Mapping the membrane-aqueous border for the voltage-sensing domain of a potassium channel.
Mapping the membrane-aqueous border for the voltage-sensing domain of a potassium channel.
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DOI：
10.1074/jbc.m706437200
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发表时间：
2007-12-28
影响因子：
4.8
通讯作者：
Sivaprasadarao, Asipu
中科院分区：
文献类型：
--
作者：
Neale, Edward J;Rong, Honglin;Cockcroft, Christopher J;Sivaprasadarao, Asipu
电压传感域（VSD）在生物学中发挥着多种作用。作为不可或缺的组成部分，它们可以检测细胞膜电位的变化，并将这些变化与离子通道和酶的活性联系起来。作为独立的蛋白质，VSD的同源物可以作为电压依赖的质子通道。为了感知电压变化，带正电的第四个跨膜段S4必须穿过能量不利的双分子层疏水核心，这对带电物质和质子的运动都构成了障碍。为了减少对S4运动的障碍，有人认为水裂缝可能穿透蛋白质，降低了总运动的程度。为了在具有完整膜电位的天然环境中包含全功能通道的系统中研究这一假设，我们通过检测引入的半胱氨酸的化学可及性，确定了大肠杆菌中KvAP VSD的膜-水边界的轮廓。结果显示了VSD在激活构象中的膜-水边界轮廓。S1和S2的水不可达区域对应于膜双分子层的标准宽度（~ 28Å），但S3和S4的水不可达区域相当短（≥40%），与细胞外和细胞内两端的水裂缝一致。S3b的一个面和整个S3a都是可水的，使S3的可水区域减少到10个残基，明显短于S4。结果表明，S3在减少S4触发门控所需的移动距离方面发挥了关键作用。
Voltage sensing domains (VSD) play diverse roles in biology. As integral components, they can detect changes in the membrane potential of a cell and couple these changes to activity of ion channels and enzymes. As independent proteins, homologues of the VSD can function as voltage-dependent proton channels. To sense voltage changes, the positively charged fourth transmembrane segment, S4, must move across the energetically unfavourable hydrophobic core of the bilayer, that presents a barrier to movement of both charged species and protons. In order to reduce the barrier to S4 movement, it has been suggested that aqueous crevices may penetrate the protein, reducing the extent of total movement. To investigate this hypothesis in a system containing fully-functional channels in a native environment with an intact membrane potential, we have determined the contour of the membrane–aqueous border of the VSD of KvAP in E. coli by examining the chemical accessibility of introduced cysteines. The results revealed the contour of the membrane-aqueous border of the VSD in its activated conformation. The water-inaccessible regions of S1 and S2 correspond to the standard width of the membrane bilayer (∼28Å), but those of S3 and S4 are considerably shorter (≥40%), consistent with aqueous crevices pervading both the extracellular and intracellular ends. One face of S3b and the entire S3a were water-accessible, reducing the water-inaccessible region of S3 to just 10 residues, significantly shorter than for S4. The results suggest a key role for S3 in reducing the distance S4 needs to move to elicit gating.