Nearly a hundred different KCNQ1 mutations have been reported as leading to the cardiac long QT syndrome, characterized by prolonged QT interval, syncopes, and sudden death. We have previously shown that phosphatidylinositol-4,5-bisphosphate (PIP2) regulates the KCNQ1-KCNE1 complex. In the present study, we show that PIP2 affinity is reduced in three KCNQ1 mutant channels (R243H, R539W, and R555C) associated with the long QT syndrome. In giant excised patches, direct application of PIP2 on the cytoplasmic face of the three mutant channels counterbalances the loss of function. Reintroduction of a positive charge by application of methanethiosulfonate ethylammonium on the cytoplasmic face of R555C mutant channels also restores channel activity. The channel affinity for a soluble analog of PIP2 is decreased in the three mutant channels. By using a model that describes the KCNQ1-KCNE1 channel behavior and by fitting the relationship between the kinetics of deactivation and the current amplitude obtained in whole-cell experiments, we estimated the PIP2 binding and dissociation rates on wild-type and mutant channels. The dissociation rate of the three mutants was higher than for the wild-type channel, suggesting a decreased affinity for PIP2. PIP2 binding was magnesium-dependent, and the PIP2-dependent equilibrium constant in the absence of magnesium was higher with the wild-type than with the mutant channels. Altogether, our data suggest that a reduced PIP2 affinity of KCNQ1 mutants can lead to the long QT syndrome.

中文翻译：

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受损的KCNQ1-KCNE1和磷脂酰肌醇-4,5-双磷酸酯相互作用是长期QT综合征的基础。

据报道，将近一百种不同的KCNQ1突变导致心脏长QT综合征，其特征是QT间隔时间延长，晕厥和猝死。先前我们已经表明磷脂酰肌醇-4,5-双磷酸酯（PIP2）调节KCNQ1-KCNE1复合物。在本研究中，我们显示与长QT综合征相关的三个KCNQ1突变通道（R243H，R539W和R555C）中的PIP2亲和力降低。在巨大的切除斑块中，将PIP2直接应用在三个突变通道的细胞质面上可抵消功能丧失。通过在R555C突变体通道的细胞质表面上应用甲硫代磺酸盐乙铵重新引入正电荷，也可以恢复通道活性。在三个突变体通道中降低了对PIP2可溶性类似物的通道亲和力。通过使用描述KCNQ1-KCNE1通道行为的模型，并拟合失活动力学与全细胞实验中获得的电流幅度之间的关系，我们估计了野生型和突变型通道上PIP2的结合和解离速率。这三个突变体的解离速率高于野生型通道，表明对PIP2的亲和力降低。PIP2结合是镁依赖性的，并且在不存在镁的情况下，野生型的PIP2依赖性平衡常数高于突变型通道。总而言之，我们的数据表明KCNQ1突变体的PIP2亲和力降低会导致长时间的QT综合征。