Wyszynski M, Kharazia V, Shanghvi R, Rao A, Beggs A H, Craig A M, Weinberg R, Sheng M
Howard Hughes Medical Institute and Department of Neurobiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
J Neurosci. 1998 Feb 15;18(4):1383-92. doi: 10.1523/JNEUROSCI.18-04-01383.1998.
Fast chemical neurotransmission is dependent on ionotropic receptors that are concentrated and immobilized at specific postsynaptic sites. The mechanisms of receptor clustering and anchoring in neuronal synapses are poorly understood but presumably involve molecular linkage of membrane receptor proteins to the postsynaptic cytoskeleton. Recently the actin-binding protein alpha-actinin-2 was shown to bind directly to the NMDA receptor subunits NR1 and NR2B (), suggesting that alpha-actinin-2 may function to attach NMDA receptors to the actin cytoskeleton. Here we show that alpha-actinin-2 is localized specifically in glutamatergic synapses in cultured hippocampal neurons. By immunogold electron microscopy, alpha-actinin-2 is concentrated over the postsynaptic density (PSD) of numerous asymmetric synapses where it colocalizes with NR1 immunoreactivity. Thus alpha-actinin-2 is appropriately positioned at the ultrastructural level to function as a postsynaptic-anchoring protein for NMDA receptors. alpha-Actinin-2 is not, however, exclusively found at the PSD; immunogold labeling was also associated with filaments and the spine apparatus of dendritic spines and with microtubules in dendritic shafts. alpha-Actinin-2 showed marked differential regional expression in rat brain. For instance, the protein is expressed at much higher levels in dentate gyrus than in area CA1 of the hippocampus. This differential regional expression implies that glutamatergic synapses in various parts of the brain differ with respect to their alpha-actinin-2 content and thus, potentially, the extent of possible interaction between alpha-actinin-2 and the NMDA receptor.
快速化学神经传递依赖于离子型受体，这些受体集中并固定在特定的突触后位点。人们对神经元突触中受体聚集和锚定的机制了解甚少，但推测涉及膜受体蛋白与突触后细胞骨架的分子连接。最近研究表明，肌动蛋白结合蛋白α - 辅肌动蛋白 - 2可直接与NMDA受体亚基NR1和NR2B结合，这表明α - 辅肌动蛋白 - 2可能起到将NMDA受体附着于肌动蛋白细胞骨架的作用。在此我们发现，α - 辅肌动蛋白 - 2特异性定位于培养的海马神经元的谷氨酸能突触中。通过免疫金电子显微镜观察，α - 辅肌动蛋白 - 2集中在众多不对称突触的突触后致密区（PSD），并与NR1免疫反应性共定位。因此，α - 辅肌动蛋白 - 2在超微结构水平上处于合适位置，可作为NMDA受体的突触后锚定蛋白发挥作用。然而，α - 辅肌动蛋白 - 2并非仅存在于PSD；免疫金标记还与树突棘的细丝、棘器以及树突轴中的微管相关。α - 辅肌动蛋白 - 2在大鼠脑中表现出明显的区域差异表达。例如，该蛋白在齿状回中的表达水平远高于海马体的CA1区。这种区域差异表达意味着大脑不同部位的谷氨酸能突触在α - 辅肌动蛋白 - 2含量方面存在差异，因此，α - 辅肌动蛋白 - 2与NMDA受体之间可能的相互作用程度也存在差异。
