Functional studies on steric structure of ion channels -supporting voltage-dependent fluctuations of voltage-sensor domains of ion channels in lipid bilayer membrane-

在钾离子通道晶体结构的研究中，Mackinnon等（2003）展示了离子通道的立体结构图像。根据他们的研究，电压传感器域在孔域外的脂质双层膜上随电压波动。西卡毒素（Mw略大于1000）由13个醚环（A ~ M环）组成，具有脂溶性，结构相对刚性，选择性激活电压依赖性钠通道（VDSC）。该毒素的这些明显特征可能有助于通过分析雪卡毒素与VDSC的相互作用来阐明VDSC的空间结构。通过这样做，我们得到了关于VDSC结构信息的四个重要结果。1. 合成的雪卡毒素之一，CTX3C选择性作用于VDSC的4个跨膜结构域中的2域。2. 生物化CTX3C或51-OH-CTX3C在B环的实验表明，分子的A或B环侧作为雪卡毒素的官能团。3. f环的细微结构变化（从原来的9元f环转变为8元或10元f环）导致CTX3C作用效能显著降低。4. CTX3C通过作用于河豚毒素敏感Na通道Na_<v>1.2和Na_<v>1.4的分子结构域2，优先调节河豚毒素抗性痛觉钠通道Na_<v>1.8。这些结果表明结构域2在VDSC结构研究中的重要性。

An image of steric structure of ion channels has been illustrated by Mackinnon at al (2003) in the studies of crystal structure of potassium channels. According to them, voltage sensor domains fluctuate voltage-dependently in the lipid bilayer membrane outside of pore domains. Ciguatoxins (Mw is just over 1000) are composed of 13 ether rings (A to M ring), lipid soluble, have relatively rigid structure and selectively activate voltage-dependent sodium channels (VDSC). Theses distinct features of this toxin may well contribute to elucidating steric structure of VDSC by analyzing interaction of ciguatoxins and VDSC. By doing this, we obtained four important results regarding structural information of VDSC. 1. One of the synthesized ciguatoxin, CTX3C selectively acts on domain 2 of 4 membrane-spanning domains of VDSC. 2. Experiments using biotinized CTX3C or 51-OH-CTX3C at B-ring indicated that A or B ring side of the molecule acts as functional group of cigatoxins. 3. Subtle structural changes in F-ring (structural alteration of original 9-membered F-ring to 8 or 10-membered ring) induced important reduction in potency of CTX3C action. 4. CTX3C preferentially modulates tetrodotoxin-resistant pain-sensing sodium channel, Na_<v>1.8, through acting on domain 2 of the molecule over tetrodotoxin-sensitive Na channels, Na_<v>1.2 and Na_<v>1.4. These results indicate importance of domain 2 in the structural studies of VDSC.