Interactions between two divalent ion binding sites in N-methyl-D-aspartate receptor channels
Interactions between two divalent ion binding sites in N-methyl-D-aspartate receptor channels
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DOI：
10.1073/pnas.93.24.14170
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发表时间：
1996-11-26
影响因子：
11.1
通讯作者：
Stevens, CF
中科院分区：
文献类型：
--
作者：
Sharma, G;Stevens, CF
N-甲基-D-天冬氨酸受体通道表现出对钙离子的高通透性，在本报告中，我们证实了钙离子有效地通过野生型通道，并发现它们在孔内的存在阻止了钠和其他离子的流动，进一步的证据来自于对epsilon 1(N614Q)突变的分析，其中钙离子的高通透性没有变化，但被钙离子的阻挡增加了一倍。在野生型和突变型通道中，钙离子阻断不依赖于膜电压；因此，钙离子的结合部位在通过孔的电压梯度之外，必须靠近离子电导途径的胞外口，这个钙部位不同于镁离子结合部位，镁离子结合部位80%进入孔的静电场中，因此表现出明显的电压依赖性结合。epsilon 1(N614Q)突变降低了镁离子对其结合部位的亲和力，但增加了钙离子对其结合部位的亲和力，由于单个突变以相反的方式扰乱了两个不同的结合部位，我们推测这两个位点上的二价离子结合是相互作用的。
N-methyl-D-aspartate receptor channels exhibit a high permeability for calcium ions, In this report, we confirm that calcium ions permeate effectively through the wild-type channels, and find that their presence within the pore blocks the flux of sodium and other ions, Further proof for this ionic block comes from the analysis of the epsilon 1(N614Q) mutation where the high permeability of calcium is unchanged but the block by calcium ions is increased twofold. In both the wild-type and mutant channels, calcium ion block is independent of membrane voltage; therefore, the calcium binding site is outside the voltage gradient through the pore and must be close to the extracellular mouth of the ion conductance pathway, This calcium site is distinct from the magnesium binding site, which lies 80% into the pore's electrostatic field and thus exhibits a marked voltage dependence of binding, The epsilon 1(N614Q) mutation reduces the affinity of magnesium ion for its binding site but increases the affinity of calcium ion for its binding site, Since a single mutation perturbs two distinct binding sites in opposite ways, we postulate that binding of divalent ions at the two sites interact.