Vergani Paola, Lockless Steve W, Nairn Angus C, Gadsby David C
Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, New York 10021, USA.
Nature. 2005 Feb 24;433(7028):876-80. doi: 10.1038/nature03313.
ABC (ATP-binding cassette) proteins constitute a large family of membrane proteins that actively transport a broad range of substrates. Cystic fibrosis transmembrane conductance regulator (CFTR), the protein dysfunctional in cystic fibrosis, is unique among ABC proteins in that its transmembrane domains comprise an ion channel. Opening and closing of the pore have been linked to ATP binding and hydrolysis at CFTR's two nucleotide-binding domains, NBD1 and NBD2 (see, for example, refs 1, 2). Isolated NBDs of prokaryotic ABC proteins dimerize upon binding ATP, and hydrolysis of the ATP causes dimer dissociation. Here, using single-channel recording methods on intact CFTR molecules, we directly follow opening and closing of the channel gates, and relate these occurrences to ATP-mediated events in the NBDs. We find that energetic coupling between two CFTR residues, expected to lie on opposite sides of its predicted NBD1-NBD2 dimer interface, changes in concert with channel gating status. The two monitored side chains are independent of each other in closed channels but become coupled as the channels open. The results directly link ATP-driven tight dimerization of CFTR's cytoplasmic nucleotide-binding domains to opening of the ion channel in the transmembrane domains. This establishes a molecular mechanism, involving dynamic restructuring of the NBD dimer interface, that is probably common to all members of the ABC protein superfamily.
ABC（ATP结合盒）蛋白构成了一个大型膜蛋白家族，可主动转运多种底物。囊性纤维化跨膜传导调节因子（CFTR）是导致囊性纤维化的功能失调蛋白，在ABC蛋白中独具特色，因为其跨膜结构域包含一个离子通道。孔道的开闭与CFTR的两个核苷酸结合结构域NBD1和NBD2处的ATP结合及水解有关（例如，参见参考文献1、2）。原核ABC蛋白的分离NBD在结合ATP时会二聚化，ATP水解会导致二聚体解离。在此，我们使用完整CFTR分子的单通道记录方法，直接跟踪通道门的开闭，并将这些事件与NBD中ATP介导的事件相关联。我们发现，预计位于其预测的NBD1-NBD2二聚体界面相对两侧的两个CFTR残基之间的能量耦合，与通道门控状态协同变化。在关闭的通道中，两个被监测的侧链相互独立，但随着通道打开而耦合。这些结果直接将CFTR胞质核苷酸结合结构域的ATP驱动紧密二聚化与跨膜结构域中离子通道的开放联系起来。这建立了一种分子机制，涉及NBD二聚体界面的动态重组，这可能是ABC蛋白超家族所有成员共有的。
