Cloning of a gamma-aminobutyric acid type C receptor subunit in rat retina with a methionine residue critical for picrotoxinin channel block.
Cloning of a gamma-aminobutyric acid type C receptor subunit in rat retina with a methionine residue critical for picrotoxinin channel block.
复制标题
在大鼠视网膜中克隆 γ-氨基丁酸 C 型受体亚基，其蛋氨酸残基对印防己毒素通道阻断至关重要。
DOI：
10.1073/pnas.92.25.11756
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发表时间：
1995
影响因子：
11.1
通讯作者：
Lipton,SA
中科院分区：
文献类型：
--
作者：
Zhang,D;Pan,ZH;Zhang,X;Brideau,AD;Lipton,SA
γ -氨基丁酸（GABA）的嗜离子受体在抑制哺乳动物视网膜的神经传递中起重要作用，介导GABAA和GABAC反应。在许多物种中，这些反应被惊厥性微旋毒素（PTX）阻断，尽管阻断的机制尚不完全清楚。相比之下，大鼠视网膜中的GABAC反应对PTX具有极强的抵抗力。我们假设这种差异可以通过GABAC反应背后受体的分子特征来解释。在这里，我们报道了两个大鼠GABA受体亚基的克隆，命名为r rho 1和r rho 2在他们之前鉴定的人类同源物。当在爪蟾卵母细胞中共表达时，r rho 1/r rho 2异质受体模拟了大鼠视网膜的ptx抗性GABAC反应。由于同质受体r rho 1对PTX敏感，PTX抗性显然是由天然异质受体r rho 2亚基赋予的；单独的rho 2亚基不能形成功能性的同质受体。位点定向诱变证实，第二跨膜区域的一个氨基酸残基（r rho 2中的一个蛋氨酸取代r rho 1中的一个苏氨酸）是大鼠受体PTX抗性的主要决定因素。这项研究不仅揭示了PTX阻断GABA受体的分子机制，还揭示了PTX抵抗GABAC反应的大鼠视网膜中天然受体的异质性。
Ionotropic receptors for gamma-aminobutyric acid (GABA) are important to inhibitory neurotransmission in the mammalian retina, mediating GABAA and GABAC responses. In many species, these responses are blocked by the convulsant picrotoxinin (PTX), although the mechanism of block is not fully understood. In contrast, GABAC responses in the rat retina are extremely resistant to PTX. We hypothesized that this difference could be explained by molecular characterization of the receptors underlying the GABAC response. Here we report the cloning of two rat GABA receptor subunits, designated r rho 1 and r rho 2 after their previously identified human homologues. When coexpressed in Xenopus oocytes, r rho 1/r rho 2 heteromeric receptors mimicked PTX-resistant GABAC responses of the rat retina. PTX resistance is apparently conferred in native heteromeric receptors by r rho 2 subunits since homomeric r rho 1 receptors were sensitive to PTX; r rho 2 subunits alone were unable to form functional homomeric receptors. Site-directed mutagenesis confirmed that a single amino acid residue in the second membrane-spanning region (a methionine in r rho 2 in place of a threonine in r rho 1) is the predominant determinant of PTX resistance in the rat receptor. This study reveals not only the molecular mechanism underlying PTX blockade of GABA receptors but also the heteromeric nature of native receptors in the rat retina that underlie the PTX-resistant GABAC response.