Sheng Z H, Westenbroek R E, Catterall W A
Synaptic Function Unit, NINDS, NIH, Bethesda, MD 20892, USA.
J Bioenerg Biomembr. 1998 Aug;30(4):335-45. doi: 10.1023/a:1021985521748.
N- and P/Q-type calcium channels are localized in high density in presynaptic nerve terminals and are crucial elements in neuronal excitation-secretion coupling. In addition to mediating Ca2+ entry to initiate transmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. As outlined in the preceding article, these calcium channels can be purified from brain as a complex with SNARE proteins which are involved in exocytosis. In addition, N-type and P/Q-type calcium channels are co-localized with syntaxin in high-density clusters in nerve terminals. Here we review the role of the synaptic protein interaction (synprint) sites in the intracellular loop II-III (L(II-III)) of both alpha1B and alpha1A subunits of N-type and P/Q-type calcium channels, which bind to syntaxin, SNAP-25, and synaptotagmin. Calcium has a biphasic effect on the interactions of N-type calcium channels with SNARE complexes, stimulating optimal binding in the range of 10-20 microM. PKC or CaM KII phosphorylation of the N-type synprint peptide inhibits interactions with native brain SNARE complexes containing syntaxin and SNAP-25. Introduction of the synprint peptides into presynaptic superior cervical ganglion neurons reversibly inhibits EPSPs from synchronous transmitter release by 42%. At physiological Ca2+ concentrations, synprint peptides cause an approximate 25% reduction in transmitter release of injected frog neuromuscular junction in cultures, consistent with detachment of 70% of the docked vesicles from calcium channels based on a theoretical model. Together, these studies suggest that presynaptic calcium channels not only provide the calcium signal required by the exocytotic machinery, but also contain structural elements that are integral to vesicle docking, priming, and fusion processes.
N型和P/Q型钙通道在突触前神经末梢中高密度分布，是神经元兴奋 - 分泌偶联中的关键元件。除了介导Ca2+内流以启动递质释放外，它们还被认为与突触小泡对接/融合机制的蛋白质直接相互作用。如前文所述，这些钙通道可从脑中作为与参与胞吐作用的SNARE蛋白的复合物进行纯化。此外，N型和P/Q型钙通道与 syntaxin 在神经末梢的高密度簇中共定位。在此，我们综述N型和P/Q型钙通道的α1B和α1A亚基细胞内环II - III（L(II - III)）中与 syntaxin、SNAP - 25和突触结合蛋白结合的突触蛋白相互作用（synprint）位点的作用。钙对N型钙通道与SNARE复合物的相互作用具有双相效应，在10 - 20 microM范围内刺激最佳结合。N型synprint肽的PKC或CaM KII磷酸化抑制与含有 syntaxin 和SNAP - 25的天然脑SNARE复合物的相互作用。将synprint肽引入突触前颈上神经节神经元可使同步递质释放产生的兴奋性突触后电位（EPSP）可逆性抑制42%。在生理Ca2+浓度下，synprint肽使培养的注射蛙神经肌肉接头的递质释放减少约25%，基于理论模型这与70%的对接小泡从钙通道脱离一致。总之，这些研究表明突触前钙通道不仅提供胞吐机制所需的钙信号，还包含对小泡对接、引发和融合过程不可或缺的结构元件。
