的 SNAREpins 并逆转融合夹。因此，我们得出结论，阳离子（Mg/Ca）依赖性膜相互作用是突触结合蛋白 1 的双重夹断/激活功能的关键决定因素。
