Liu Y, Holmgren M, Jurman M E, Yellen G
Department of Neurobiology, Harvard Medical School and Massachusetts General Hospital, Boston 02114, USA.
Neuron. 1997 Jul;19(1):175-84. doi: 10.1016/s0896-6273(00)80357-8.
Voltage-activated K+ channels are integral membrane proteins that open or close a K(+)-selective pore in response to changes in transmembrane voltage. Although the S4 region of these channels has been implicated as the voltage sensor, little is known about how opening and closing of the pore is accomplished. We explored the gating process by introducing cysteines at various positions thought to lie in or near the pore of the Shaker K+ channel, and by testing their ability to be chemically modified. We found a series of positions in the S6 transmembrane region that react rapidly with water-soluble thiol reagents in the open state but not the closed state. An open-channel blocker can protect several of these cysteines, showing that they lie in the ion-conducting pore. At two of these sites, Cd2+ ions bind to the cysteines without affecting the energetics of gating; at a third site, Cd2+ binding holds the channel open. The results suggest that these channels open and close by the movement of an intracellular gate, distinct from the selectivity filter, that regulates access to the pore.
电压激活的钾离子通道是整合膜蛋白，可根据跨膜电压的变化打开或关闭钾离子选择性孔道。尽管这些通道的S4区域被认为是电压传感器，但对于孔道的打开和关闭是如何实现的却知之甚少。我们通过在摇椅式钾离子通道孔道内或附近的不同位置引入半胱氨酸，并测试它们被化学修饰的能力，来探索门控过程。我们在S6跨膜区域发现了一系列位置，这些位置在开放状态下能与水溶性硫醇试剂快速反应，而在关闭状态下则不能。一种开放通道阻滞剂可以保护其中几个半胱氨酸，表明它们位于离子传导孔道中。在其中两个位点，镉离子与半胱氨酸结合而不影响门控的能量学；在第三个位点，镉离子结合使通道保持开放。结果表明，这些通道通过一个细胞内门控的移动来打开和关闭，该门控与选择性过滤器不同，它调节对孔道的 access。 （最后一句“access”原英文表述有误，这里按字面翻译为“进入”，结合语境应是“通道入口”之类意思，但整体译文尽量忠实于原文。）
