Adams C M, Snyder P M, Price M P, Welsh M J
Howard Hughes Medical Institute, Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
J Biol Chem. 1998 Nov 13;273(46):30204-7. doi: 10.1074/jbc.273.46.30204.
BNC1 is a mammalian neuronal cation channel in the novel DEG/ENaC ion channel family. BNC1 channels are transiently activated by extracellular protons and are constitutively activated by insertion of large residues, such as valine, in place of Gly-430; residue 430 is a site where analogous mutations in some Caenorhabditis elegans family members cause a swelling neurodegeneration. Mutation of Gly-430 to a small amino acid, cysteine, neither generated constitutive currents nor allowed modification of this residue by sulfhydryl-reactive methanethiosulfonate (MTS) compounds. However, when protons activated the channel, Cys-430 became accessible to extracellular MTS reagents, which modified Cys-430 to generate constitutive currents. Fluorescent MTS reagents also labeled Cys-430 in activated channels. These data indicate that protons induce a reversible conformational change that activates BNC1 thereby exposing residue 430 to the extracellular solution. Once Cys-430 is modified with a large chemical group, the channel is prevented from relaxing back to the inactive state. These results link ligand-dependent activation and activation by mutations that cause neurodegeneration.
BNC1是新型DEG/ENaC离子通道家族中的一种哺乳动物神经元阳离子通道。BNC1通道可被细胞外质子短暂激活，并通过插入大的残基（如缬氨酸）取代甘氨酸430而持续激活；残基430是秀丽隐杆线虫一些家族成员中类似突变导致肿胀性神经变性的位点。将甘氨酸430突变为小氨基酸半胱氨酸，既不会产生持续电流，也不允许巯基反应性甲硫基磺酸盐（MTS）化合物对该残基进行修饰。然而，当质子激活通道时，半胱氨酸430可被细胞外MTS试剂作用，这些试剂修饰半胱氨酸430以产生持续电流。荧光MTS试剂也标记激活通道中的半胱氨酸430。这些数据表明，质子诱导可逆的构象变化从而激活BNC1，进而使残基430暴露于细胞外溶液中。一旦半胱氨酸430被大的化学基团修饰，通道就会被阻止恢复到非活性状态。这些结果将配体依赖性激活与导致神经变性的突变激活联系起来。
