Pore-forming transmembrane domains control ion selectivity and selectivity filter conformation in the KirBac1.1 potassium channel.
Pore-forming transmembrane domains control ion selectivity and selectivity filter conformation in the KirBac1.1 potassium channel.
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DOI：
10.1085/jgp.202012683
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发表时间：
2021-05-03
期刊：
影响因子：
--
通讯作者：
Nichols CG
中科院分区：
文献类型：
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作者：
Matamoros M;Nichols CG
Matamoros和Nichols表明，KirBac1.1 K+通道选择性过滤器外的跨膜结构域的突变会影响离子传输，这表明通道选择性是由不同结构域之间的物理相互作用决定的。钾离子通道是一种膜蛋白，具有选择性传导钾离子的能力。高分辨率结构表明，脱水的K+离子通过签名选择性过滤器（SF）序列TxGYG的主链羰基形成的最窄的孔区渗透。然而，具有类似SF序列的非选择性通道的存在，以及其他区域突变对选择性的影响，表明SF不是选择性的唯一决定因素。我们通过在跨膜螺旋2 （TM2）的残基I131上引入突变，改变了KirBac1.1通道的选择性。这些突变在没有K+的情况下增加了Na+通量，并引入了显著的质子电导。与K+通道晶体结构一致，单分子FRET实验表明，SF在高K+条件下是构象约束和稳定的，但在高na +/低K+条件下会过渡到膨胀的低FRET状态。与野生型通道相比，I131M突变体的SF动态对K+和Na+的依赖性明显转变为高K+和低Na+浓度。这些结果阐明了I131以及潜在的SF外的其他结构元素在控制离子选择性中的作用，表明这些元素与SF的物理相互作用有助于约束K+诱导的SF构型与非选择性扩张构象的相对稳定性。
Matamoros and Nichols show that mutations in a transmembrane domain outside of the selectivity filter of the KirBac1.1 K+ channel affect ion transport, suggesting that channel selectivity is determined by the physical interaction between different domains. Potassium (K+) channels are membrane proteins with the remarkable ability to very selectively conduct K+ ions across the membrane. High-resolution structures have revealed that dehydrated K+ ions permeate through the narrowest region of the pore, formed by the backbone carbonyls of the signature selectivity filter (SF) sequence TxGYG. However, the existence of nonselective channels with similar SF sequences, as well as effects of mutations in other regions on selectivity, suggest that the SF is not the sole determinant of selectivity. We changed the selectivity of the KirBac1.1 channel by introducing mutations at residue I131 in transmembrane helix 2 (TM2). These mutations increase Na+ flux in the absence of K+ and introduce significant proton conductance. Consistent with K+ channel crystal structures, single-molecule FRET experiments show that the SF is conformationally constrained and stable in high-K+ conditions but undergoes transitions to dilated low-FRET states in high-Na+/low-K+ conditions. Relative to wild-type channels, I131M mutants exhibit marked shifts in the K+ and Na+ dependence of SF dynamics to higher K+ and lower Na+ concentrations. These results illuminate the role of I131, and potentially other structural elements outside the SF, in controlling ion selectivity, by suggesting that the physical interaction of these elements with the SF contributes to the relative stability of the constrained K+-induced SF configuration versus nonselective dilated conformations.
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