The Na-activated K channel K1.1, encoded by the gene, is an important regulator of neuronal excitability. How intracellular Na ions bind and increase channel activity is not well understood. Analysis of K1.1 channel structures indicate that there is a large twisting of the βN-αQ loop in the intracellular RCK2 domain between the inactive and Na-activated conformations, with a lysine (K885, human subunit numbering) close enough to potentially form a salt bridge with an aspartate (D839) in βL in the Na-activated state. Concurrently, an aspartate (D884) adjacent in the same loop adopts a position within a pocket formed by the βO strand. In carrying out mutagenesis and electrophysiology with human K1.1, we found that alanine substitution of selected residues in these regions resulted in almost negligible currents in the presence of up to 40 mM intracellular Na. The exception was D884A, which resulted in constitutively active channels in both the presence and absence of intracellular Na. Further mutagenesis of this site revealed an amino acid size-dependent effect. Substitutions at this site by an amino acid smaller than aspartate (D884V) also yielded constitutively active K1.1, and D884I had Na dependence similar to wild-type K1.1, while increasing the side-chain size larger than aspartate (D884E or D884F) yielded channels that could not be activated by up to 40 mM intracellular Na. We conclude that Na binding results in a conformational change that accommodates D884 in the βO pocket, which triggers further conformational changes in the RCK domains and channel activation.

中文翻译：

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RCK2 中的分子开关触发 KNa1.1 (KCNT1) 钾通道的钠依赖性激活

由该基因编码的 Na 激活 K 通道 K1.1 是神经元兴奋性的重要调节因子。细胞内钠离子如何结合并增加通道活性尚不清楚。对 K1.1 通道结构的分析表明，细胞内 RCK2 结构域中的 βN-αQ 环在非活性构象和 Na 激活构象之间存在较大扭曲，赖氨酸（K885，人类亚基编号）足够接近，有可能形成在 Na 激活状态下，βL 中与天冬氨酸 (D839) 形成盐桥。同时，同一环中相邻的天冬氨酸 (D884) 占据由 βO 链形成的口袋内的位置。在用人 K1.1 进行诱变和电生理学时，我们发现这些区域中选定残基的丙氨酸取代导致在细胞内 Na 浓度高达 40 mM 的情况下几乎可以忽略不计的电流。 D884A 是个例外，它在细胞内 Na 存在和不存在的情况下都会导致通道持续活跃。该位点的进一步诱变揭示了氨基酸大小依赖性效应。在此位点被小于天冬氨酸 (D884V) 的氨基酸取代也产生了组成型活性 K1.1，D884I 具有与野生型 K1.1 相似的 Na 依赖性，同时增加了比天冬氨酸更大的侧链大小（D884E 或 D884F） ）产生的通道无法被高达 40 mM 的细胞内 Na 激活。我们得出结论，Na 结合导致构象变化，使 D884 容纳在 βO 口袋中，从而触发 RCK 结构域和通道激活的进一步构象变化。