Saarland University, Medical School, Department of Neuroanatomy, 66421 Homburg/Saar, Germany.
J Neurosci. 2014 Apr 9;34(15):5245-60. doi: 10.1523/JNEUROSCI.3837-13.2014.
Ribbon synapses are tonically active synapses in the retina and inner ear with intense vesicle traffic. How this traffic is organized and regulated is still unknown. Synaptic ribbons, large presynaptic structures associated with numerous synaptic vesicles, appear to be essential for this process. The base of the synaptic ribbon is anchored at the active zone and is a hotspot of exocytosis. The synaptic ribbon complex is also important for vesicle replenishment. RIBEYE is a unique and major component of synaptic ribbons. It consists of a unique A-domain and an NAD(H)-binding, C-terminal B-domain. In the present study, we show that the Arf-GTPase activating protein-3 (ArfGAP3), a well characterized regulator of vesicle formation at the Golgi apparatus, is also a component of the synaptic ribbon complex in photoreceptor synapses of the mouse retina and interacts with RIBEYE as shown by multiple, independent approaches. ArfGAP3 binds to RIBEYE(B)-domain in an NAD(H)-dependent manner. The interaction is redox sensitive because NADH is more efficient than the oxidized NAD(+) in promoting ArfGAP3-RIBEYE interaction. RIBEYE competes with the GTP-binding protein Arf1 for binding to ArfGAP3. Thus, binding of RIBEYE(B) to ArfGAP3 could prevent inactivation of Arf1 by ArfGAP3 and provides the synaptic ribbon with the possibility to control Arf1 function. The interaction is relevant for endocytic vesicle trafficking because overexpression of ArfGAP3 in photoreceptors strongly inhibited endocytotic uptake of FM1-43.
带状突触是视网膜和内耳中具有强烈囊泡运输的紧张型突触。这种运输是如何组织和调节的仍然未知。与众多突触小泡相关的大型突触前结构——突触带，似乎是这个过程所必需的。突触带的基底锚定在活性区，是胞吐作用的热点。突触带复合物对于囊泡的补充也很重要。RIBEYE 是突触带的独特主要成分。它由一个独特的 A 结构域和一个 NAD(H)结合的 C 末端 B 结构域组成。在本研究中，我们表明，Arf-GTPase 激活蛋白-3（ArfGAP3），一种在高尔基器中形成囊泡的特征调节剂，也是小鼠视网膜光感受器突触中突触带复合物的一个组成部分，如通过多种独立的方法所示，它与 RIBEYE 相互作用。ArfGAP3 以 NAD(H)依赖性的方式与 RIBEYE(B)结构域结合。这种相互作用是氧化还原敏感的，因为 NADH 比氧化态的 NAD(+)更有效地促进 ArfGAP3-RIBEYE 相互作用。RIBEYE 与 GTP 结合蛋白 Arf1 竞争与 ArfGAP3 的结合。因此，RIBEYE(B)与 ArfGAP3 的结合可以防止 ArfGAP3 使 Arf1 失活，并为突触带提供控制 Arf1 功能的可能性。这种相互作用与内吞小泡运输有关，因为在光感受器中过量表达 ArfGAP3 会强烈抑制 FM1-43 的内吞摄取。
