Stevens Charles F, Sullivan Jane M
Molecular Neurobiology Laboratory, Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
Neuron. 2003 Jul 17;39(2):299-308. doi: 10.1016/s0896-6273(03)00432-x.
Synaptotagmin is a synaptic vesicle protein that has been proposed to be the calcium sensor responsible for fast neurotransmitter release at synapses. Synaptotagmin's two C2 domains, C2A and C2B, each provide a calcium binding pocket lined with negative charges contributed by five conserved aspartates. We find that even when all of C2A's conserved aspartates are neutralized by replacement with asparagines, neurotransmitter release still occurs at hippocampal synapses in culture. Because exocytosis continues to be dependent on extracellular calcium concentration, the C2A domain cannot represent the entire calcium sensor. C2A does appear to be part of the calcium sensor, however, because substitution of D232 alters the calcium dependence of release, perhaps by reducing the number of calcium ions that must bind to trigger exocytosis. We conclude that neutralization of the negative charge at D232 by coordination of a calcium ion is necessary--but not sufficient--for fast neurotransmission at mammalian CNS synapses.
突触结合蛋白是一种突触小泡蛋白，有人提出它是负责突触快速神经递质释放的钙传感器。突触结合蛋白的两个C2结构域，即C2A和C2B，各自提供一个钙结合口袋，该口袋内衬有由五个保守天冬氨酸贡献的负电荷。我们发现，即使C2A的所有保守天冬氨酸都被天冬酰胺取代而中和，培养的海马突触中仍会发生神经递质释放。由于胞吐作用仍然依赖于细胞外钙浓度，因此C2A结构域不能代表整个钙传感器。然而，C2A似乎确实是钙传感器的一部分，因为D232的替代改变了释放的钙依赖性，这可能是通过减少必须结合以触发胞吐作用的钙离子数量来实现的。我们得出结论，通过钙离子配位使D232处的负电荷中和对于哺乳动物中枢神经系统突触的快速神经传递是必要的，但不是充分的。
