Role of the cytoplasmic protein synaphin in the process of transmitter release

Synphin是一种胞质蛋白，我们首次发现它与对接/融合复合体有关，而对接/融合复合体对递质释放至关重要。这项研究的目的是阐明该蛋白在释放过程中的功能。我们获得了以下结果：(1)脑内分布与进化保守脑内存在两种不同类型的突触蛋白(突触蛋白1和突触蛋白2：84%相同)。这两种异构体在大脑皮层、丘脑、小脑和杏仁核等脑区均有不同的分布，表明这两种异构体具有不同的生理意义。与哺乳动物非常相似的突触素存在于鱼类中，无脊椎动物的神经系统中也含有这些蛋白质。(2)功能当将与突触素的部分氨基酸序列相对应的多肽注入鱿鱼巨型突触的突触前末端时，递质释放迅速受到抑制。该肽抑制突触素与突触素的结合，但不影响SNARE相互作用、突触小泡停靠或钙通道功能。因此，突触素/合成素的相互作用对递质的释放至关重要。重组SNARE蛋白与突触素的体外结合实验表明，单靠突触素结合的突触素很少。然而，突触囊泡蛋白VAMP(Synaptobrevin)显著促进了突触蛋白与突触蛋白的结合。相反，突触素可显著增加VAMP对突触素的亲和力。综上所述，这些结果表明，突触素/SNARE相互作用在突触小泡对接和融合之间起着至关重要的作用。

Synaphin is a cytosolic protein we first found to be associated with the docking/fusion complex that is critical to transmitter release. The goal of this study was to clarify the function of this protein in the release process. We have obtained following results.(1) Distribution in the brain and tevolutionary conservationTwo isoforms of synaphin (synaphins 1 and 2 : 84% identical) exist in the brain. The two isoforms are distictly distributed in the brain regions such as cerebral cortex, thalamus, cerebellum and amygdaloid., indicating different physiological implications for the isoforms. Synaphins very similar to mammalian ones are present in fish, and an invertebrate nervous system also contains the proteins.(2) FunctionWhen a peptide corresponding to a partial amino acid sequence of synaphin was injected into the presynaptic terminal of the squid giant synapse, transmitter release was rapidly inhibited. This peptide inhibited binding of synaphin to syntaxin but did not affect SNARE interactions, synaptic vesicle docking or calcium channel functions. Thus synaphin/syntaxin interaction is essential for transmitter release. In vitro binding experiments between recombinant SNARE proteins and synaphin show that syntaxin alone binds very little synaphin. However, the synaptic vesicle protein VAMP (synaptobrevin) markedly facilitated syntaxin binding to synaphin. Conversely, synaphin geatly increased the affinity of VAMP to syntaxin. Taken together, these results indicate that synaphin/SNARE interactions play an essential role at a step between synaptic vesicle docking and fusion.