Cystic Fibrosis Transmembrane Conductance Regulator: A Molecular Model Defines the Architecture of the Anion Conduction Path and Locates a 鈥淏ottleneck鈥?in the Pore

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• 作者：Yohei Norimatsu ; Anthony Ivetac ; Christopher Alexander ; John Kirkham ; Nicolette O鈥橠onnell ; David C. Dawson ; Mark S. P. Sansom
• 刊名：Biochemistry
• 出版年：2012
• 出版时间：March 20, 2012
• 年：2012
• 卷：51
• 期：11
• 页码：2199-2212
• 全文大小：735K
• 年卷期：v.51,no.11(March 20, 2012)
• ISSN：1520-4995

文摘

We developed molecular models for the cystic fibrosis transmembrane conductance regulator chloride channel based on the prokaryotic ABC transporter, Sav1866. Here we analyze predicted pore geometry and side-chain orientations for TM3, TM6, TM9, and TM12, with particular attention being paid to the location of the rate-limiting barrier for anion conduction. Side-chain orientations assayed by cysteine scanning were found to be from 77 to 90% in accord with model predictions. The predicted geometry of the anion conduction path was defined by a space-filling model of the pore and confirmed by visualizing the distribution of water molecules from a molecular dynamics simulation. The pore shape is that of an asymmetric hourglass, comprising a shallow outward-facing vestibule that tapers rapidly toward a narrow 鈥渂ottleneck鈥?linking the outer vestibule to a large inner cavity extending toward the cytoplasmic extent of the lipid bilayer. The junction between the outer vestibule and the bottleneck features an outward-facing rim marked by T338 in TM6 and I1131 in TM12, consistent with the observation that cysteines at both of these locations reacted with both channel-permeant and channel-impermeant, thiol-directed reagents. Conversely, cysteines substituted for S341 in TM6 or T1134 in TM12, predicted by the model to lie below the rim of the bottleneck, were found to react exclusively with channel-permeant reagents applied from the extracellular side. The predicted dimensions of the bottleneck are consistent with the demonstrated permeation of Cl^{鈥?/sup>, pseudohalide anions, water, and urea.}