Synaptotagmin-1 (Syt1) is a calcium sensor protein that is critical for neurotransmission and is therefore extensively studied. Here, we use pairs of optically trapped beads coated with SNARE-free synthetic membranes to investigate Syt1-induced membrane remodeling. This activity is compared with that of Doc2b, which contains a conserved C2AB domain and induces membrane tethering and hemifusion in this cell-free model. We find that the soluble C2AB domain of Syt1 strongly affects the probability and strength of membrane-membrane interactions in a strictly Ca2+- and protein-dependent manner. Single-membrane loading of Syt1 yielded the highest probability and force of membrane interactions, whereas in contrast, Doc2b was more effective after loading both membranes. A lipid-mixing assay with confocal imaging reveals that both Syt1 and Doc2b are able to induce hemifusion; however, significantly higher Syt1 concentrations are required. Consistently, both C2AB fragments cause a reduction in the membrane-bending modulus, as measured by a method based on atomic force microscopy. This lowering of the energy required for membrane deformation may contribute to Ca2+-induced fusion.

中文翻译：

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Synaptotagmin-1 和 Doc2b 表现出不同的膜重塑机制

Synaptotagmin-1 (Syt1) 是一种钙传感器蛋白，对神经传递至关重要，因此得到了广泛的研究。在这里，我们使用涂有无 SNARE 合成膜的光学捕获珠对来研究 Syt1 诱导的膜重塑。将此活性与 Doc2b 的活性进行比较，Doc2b 包含一个保守的 C2AB 结构域并在此无细胞模型中诱导膜束缚和半融合。我们发现 Syt1 的可溶性 C2AB 结构域以严格的 Ca2+- 和蛋白质依赖性方式强烈影响膜-膜相互作用的概率和强度。Syt1 的单膜加载产生了最高的膜相互作用概率和力，而相比之下，Doc2b 在加载两种膜后更有效。共聚焦成像的脂质混合试验表明 Syt1 和 Doc2b 都能够诱导半融合；然而，需要显着更高的 Syt1 浓度。一致地，两种 C2AB 片段都会导致膜弯曲模量降低，这是通过基于原子力显微镜的方法测量的。这种膜变形所需能量的降低可能有助于 Ca2+ 诱导的融合。