A speed limit for conformational change of an allosteric membrane protein
A speed limit for conformational change of an allosteric membrane protein
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DOI：
10.1073/pnas.0406777102
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发表时间：
2005-01-04
影响因子：
11.1
通讯作者：
Auerbach, A
中科院分区：
文献类型：
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作者：
Chakrapani, S;Auerbach, A
神经肌肉乙酰胆碱受体是突触离子通道，其打开和关闭的速率常数分别约为48，000 s（-1）和1，700 s-1（成年小鼠，24 ℃，-100 mV膜电位）。蛋白质中许多不同位点的扰动可以改变这些速率常数，其中细胞外结构域中的那些主要影响通道开放，而膜和细胞内结构域中的许多那些主要影响通道关闭。我们使用单通道记录来测量由低浓度的天然递质乙酰胆碱引起的每次激活的总开放时间（tau（B））。tau（B）在具有突变的构建体中增加，所述突变通过增加打开速率常数或降低关闭速率常数来增加门控平衡常数。然而，tau（B）在快速打开和缓慢关闭构建体中没有接近相同的渐近线。缓慢关闭器的最大值大约是快速开启器的两倍。对这种差异的一种解释是，通道开放速率常数有一个上限，我们估计约为0.86 μ s（-1）。一种可能性是，这个限制是在没有整体激活障碍的情况下的构象变化率，从而反映了乙酰胆碱受体开放异构化的动力学前因子。
Neuromuscular acetylcholine receptors are synaptic ion channels that open and close with rate constants of approximate to48,000 s(-1) and approximate to1,700 s-1, respectively (in adult mouse, at 24degreesC, -100 mV membrane potential). Perturbations of many different sites in the protein can change these rate constants, with those in the extracellular domain mainly affecting channel-opening and many of those in the membrane and intracellular domains mainly affecting channel-closing. We used single-channel recordings to measure the total open time per activation (tau(b)) elicited by a low concentration of the natural transmitter, acetylcholine. tau(b) increased in constructs with mutations that increased the gating equilibrium constant by either increasing the opening or decreasing the closing rate constant. However, tau(b) did not approach the same asymptote in fast-opening and slow-closing constructs. The maximum value for the slow closers was about twice that for the fast openers. One interpretation of this difference is that there is an upper limit to the channel-opening rate constant, which we estimate to be approximate to0.86 mus(-1). One possibility is that this limit is the rate of conformational change in the absence of an overall activation barrier and thus reflects the kinetic prefactor for the acetylcholine receptor opening isomerization.