Cis-trans isomerization at a proline opens the pore of a neurotransmitter-gated ion channel
Cis-trans isomerization at a proline opens the pore of a neurotransmitter-gated ion channel
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DOI：
10.1038/nature04130
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发表时间：
2005-11-10
期刊：
影响因子：
64.8
通讯作者：
Dougherty, DA
中科院分区：
文献类型：
--
作者：
Lummis, SCR;Beene, DL;Dougherty, DA
5-羟色胺3型（5-HT 3）受体是Cys环受体超家族的成员（1）。这些蛋白质中的神经递质结合通过尚未表征的构象变化触发离子通道的打开（门控）。在这里，我们表明，一个特定的脯氨酸（Pro 8*），位于第二和第三跨膜螺旋（M2 - M3）（2，3）之间的环的顶点，可以通过蛋白质骨架的顺反异构化连接结合门控。使用非天然氨基酸诱变，一系列脯氨酸类似物的顺式构象异构体的不同偏好被纳入在8* 位置。脯氨酸类似物，强烈有利于反式构象产生非功能性通道。在功能突变体中，脯氨酸类似物的固有顺-反能隙与通道的活化之间存在强相关性，表明该单个脯氨酸的顺-反异构化提供了使通道的开放和闭合状态相互转换的开关。与这一提议一致，对M2 - M3环肽的核磁共振研究揭示了两种不同的结构形式。因此，我们的研究结果证实了M2 - M3环的结构和Pro 8* 在5-HT 3受体中的关键作用。此外，他们认为Pro 8* 的分子重排是打开受体孔的结构机制。
5-Hydroxytryptamine type 3 (5-HT3) receptors are members of the Cys-loop receptor superfamily(1). Neurotransmitter binding in these proteins triggers the opening (gating) of an ion channel by means of an as-yet-uncharacterized conformational change. Here we show that a specific proline ( Pro 8*), located at the apex of the loop between the second and third transmembrane helices (M2 - M3)(2,3), can link binding to gating through a cis-trans isomerization of the protein backbone. Using unnatural amino acid mutagenesis, a series of proline analogues with varying preference for the cis conformer was incorporated at the 8* position. Proline analogues that strongly favour the trans conformer produced nonfunctional channels. Among the functional mutants there was a strong correlation between the intrinsic cis - trans energy gap of the proline analogue and the activation of the channel, suggesting that cis - trans isomerization of this single proline provides the switch that interconverts the open and closed states of the channel. Consistent with this proposal, nuclear magnetic resonance studies on an M2 - M3 loop peptide reveal two distinct, structured forms. Our results thus confirm the structure of the M2 - M3 loop and the critical role of Pro 8* in the 5-HT3 receptor. In addition, they suggest that a molecular rearrangement at Pro 8* is the structural mechanism that opens the receptor pore.