A network of conserved intramolecular contacts defines the off-state of the transmembrane switch mechanism in a seven-transmembrane receptor
A network of conserved intramolecular contacts defines the off-state of the transmembrane switch mechanism in a seven-transmembrane receptor
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DOI：
10.1074/jbc.275.8.5682
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发表时间：
2000-02-25
影响因子：
4.8
通讯作者：
Hulme, EC
中科院分区：
文献类型：
--
作者：
Lu, ZL;Hulme, EC
视紫红质样7 - 跨膜（7 - TM）受体的激活需要将稳定失活状态的螺旋间约束转换为激活状态下的一组新的接触，激活状态下的受体可结合同源G蛋白。驱动这一过程的自由能由激动剂结合提供，激动剂对激活构象的亲和力高于对失活构象的亲和力。我们以M - 1型毒蕈碱乙酰胆碱受体为模型，寻找特定的螺旋间约束接触。跨膜结构域3、6和7中特定氨基酸组的组氨酸替代产生了高亲和力的Zn2 +结合位点，表明它们的侧链在失活状态下紧密相邻。丙氨酸点替代显示了削弱单个分子内接触的效果。在每种情况下，乙酰胆碱亲和力都增加了，这意味着激活状态得到了促进。这些氨基酸在整个7 - TM受体超家族中高度保守。我们提出，它们构成了一个保守的螺旋间接触网络的重要部分，该网络定义了一种通用跨膜转换机制的关闭状态。
Activation of the rhodopsin-like 7-transmembrane (7-TM) receptors requires switching interhelical constraints that stabilize the inactive state to a new set of contacts in the activated state, which binds the cognate G-protein. The free energy to drive this is provided by agonist binding, which has higher affinity to the active than to the inactive conformation. We have sought specific interhelical constraint contacts, using the M-1, muscarinic acetylcholine receptor as a model. Histidine substitutions of particular groups of amino acids, in transmembrane domains 3, 6, and 7, created high-affinity Zn2+ binding sites, demonstrating the close proximity of their side chains in the inactive state. Alanine point substitutions have shown the effect of weakening the individual intramolecular contacts. In each case, the acetylcholine affinity was increased, implying promotion of the activated state. These amino acids are highly conserved throughout the 7-TM receptor superfamily We propose that they form an important part of a network Of conserved interhelical contacts that defines the off-state of a general transmembrane switch mechanism.