Waldmann R, Champigny G, Lazdunski M
Institut de Pharmacologie Moléculaire et Cellulaire, Sophia Antipolis, Valbonne, France.
J Biol Chem. 1995 May 19;270(20):11735-7. doi: 10.1074/jbc.270.20.11735.
The highly selective, amiloride-sensitive Na+ channel is formed of three homologous subunits termed alpha, beta, and gamma. The three subunits exhibit similarities with Caenorhabditis elegans proteins called degenerins involved in sensory touch transduction and, when mutated, in neurodegeneration. Swelling of neurons observed in neurodegeneration suggests an involvement of ion transport, but the channel function of degenerins has not yet been demonstrated. We used chimeras to study the functional relationship between the epithelial sodium channel and the degenerin Mec-4. Exchange of the hydrophobic domains of the Na+ channel alpha subunit by those of Mec-4 results in a functional ion channel with changed pharmacology for amiloride and benzamil and changed selectivity, conductance, gating, and voltage dependence. All of these differences were also obtained by exchanging Ser-589 and Ser-593 in the second transmembrane region by the corresponding residues of Mec-4, suggesting that these two residues are essential for the ionic pore function of the channel.
高度选择性的、对氨氯地平敏感的钠离子通道由三个同源亚基组成，分别称为α、β和γ。这三个亚基与秀丽隐杆线虫中参与感觉触觉转导的蛋白（称为退化蛋白）具有相似性，并且在发生突变时会参与神经退行性变。在神经退行性变中观察到的神经元肿胀表明离子转运参与其中，但退化蛋白的通道功能尚未得到证实。我们使用嵌合体来研究上皮钠通道与退化蛋白Mec-4之间的功能关系。用Mec-4的疏水结构域替换钠离子通道α亚基的疏水结构域，会产生一个功能离子通道，其对氨氯地平和苄amil的药理学特性发生改变，选择性、电导率、门控和电压依赖性也发生改变。通过用Mec-4的相应残基替换第二跨膜区的Ser-589和Ser-593，也获得了所有这些差异，这表明这两个残基对于通道的离子孔功能至关重要。
