Mutation-induced transformations of conductivity and selectivity in NaChBac bacterial channels are studied experimentally and interpreted within the framework of ionic Coulomb blockade (ICB), while also taking account of resonant quantised dehydration (QD) and site protonation. Site-directed mutagenesis and whole-cell patch-clamp experiments are used to investigate how the fixed charge Qf at the selectivity filter (SF) affects both valence selectivity and same-charge selectivity. The new ICB/QD model predicts that increasing ∣Qf∣ should lead to a shift in selectivity sequences toward larger ion sizes, in agreement with the present experiments and with earlier work. Comparison of the model with experimental data leads to the introduction of an effective charge Qf∗ at the SF, which was found to differ between Aspartate and Glutamate charged rings, and also to depend on position within the SF. It is suggested that protonation of the residues within the restricted space of the SF is important in significantly reducing the effective charge of the EEEE ring. Values of Qf∗ derived from experiments on divalent blockade agree well with expectations based on the ICB/QD model and have led to the first demonstration of ICB oscillations in Ca2+ conduction as a function of the fixed charge. Preliminary studies of the dependence of Ca2+ conduction on pH are qualitatively consistent with the predictions of the model.

中文翻译：

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离子库仑阻滞剂和NaChBac细菌钠通道选择性的决定因素。

对NaChBac细菌通道中电导率和选择性的突变诱导的转化进行了实验研究，并在离子库仑阻滞（ICB）的框架内进行了解释，同时还考虑了共振定量脱水（QD）和位点质子化。定点诱变和全细胞膜片钳实验用于研究选择性过滤器（SF）上的固定电荷Qf如何影响价键选择性和等电荷选择性。新的ICB / QD模型预测，与当前实验和早期工作一致，增加的Qff会导致选择性序列向更大的离子尺寸转移。将模型与实验数据进行比较后，在SF处引入了有效电荷Qf ∗，这在天冬氨酸和谷氨酸盐带电环之间有所不同，并且还取决于SF中的位置。有人认为，SF受限空间内的残基质子化对于显着降低EEEE环的有效电荷很重要。从二价阻滞实验得出的Qf ∗值与基于ICB / QD模型的预期非常吻合，并首次证明了Ca2 +传导中的ICB振荡是固定电荷的函数。Ca2 +传导对pH的依赖性的初步研究在质量上与模型的预测一致。从二价阻滞实验得出的Qf ∗值与基于ICB / QD模型的预期非常吻合，并首次证明了Ca2 +传导中的ICB振荡是固定电荷的函数。Ca2 +传导对pH的依赖性的初步研究在质量上与模型的预测一致。从二价阻滞实验得出的Qf *值与基于ICB / QD模型的预期非常吻合，并首次证明了Ca2 +传导中的ICB振荡是固定电荷的函数。Ca2 +传导对pH的依赖性的初步研究在质量上与模型的预测一致。