Influence of pore residues on permeation properties in the Kv2.1 potassium channel. Evidence for a selective functional interaction of K+ with the outer vestibule.
Influence of pore residues on permeation properties in the Kv2.1 potassium channel. Evidence for a selective functional interaction of K+ with the outer vestibule.
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DOI：
10.1085/jgp.20028756
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发表时间：
2003-02
期刊：
影响因子：
--
通讯作者：
Korn SJ
中科院分区：
文献类型：
--
作者：
Consiglio JF;Andalib P;Korn SJ
Kv2.1钾通道在外前庭(位置356)含有赖氨酸，显著降低开放通道对外部[K+]变化的敏感性。为了研究这种效应的机制，我们研究了这种外前庭赖氨酸对K+和Na+渗透的三个指标的影响。通透性比的测量、与选择性过滤器相互作用所需的最低[K+]的测量以及宏观K+和Na+电导的测量都符合相同的结论：Kv2.1中的前庭外区赖氨酸干扰了K+进入或离开选择性过滤器细胞外侧的能力。与其对K+渗透性能的影响不同，Lys 356对Na+渗透没有影响。这表明，Lys 356通过干扰K+选择性结合位点来限制K+的流动。结合渗透研究，选择性过滤器外部入口附近的额外诱变结果表明，该位置位于选择性过滤器的外部，并且独立于选择性过滤器。Kv1.5钾通道中同一外部前庭位置的自然产生的组氨酸的质子化对K+的渗透特性也有类似的影响。综上所述，这些结果表明，在电压门控K+通道的外前庭中存在一个选择性的、功能性的K+结合部位(例如，局部能量最小)。根据对KCSA的结构研究，我们推测该部位是K+水合/脱水的场所。最后，356位的中和增强了外向K+电流的幅度，但不影响内部K+进入孔道的能力。这些数据表明，在Kv2.1中，限制外向电流大小的是选择性过滤器中K+的退出，而不是内部K+进入通道。我们讨论了这些发现与不同K+通道中通道电导的结构基础有关的含义。
The Kv2.1 potassium channel contains a lysine in the outer vestibule (position 356) that markedly reduces open channel sensitivity to changes in external [K+]. To investigate the mechanism underlying this effect, we examined the influence of this outer vestibule lysine on three measures of K+ and Na+ permeation. Permeability ratio measurements, measurements of the lowest [K+] required for interaction with the selectivity filter, and measurements of macroscopic K+ and Na+ conductance, were all consistent with the same conclusion: that the outer vestibule lysine in Kv2.1 interferes with the ability of K+ to enter or exit the extracellular side of the selectivity filter. In contrast to its influence on K+ permeation properties, Lys 356 appeared to be without effect on Na+ permeation. This suggests that Lys 356 limited K+ flux by interfering with a selective K+ binding site. Combined with permeation studies, results from additional mutagenesis near the external entrance to the selectivity filter indicated that this site was located external to, and independent from, the selectivity filter. Protonation of a naturally occurring histidine in the same outer vestibule location in the Kv1.5 potassium channel produced similar effects on K+ permeation properties. Together, these results indicate that a selective, functional K+ binding site (e.g., local energy minimum) exists in the outer vestibule of voltage-gated K+ channels. We suggest that this site is the location of K+ hydration/dehydration postulated to exist based on the structural studies of KcsA. Finally, neutralization of position 356 enhanced outward K+ current magnitude, but did not influence the ability of internal K+ to enter the pore. These data indicate that in Kv2.1, exit of K+ from the selectivity filter, rather than entry of internal K+ into the channel, limits outward current magnitude. We discuss the implications of these findings in relation to the structural basis of channel conductance in different K+ channels.
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