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hERG为延迟整流钾电流快成分 (Ikr)的基因 ,hERG通道在S5跨膜片段和孔区之间有一长的细胞外环 ,大约 39个氨基酸 ,这一细胞外S5 P环的点位突变与遗传性长QT(LQT2 )综合征有密切联系。因此 ,这一区域在决定hERG通道功能方面具有非常重要的意义。应用先进的分子生物学方法将这一区域的两个组氨酸残基 (H5 78和H5 87)突变为脯氨酸 (P) ,利用青蛙卵母细胞这一表达系统将wild type和突变的hERG通道表达于该细胞膜 ,通过膜片钳技术来探讨点突变与通道功能改变之间的关系 ,实验研究表明在 5 78位置的组氨酸 (H1)突变并不影响HERG通道功能 ,然而 ,在 5 87位置的组氨酸 (H2 )突变就可破坏该通道的C -型灭活过程和孔的K+ 选择性 ,通道激活的电压依赖性也向超极化侧移动 ,这一现象说明 ,hERG通道细胞外侧S5 -P环围绕 5 87位置肽段骨架的构象变化能够影响该通道的门控特性和离子选择性功能。因此 ,该研究揭示了HERG通道S5 P环的 5 87位置突变和LQT2Ikr功能丧失之间有着密切联系。
hERG is the gene for the delayed rectifier potassium current component (Ikr), which has a long extracellular loop of approximately 39 amino acids between the S5 transmembrane segment and the pore region. This site-directed mutagenesis of the extracellular S5P loop is associated with Hereditary long QT (LQT2) syndrome are closely linked. Therefore, this region is of great importance in determining the function of hERG channels. The two histidine residues (H578 and H5 87) in this region were mutated to proline (P) using advanced molecular biology methods. Using the expression system of frog oocytes, wild type and mutant hERG channels are expressed on the cell membrane and the relationship between point mutations and channel function changes is explored by patch clamp techniques. Experimental studies show that the histidine (H1) mutation at position 578 does not affect HERG channel function, however, The 5-position mutation of histidine (H2) abolished the C-type inactivation of the channel and the K + selectivity of the pore, and the voltage-dependent activation of the channel also shifted to the hyperpolarized side, indicating that hERG Conformational changes of the peptide backbone around the S570-loop in the extracellular compartment of the channel can affect the gating and ion-selective functions of this channel. Therefore, this study revealed a close relationship between the 5 87 position mutation in the R5P loop of the HERG channel and the loss of LQT2Ikr function.