Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.
Georg-August University, Department of Theoretical Physics, Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany.
Nature. 2017 Nov 30;551(7682):634-638. doi: 10.1038/nature24469. Epub 2017 Nov 1.
Membrane fusion in eukaryotic cells mediates the biogenesis of organelles, vesicular traffic between them, and exo- and endocytosis of important signalling molecules, such as hormones and neurotransmitters. Distinct tasks in intracellular membrane fusion have been assigned to conserved protein systems. Tethering proteins mediate the initial recognition and attachment of membranes, whereas SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein complexes are considered as the core fusion engine. SNARE complexes provide mechanical energy to distort membranes and drive them through a hemifusion intermediate towards the formation of a fusion pore. This last step is highly energy-demanding. Here we combine the in vivo and in vitro fusion of yeast vacuoles with molecular simulations to show that tethering proteins are critical for overcoming the final energy barrier to fusion pore formation. SNAREs alone drive vacuoles only into the hemifused state. Tethering proteins greatly increase the volume of SNARE complexes and deform the site of hemifusion, which lowers the energy barrier for pore opening and provides the driving force. Thereby, tethering proteins assume a crucial mechanical role in the terminal stage of membrane fusion that is likely to be conserved at multiple steps of vesicular traffic. We therefore propose that SNAREs and tethering proteins should be considered as a single, non-dissociable device that drives fusion. The core fusion machinery may then be larger and more complex than previously thought.
真核细胞中的膜融合介导细胞器的生物发生、它们之间的小泡运输以及激素和神经递质等重要信号分子的胞吐和胞吞作用。保守的蛋白质系统被分配到细胞内膜融合的不同任务中。 tethering proteins 介导膜的初始识别和附着，而 SNARE（可溶性 N-乙基马来酰亚胺敏感因子附着蛋白受体）蛋白复合物被认为是核心融合引擎。SNARE 复合物提供机械能量来扭曲膜，并推动它们通过半融合中间体形成融合孔。最后一步需要大量的能量。在这里，我们将酵母液泡的体内和体外融合与分子模拟相结合，表明 tethering proteins 对于克服融合孔形成的最终能量障碍至关重要。单独的 SNARE 仅将液泡驱动到半融合状态。tethering proteins 大大增加了 SNARE 复合物的体积并改变了半融合的部位，从而降低了孔打开的能量障碍并提供了驱动力。因此，tethering proteins 在膜融合的终末阶段承担着关键的机械作用，这可能在囊泡运输的多个步骤中都是保守的。因此，我们提出 SNARE 和 tethering proteins 应该被视为一个单一的、不可分离的驱动融合的装置。核心融合机制可能比以前想象的更大和更复杂。
