Transport of maltodextrins through maltoporin: A single-channel study
Transport of maltodextrins through maltoporin: A single-channel study
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DOI：
10.1016/s0006-3495(02)75442-8
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发表时间：
2002-02-01
影响因子：
3.4
通讯作者：
Bezrukov, SM
中科院分区：
文献类型：
--
作者：
Kullman, L;Winterhalter, M;Bezrukov, SM
糖通过重组成平面类脂膜的麦芽糖通道的运输传统上是使用多通道制剂来解决的。在这里，我们展示了单通道实验提供了新的可能性来揭示糖和通道之间相互作用的分子细节。我们分析了在不同大小的麦芽糊精存在的情况下，麦芽多林离子电流的时间分辨瞬时中断。我们发现，对于所有被研究的糖，从麦芽三糖到麦芽七糖，只需要一个糖分子就可以完全阻断麦芽三聚体中的一个毛孔。不同毛孔同时堵塞的概率随着糖浓度的增加而增加，这表明它们相互独立。麦芽糖通道是不对称的，并且仅从一侧加入，主要以定向的方式插入。渠道结构的不对称性以两种方式表现出来。首先，它被认为是在其他对称条件下对施加电压的不对称反应；其次，由于糖的不对称(单侧)添加，糖进入通道的速率不对称。重要的是，我们发现糖在毛孔中的停留时间并不取决于糖被添加到哪一边。对于对称、顺式或反式糖加成，这一电压依赖时间是相同的。这一观察表明，一旦糖分子被通道的“油腻滑道”捕获，它就会在那里停留足够长的时间，以至于“忘记”它是从哪个入口捕获的。这也意味着，这里研究的阻断事件代表了糖的转运事件，而不仅仅是在通道的同一入口处结合和释放。
Transport of sugars through maltoporin channels reconstituted into planar lipid membranes has traditionally been addressed using multichannel preparations. Here we show that single-channel experiments offer new possibilities to reveal molecular details of the interaction between the sugar and the channel. We analyze time-resolved transient interruptions in the maltoporin ionic current in the presence of differently sized maltodextrins. We find for all studied sugars, from maltotriose to maltoheptaose, that only one sugar molecule is required to completely block one of the pores in the maltoporin trimer. The probability of simultaneous blockage of different pores increases with sugar concentration in a manner that demonstrates their mutual independence. The maltoporin channel is asymmetric and, added from one side only, predominantly inserts in an oriented manner. The asymmetry of the channel structure manifests itself in two ways. First, it is seen as an asymmetrical response to applied voltage at otherwise symmetrical conditions; second, as asymmetrical rates of sugar entry into the channel with asymmetrical (one-sided) sugar addition. Importantly, we find that the sugar residence time in the pore does not depend on which side the sugar is added. This voltage-dependent time is the same for symmetrical, cis, or trans sugar addition. This observation suggests that once a sugar molecule is captured by the "greasy slide" of the channel, it spends enough time there to "forget" from what entrance it was captured. This also means that the blockage events studied here represent sugar translocation events, and not just binding at and release from the same entrance of the channel.