Lindau M, Almers W
Abteilung Molekulare Zellforschung, Max Planck Institut für medizinische Forschung, Heidelberg, Germany.
Curr Opin Cell Biol. 1995 Aug;7(4):509-17. doi: 10.1016/0955-0674(95)80007-7.
Several proteins involved in exocytosis have been identified recently, but it is still completely unclear which molecules perform the fusion event itself. Although in viral fusion the fusion proteins are known, even there the molecular mechanism remains controversial. Investigation of single fusion events by electrophysiological techniques together with fluorimetric measurements have now provided some insight into the properties of the first aqueous connection, the fusion pore. This pore has an initial size similar to an ion channel and allows movement of lipids only after it has substantially expanded, indicating that it is initially not a purely lipidic structure, but incorporates lipids when it expands. Although neurotransmitter release may occur through narrow transient fusion pores, the fusion pore of synaptic vesicles probably expands vey rapidly, making it unlikely that secretion is performed by rapid exo/endocytosis without full fusion under normal conditions. Recent recordings from small membrane patches have made it possible to resolve fusion events from vesicles as small as synaptic vesicles. Future experiments using excised patches may provide an approach to identify the molecular machinery of exocytotic membrane fusion.
最近已经鉴定出几种参与胞吐作用的蛋白质，但目前仍完全不清楚究竟是哪些分子执行融合过程本身。尽管在病毒融合中融合蛋白是已知的，但即便如此分子机制仍存在争议。通过电生理技术和荧光测量对单个融合事件进行研究，现在已经对首个水性连接通道即融合孔的特性有了一些了解。这个孔的初始大小类似于离子通道，并且只有在其大幅扩张后才允许脂质移动，这表明它最初不是纯粹的脂质结构，而是在扩张时纳入脂质。尽管神经递质释放可能通过狭窄的瞬时融合孔发生，但突触小泡的融合孔可能迅速扩张，这使得在正常情况下通过快速胞吐/内吞而不发生完全融合来进行分泌不太可能。最近从小膜片上进行的记录使得分辨来自像突触小泡那么小的囊泡的融合事件成为可能。未来使用切除膜片的实验可能会提供一种鉴定胞吐性膜融合分子机制的方法。
