Department of Physiology & Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
J Membr Biol. 2023 Dec;256(4-6):433-442. doi: 10.1007/s00232-023-00294-w. Epub 2023 Oct 12.
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. Structural analysis of CFTR has identified a narrow, hydrophobic region close to the extracellular end of the open channel pore that may function as a selectivity filter. The present study combines comprehensive mutagenesis of hydrophobic amino-acid side-chains within the selectivity filter with functional evaluation of channel Cl conductance and anion selectivity. Among these hydrophobic amino-acids, one (F337) appears to play a dominant role in determining both conductance and selectivity. Anion selectivity appears to depend on both side-chain size and hydrophobicity at this position. In contrast, conductance is disrupted by all F337 mutations, suggesting that unique interactions between permeating Cl ions and the native phenylalanine side-chain are important for conductance. Surprisingly, a positively charged lysine side-chain can be substituted for several hydrophobic residues within the selectivity filter (including F337) with only minor changes in pore function, arguing against a crucial role for overall hydrophobicity. These results suggest that localized interactions between permeating anions and amino-acid side-chains within the selectivity filter may be more important in determining pore functional properties than are global features such as overall hydrophobicity.
囊性纤维化是由囊性纤维化跨膜电导调节因子（CFTR）阴离子通道中的突变引起的。CFTR 的结构分析确定了靠近开放通道孔的细胞外端的狭窄疏水区，该区域可能作为选择性过滤器发挥作用。本研究结合了对选择性过滤器中疏水性氨基酸侧链的综合诱变与通道 Cl 电导和阴离子选择性的功能评估。在这些疏水性氨基酸中，一个（F337）似乎在确定电导和选择性方面都起着主导作用。阴离子选择性似乎取决于该位置的侧链大小和疏水性。相比之下，所有 F337 突变都会破坏电导，这表明穿透 Cl 离子与天然苯丙氨酸侧链之间的独特相互作用对于电导很重要。令人惊讶的是，带正电荷的赖氨酸侧链可以取代选择性过滤器中的几个疏水性残基（包括 F337），而对孔功能的影响很小，这表明总体疏水性的作用不大。这些结果表明，在确定孔功能特性方面，穿透阴离子与选择性过滤器中氨基酸侧链之间的局部相互作用可能比整体特征（如总体疏水性）更为重要。
