Relationship between nucleotide binding and ion channel gating in cystic fibrosis transmembrane conductance regulator
Relationship between nucleotide binding and ion channel gating in cystic fibrosis transmembrane conductance regulator
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DOI：
10.1113/jphysiol.2009.170258
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发表时间：
2009-06-15
影响因子：
5.5
通讯作者：
Riordan, John R.
中科院分区：
文献类型：
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作者：
Aleksandrov, Andrei A.;Cui, Liying;Riordan, John R.
我们采用速率-平衡自由能关系（REFER）分析来表征囊性纤维化跨膜传导调节因子（CFTR）功能的变构调节中所涉及的动态事件。广泛的不同的水解和难水解的核苷三磷酸被用来阐明ATP水解在CFTR功能中的作用。REFER图的线性和所有测试配体的接近1的Phi值意味着CFTR通道门控是可逆的热驱动过程，其中结合位点中的所有结构重组在通道开放之前完成。这与核苷酸结合用于通道开放的要求一致。然而，从开放状态到闭合状态的通道结构转变独立于结合位点中的任何事件而发生。在蛋白质的相对两半中的核苷酸结合结构域（NBD）和细胞质环（CL）之间的偶联接头处的氨基酸取代上获得了类似的结果，表明在通道闭合状态下也发生了任何结构重组。在这些遥远的站点中的任一个中未观察到分数Phi值的事实表明，在核苷酸结合位点和通道门之间可能没有确定性的"臂“机制起作用。这些发现有利于结合和门控之间的随机耦合，其中所有的结构转变都是热驱动的过程。我们推测，通道开放状态概率的增加是由于配体结合NBD和通道之间的物理相互作用后，可用的闭合状态配置的数量减少。
We have employed rate-equilibrium free energy relationship (REFER) analysis to characterize the dynamic events involved in the allosteric regulation of cystic fibrosis transmembrane conductance regulator (CFTR) function. A wide range of different hydrolysable and poorly hydrolysable nucleoside triphosphates were used to elucidate the role of ATP hydrolysis in CFTR function. The linearity of the REFER plots and Phi values near unity for all ligands tested implies that CFTR channel gating is a reversible thermally driven process with all structural reorganization in the binding site(s) completed prior to channel opening. This is consistent with the requirement for nucleotide binding for channel opening. However, the channel structural transition from the open to the closed state occurs independently of any events in the binding sites. Similar results were obtained on substitution of amino acids at coupling joints between both nucleotide binding domains (NBD) and cytoplasmic loops (CL) in opposite halves of the protein, indicating that any structural reorganization there also had occurred in the channel closed state. The fact that fractional Phi values were not observed in either of these distant sites suggests that there may not be a deterministic 'lever-arm' mechanism acting between nucleotide binding sites and the channel gate. These findings favour a stochastic coupling between binding and gating in which all structural transitions are thermally driven processes. We speculate that increase of channel open state probability is due to reduction of the number of the closed state configurations available after physical interaction between ligand bound NBDs and the channel.