Root M J, MacKinnon R
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Neuron. 1993 Sep;11(3):459-66. doi: 10.1016/0896-6273(93)90150-p.
Divalent cation blockade of cGMP-gated channels in photoreceptor cells ensures the low open channel noise required for a highly sensitive visual transduction process. This study identifies a divalent cation-binding site in the pore of a retinal cGMP-gated channel expressed in Xenopus oocytes. Substitution of a specific glutamate residue by a neutral amino acid renders the channel insensitive to external Mg2+ and Ca2+ and affects the conduction of Na+. The mutated channels remain sensitive to internal divalent cations. These results place the glutamate residue in the ion conduction pathway close to the extracellular surface.
光感受器细胞中cGMP门控通道的二价阳离子阻断确保了高灵敏度视觉转导过程所需的低开放通道噪声。本研究在非洲爪蟾卵母细胞中表达的视网膜cGMP门控通道的孔中鉴定出一个二价阳离子结合位点。用中性氨基酸取代特定的谷氨酸残基会使通道对外部Mg2+和Ca2+不敏感，并影响Na+的传导。突变后的通道对内部二价阳离子仍敏感。这些结果表明谷氨酸残基位于靠近细胞外表面的离子传导途径中。
