On the origin of closing flickers in gramicidin channels: a new hypothesis.
On the origin of closing flickers in gramicidin channels: a new hypothesis.
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DOI：
10.1016/s0006-3495(02)75488-x
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发表时间：
2002-03
影响因子：
3.4
通讯作者：
K. M. Armstrong;S. Cukierman
中科院分区：
文献类型：
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作者：
K. M. Armstrong;S. Cukierman
研究了天然甘草素A(Ga)和二氧杂环戊烷连接的Ga通道的SS和RR非对映异构体在平面双层膜中的亚毫秒关闭事件(闪烁)和单通道质子电导(Gh)。单油酸甘油酯(GMO)在不同的溶剂中形成双分子膜。在GMO/正庚烷(厚)双层膜中，最大的闪烁频率出现在SS沟道(39S−1)，其次是RR(4S−1)和自然Ga沟道(3S−1)。在GMO/角鲨烯(薄)双层膜中，这些频率在SS、RR和自然Ga通道中分别衰减了100、30和70倍。在薄双层中，自然Ga沟道的平均猝发持续时间是厚双层中的30倍。RR二氧杂环戊烷连接的Ga二聚体在GMO/Decane中“失活”，但在含有角鲨烯的双层膜中不“激活”。在不同的Ga通道中，闪烁的平均关闭时间(∼为0.12ms)基本相同。在薄的双层膜中，gH值比厚的双层膜大10%(SS)、30%(RR)和20%(∼)(自然Ga)。结果表明，闪变与Ga单体的预解离或解离状态无关，也不是由通道蛋白的本征构象变化引起的。我们认为闪烁是由于双层膜的起伏使Ga沟道的开口消失而引起的。不同的Ga沟道中闪烁频率的差异可能是由于双层/沟道界面的沟道几何形状的变化造成的。较小的ErgHin厚双层表明，这些双层膜在Ga沟道周围的形变在沟道口附近创建了一条扩散路径，该路径比薄的GMO双层膜更长，限制更多。对这些效应尝试了一种可能的分子解释。
The submillisecond closing events (flickers) and the single channel conductances to protons (gH) were studied in native gramicidin A (gA) and in the SS and RR diastereoisomers of dioxolane-linked gA channels in planar bilayers. Bilayers were formed from glycerylmonooleate (GMO) in various solvents. In GMO/decane (thick) bilayers, the largest flicker frequency occurred in the SS channel (39s−1), followed by the RR (4s−1) and native gA channels (3s−1). These frequencies were attenuated in GMO/squalene (thin) bilayers by 100-, 30-, and 70-fold in the SS, RR, and native gA channels, respectively. In thin bilayers, the average burst duration of native gA channels was 30-fold longer than in thick bilayers. The RR dioxolane-linked gA dimer "inactivated" in GMO/decane but not in squalene-containing bilayers. The mean closed time of flickers (∼0.12ms) was essentially the same in various gA channels. In thin bilayers,gHvalues were larger by ∼10% (SS), 30% (RR), and 20% (native gA) in relation to thick bilayers. It is concluded that flickers are not related to pre-dissociation or dissociation states of gA monomers, and do not seem to be caused by intrinsic conformational changes of channel proteins. It is proposed that flickers are caused by undulations of the bilayer that obliterate the openings of gA channels. Differences between flicker frequencies in various gA channels are likely to result from variations in channel geometries at the bilayer/channel interface. The smallergHin thick bilayers suggests that the deformation of these bilayers around the gA channel creates a diffusional pathway next to the mouths of the channel that is longer and more restrictive than in thin GMO bilayers. A possible molecular interpretation for these effects is attempted.