Department of Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Biochim Biophys Acta Biomembr. 2021 Apr 1;1863(4):183558. doi: 10.1016/j.bbamem.2021.183558. Epub 2021 Jan 11.
Mutations at many sites within the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel pore region result in changes in chloride conductance. Although chloride binding in the pore - as well as interactions between concurrently bound chloride ions - are thought to be important facets of the chloride permeation mechanism, little is known about the relationship between anion binding and chloride conductance. The present work presents a comprehensive investigation of a number of anion binding properties in different pore mutants with differential effects on chloride conductance. When multiple pore mutants are compared, conductance appears best correlated with the ability of anions to bind to the pore when it is already occupied by chloride ions. In contrast, conductance was not correlated with biophysical measures of anion:anion interactions inside the pore. Although these findings suggest anion binding is required for high conductance, mutations that strengthened anion binding had very little effect on conductance, especially at high chloride concentrations, suggesting that the wild-type CFTR pore is already close to saturated with chloride ions. These results are used to support a revised model of chloride permeation in CFTR in which the overall chloride occupancy of multiple loosely-defined chloride binding sites results in high chloride conductance through the pore.
囊性纤维化跨膜电导调节因子 (CFTR) 氯离子通道孔区的许多位置的突变导致氯离子电导率发生变化。尽管孔内氯离子结合以及同时结合的氯离子之间的相互作用被认为是氯离子渗透机制的重要方面，但关于阴离子结合与氯离子电导率之间的关系知之甚少。本工作全面研究了对氯离子电导率有不同影响的多种孔突变体的一些阴离子结合特性。当比较多个孔突变体时，电导率似乎与阴离子在已经被氯离子占据的孔中结合的能力密切相关。相比之下，电导率与阴离子在孔内的阴离子：阴离子相互作用的生物物理测量值无关。尽管这些发现表明阴离子结合对于高电导率是必需的，但增强阴离子结合的突变对电导率几乎没有影响，尤其是在高氯离子浓度下，这表明野生型 CFTR 孔已经接近氯离子饱和。这些结果用于支持 CFTR 中氯离子渗透的修正模型，其中多个定义不明确的氯离子结合位点的总体氯离子占有率导致氯离子通过孔的高电导率。
