Xue Mingshan, Ma Cong, Craig Timothy K, Rosenmund Christian, Rizo Josep
Department of Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
Nat Struct Mol Biol. 2008 Nov;15(11):1160-8. doi: 10.1038/nsmb.1508. Epub 2008 Oct 26.
Synaptotagmin-1 functions as a Ca2+ sensor in neurotransmitter release and was proposed to act on both the synaptic vesicle and plasma membranes through interactions involving the Ca2+ binding top loops of its C(2) domains and the Ca2+-independent bottom face of the C(2)B domain. However, the functional importance of the C(2)B domain bottom face is unclear. We now show that mutating two conserved arginine residues at the C(2)B domain bottom face practically abolishes synchronous release in hippocampal neurons. Reconstitution experiments reveal that Ca2+-synaptotagmin-1 can dramatically stimulate the rate of SNARE-dependent lipid mixing, and that the two-arginine mutation strongly impairs this activity. These results demonstrate that synaptotagmin-1 function depends crucially on the bottom face of the C(2)B domain and strongly support the notion that synaptotagmin-1 triggers membrane fusion and neurotransmitter release by bringing the vesicle and plasma membranes together, much like the SNAREs do but in a Ca2+-dependent manner.
突触结合蛋白-1在神经递质释放过程中作为Ca2+传感器发挥作用，有人提出它通过其C(2)结构域的Ca2+结合顶环和C(2)B结构域的Ca2+非依赖性底面之间的相互作用，作用于突触小泡膜和质膜。然而，C(2)B结构域底面的功能重要性尚不清楚。我们现在表明，在C(2)B结构域底面突变两个保守的精氨酸残基实际上消除了海马神经元中的同步释放。重组实验表明，Ca2+ - 突触结合蛋白-1可以显著刺激SNARE依赖性脂质混合的速率，而双精氨酸突变强烈损害这种活性。这些结果表明，突触结合蛋白-1的功能关键取决于C(2)B结构域的底面，并有力地支持了这样一种观点，即突触结合蛋白-1通过将小泡膜和质膜聚集在一起触发膜融合和神经递质释放，这与SNAREs的作用方式类似，但以Ca2+依赖的方式进行。
