Chanda Baron, Asamoah Osei Kwame, Blunck Rikard, Roux Benoît, Bezanilla Francisco
Departments of Physiology and Anesthesiology, David Geffen School of Medicine, UCLA, 650 Charles E. Young Dr. South, Los Angeles, California 90025, USA.
Nature. 2005 Aug 11;436(7052):852-6. doi: 10.1038/nature03888.
Voltage-gated ion channels are responsible for generating electrical impulses in nerves and other excitable cells. The fourth transmembrane helix (S4) in voltage-gated channels is the primary voltage-sensing unit that mediates the response to a changing membrane electric field. The molecular mechanism of voltage sensing, particularly with respect to the magnitude of the transmembrane movement of S4, remains controversial. To determine the extent of this transmembrane movement, we use fluorescent resonance energy transfer between the S4 domain and a reference point in the lipid bilayer. The lipophilic ion dipicrylamine distributes on either side of the lipid bilayer depending on the membrane potential, and is used here as a resonance-energy-transfer acceptor from donor molecules attached to several positions in the Shaker K+ channel. A voltage-driven transmembrane movement of the donor should produce a transient fluorescence change because the acceptor also translocates as a function of voltage. In Shaker K+ channels no such transient fluorescence is observed, indicating that the S4 segment does not translocate across the lipid bilayer. Based on these observations, we propose a molecular model of voltage gating that can account for the observed 13e gating charge with limited transmembrane S4 movement.
电压门控离子通道负责在神经和其他可兴奋细胞中产生电冲动。电压门控通道中的第四个跨膜螺旋（S4）是主要的电压感应单元，介导对变化的膜电场的响应。电压感应的分子机制，特别是关于S4跨膜运动的幅度，仍然存在争议。为了确定这种跨膜运动的程度，我们利用了S4结构域与脂质双层中的一个参考点之间的荧光共振能量转移。亲脂性离子二硝基苯胺根据膜电位分布在脂质双层的两侧，并在此用作来自连接到Shaker K+通道中几个位置的供体分子的共振能量转移受体。供体的电压驱动跨膜运动会产生瞬时荧光变化，因为受体也会随着电压而移位。在Shaker K+通道中未观察到这种瞬时荧光，表明S4片段不会跨脂质双层移位。基于这些观察结果，我们提出了一种电压门控的分子模型，该模型可以解释在有限的跨膜S4运动情况下观察到的13e门控电荷。
