Holmgren M, Shin K S, Yellen G
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Neuron. 1998 Sep;21(3):617-21. doi: 10.1016/s0896-6273(00)80571-1.
Voltage-activated K+ channels are integral membrane proteins containing a potassium-selective transmembrane pore gated by changes in the membrane potential. This activation gating (opening) occurs in milliseconds and involves a gate at the cytoplasmic side of the pore. We found that substituting cysteine at a particular position in the last transmembrane region (S6) of the homotetrameric Shaker K+ channel creates metal binding sites at which Cd2+ ions can bind with high affinity. The bound Cd2+ ions form a bridge between the introduced cysteine in one channel subunit and a native histidine in another subunit, and the bridge traps the gate in the open state. These results suggest that gating involves a rearrangement of the intersubunit contacts at the intracellular end of S6. The recently solved structure of a bacterial K+ channel shows that the S6 homologs cross in a bundle, leaving an aperture at the bundle crossing. In the context of this structure, the metal ions form a bridge between a cysteine above the bundle crossing and a histidine below the bundle crossing in a neighboring subunit. Our results suggest that gating occurs at the bundle crossing, possibly through a change in the conformation of the bundle itself.
电压门控钾离子通道是整合膜蛋白，包含一个由膜电位变化控制的钾离子选择性跨膜孔道。这种激活门控（开放）过程在数毫秒内发生，且涉及孔道胞质侧的一个门控结构。我们发现，在同四聚体Shaker钾离子通道最后一个跨膜区域（S6）的特定位置替换半胱氨酸会产生金属结合位点，镉离子（Cd2+）能以高亲和力结合于这些位点。结合的镉离子在一个通道亚基中引入的半胱氨酸与另一个亚基中的天然组氨酸之间形成一座桥，这座桥将门控结构锁定在开放状态。这些结果表明，门控涉及S6细胞内端亚基间接触的重排。最近解析的一种细菌钾离子通道结构显示，S6同源物呈束状交叉，在束状交叉处留下一个孔隙。在这种结构背景下，金属离子在相邻亚基中束状交叉上方的半胱氨酸与束状交叉下方的组氨酸之间形成一座桥。我们的结果表明，门控发生在束状交叉处，可能是通过束状结构本身构象的改变来实现的。
