CHANNELS FORMED BY COLICIN-E1 IN PLANAR LIPID BILAYERS ARE LARGE AND EXHIBIT PH-DEPENDENT ION SELECTIVITY
CHANNELS FORMED BY COLICIN-E1 IN PLANAR LIPID BILAYERS ARE LARGE AND EXHIBIT PH-DEPENDENT ION SELECTIVITY
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DOI：
10.1007/bf01872215
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发表时间：
1985-01-01
影响因子：
2.4
通讯作者：
FINKELSTEIN, A
中科院分区：
文献类型：
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作者：
RAYMOND, L;SLATIN, SL;FINKELSTEIN, A
E1亚组(E1、A、Ib等)已知的一种称为结肠素的抗菌毒素在平面脂质双层中形成电压依赖的通道。粘附素E1、A和Ib的基因已经被克隆和测序，这使得这些通道成为细胞通道中普遍存在的电压依赖现象的有趣模型。研究了与模型建立相关的离子选择性和通道大小。显然，粘菌素E1通道很大，最窄处的直径至少为8A。这是通过测量由大阳离子或大阴离子的盐形成的梯度的反转电势而建立的。在这样做的过程中，利用了结肠素通道对阳离子和阴离子均可渗透的事实；它对它们的相对选择性是pH的函数。在中性膜中，该通道具有阴离子选择性(氯离子优先于K+)；选择性程度高度依赖于pH。在带负电的膜中，当pH‘’S高于约5时，它成为阳离子选择性。跨膜的pH梯度实验表明，通道管腔内和通道末端附近的可滴定基团都会影响选择性。单独的E1通道都有>；1开放电导状态，都表现出类似的离子选择性。Colicins A和Ib也表现出依赖于pH的离子选择性，并且似乎比E1的管腔更大。
The E1 subgroup (E1, A, Ib, etc.) of antibacterial toxins called colicins are known to form voltage-dependent channels in planar lipid bilayers. The genes for colicins E1, A and Ib have been cloned and sequenced, making these channels interesting models for the widespread phenomenon of voltage dependence in cellular channels. Ion selectivity and channel size.sbd.properties relevant to model building were investigated. Apparently, the colicin E1 channel is large, having a diameter of at least 8 A at its narrowest point. This was established from measurements of reversal potentials for gradients formed by salts of large cations or large anions. In so doing, the fact that the colicin channel is permeable to both cations and anions was exploited; its relative selectivity to them is a function of pH. The channel is anion selective (Cl over K+) in neutral membranes; the degree of selectivity is highly dependent on pH. In negatively charged membranes, it becomes cation selective at pH''s higher than about 5. Experiments with pH gradients cross the membrane suggest that titratable groups both within the channel lumen and near the channel ends affect the selectivity. Individual E1 channels have > 1 open conductance state, all displaying comparable ion selectivity. Colicins A and Ib also exhibit pH-dependent ion selectivity, and appear to have even larger lumens than E1.