Degtiar V E, Scheller R H, Tsien R W
Department of Molecular and Cellular Physiology, Beckman Center, and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA.
J Neurosci. 2000 Jun 15;20(12):4355-67. doi: 10.1523/JNEUROSCI.20-12-04355.2000.
Syntaxin, a membrane protein vital in triggering vesicle fusion, interacts with voltage-gated N- and P/Q-type Ca(2+) channels. This biochemical association is proposed to colocalize Ca(2+) channels and presynaptic release sites, thus supporting rapid and efficient initiation of neurotransmitter release. The syntaxin channel interaction may also support a novel signaling function, to modulate Ca(2+) channels according to the state of the associated release machinery (Bezprozvanny et al., 1995; Wiser et al., 1996; see also Mastrogiacomo et al., 1994). Here we report that syntaxin 1A (syn1A) coexpressed with N-type channels in Xenopus oocytes greatly promoted slow inactivation gating, but had little or no effect on the onset of and recovery from fast inactivation. Accordingly, the effectiveness of syntaxin depended strongly on voltage protocol. Slow inactivation was found for N-type channels even in the absence of syntaxin and could be distinguished from fast inactivation on the basis of its slow kinetics, distinct voltage dependence (voltage-independent at potentials higher than the level of half-inactivation), and temperature independence (Q(10), approximately 0.8). Trains of action potential-like stimuli were more effective than steady depolarizations in stabilizing the slowly inactivated condition. Agents that stimulate protein kinase C decreased the inhibitory effect of syntaxin on N-type channels. Application of BoNtC1 to cleave syntaxin sharply attenuated the modulatory effects on Ca(2+) channel gating, consistent with structural analysis of syntaxin modulation, supporting use of this toxin to test for the impact of syntaxin on Ca(2+) influx in nerve terminals.
syntaxin是一种在触发囊泡融合中起关键作用的膜蛋白，它与电压门控的N型和P/Q型Ca(2+)通道相互作用。这种生化关联被认为可使Ca(2+)通道与突触前释放位点共定位，从而支持神经递质释放的快速高效启动。 syntaxin与通道的相互作用还可能支持一种新的信号功能，即根据相关释放机制的状态调节Ca(2+)通道（Bezprozvanny等人，1995年；Wiser等人，1996年；另见Mastrogiacomo等人，1994年）。在此我们报告，在非洲爪蟾卵母细胞中与N型通道共表达的syntaxin 1A（syn1A）极大地促进了慢失活门控，但对快失活的起始和恢复几乎没有影响。因此，syntaxin的有效性在很大程度上取决于电压方案。即使在没有syntaxin的情况下，N型通道也会出现慢失活，并且可以根据其缓慢的动力学、独特的电压依赖性（在高于半失活水平的电位下与电压无关）和温度独立性（Q(10)，约为0.8）与快失活区分开来。一连串类似动作电位的刺激在稳定慢失活状态方面比稳定去极化更有效。刺激蛋白激酶C的试剂会降低syntaxin对N型通道的抑制作用。应用BoNtC1切割syntaxin会显著减弱对Ca(2+)通道门控的调节作用，这与syntaxin调节的结构分析一致，支持使用这种毒素来测试syntaxin对神经末梢Ca(2+)内流的影响。
