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

突触蛋白是一种胞质蛋白，我们首先发现与对接/融合复合物，这是至关重要的发射释放。本研究的目的是阐明这种蛋白在释放过程中的功能。我们得到了以下结果。(1)脑中的分布和进化的保守性脑中存在两种突触素异构体（突触素1和2：84%相同）。这两种异构体分别分布于大脑皮层、丘脑、小脑和杏仁核等脑区，表明同种型的不同生理学意义。与哺乳动物非常相似的突触蛋白存在于鱼类中，无脊椎动物的神经系统也含有这种蛋白质。(2)当一种与突触蛋白的部分氨基酸序列相对应的肽被注射到鱿鱼巨大突触的突触前末端时，递质释放被迅速抑制。该肽抑制突触蛋白与突触融合蛋白的结合，但不影响SNARE相互作用、突触囊泡对接或钙通道功能。因此，突触蛋白/突触融合蛋白相互作用是必不可少的递质释放。重组SNARE蛋白和突触蛋白之间的体外结合实验表明，突触融合蛋白单独结合非常少的突触蛋白。然而，突触囊泡蛋白VAMP（synaptobrevin）显着促进syntaxin结合synaphin。相反，synaphin大大增加VAMP与syntaxin的亲和力。总之，这些结果表明，突触蛋白/SNARE相互作用发挥了重要作用，在突触囊泡对接和融合之间的一个步骤。

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.