Phe-308 and Phe-312 in transmembrane domain 7 are major sites of alpha 1-adrenergic receptor antagonist binding. Imidazoline agonists bind like antagonists.
Phe-308 and Phe-312 in transmembrane domain 7 are major sites of alpha 1-adrenergic receptor antagonist binding. Imidazoline agonists bind like antagonists.
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DOI：
10.1074/jbc.m103152200
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发表时间：
2001-07
期刊：
影响因子：
--
通讯作者：
D. Waugh;R. Gaivin;M. Zuscik;P. Gonzalez-Cabrera;S. Ross;J. Yun;D. Perez
中科院分区：
文献类型：
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作者：
D. Waugh;R. Gaivin;M. Zuscik;P. Gonzalez-Cabrera;S. Ross;J. Yun;D. Perez
尽管肾上腺素能受体中的激动剂结合是相当好理解的，并且涉及位于跨膜结构域3至6中的残基，但报道的参与拮抗剂结合的残基很少。事实上，在任何G蛋白偶联受体中从未报道过拮抗剂的主要对接位点。据推测，根据拮抗剂的化学结构，拮抗剂结合是相当多样的，这可能与激动剂完全不同。我们现在报告了在α（1a）-肾上腺素能受体跨膜结构域7中鉴定出两个苯丙氨酸残基（Phe-312和Phe-308），它们是拮抗剂亲和力的主要位点。Phe-308或Phe-312的突变导致对拮抗剂哌唑嗪、WB 4101、BMY 7378、（+）尼古地平和5-甲基乌拉地尔的亲和力显著丧失（4-1200倍），而对苯乙胺类激动剂（如肾上腺素、甲氧胺或苯肾上腺素）的亲和力无变化。有趣的是，这两个残基参与所有咪唑啉型激动剂如羟甲唑啉、环唑啉和可乐定的结合，证实了先前的证据，即这类配体的结合不同于苯乙胺型激动剂，并且可能更像拮抗剂，这可以解释它们的部分激动剂性质。在建模这些相互作用与以前的诱变研究，并使用目前的骨干结构的视紫红质，我们得出结论，拮抗剂结合对接更高的口袋更接近细胞外表面比激动剂结合，并出现偏向跨膜结构域7。
Although agonist binding in adrenergic receptors is fairly well understood and involves residues located in transmembrane domains 3 through 6, there are few residues reported that are involved in antagonist binding. In fact, a major docking site for antagonists has never been reported in any G-protein coupled receptor. It has been speculated that antagonist binding is quite diverse depending upon the chemical structure of the antagonist, which can be quite different from agonists. We now report the identification of two phenylalanine residues in transmembrane domain 7 of the alpha(1a)-adrenergic receptor (Phe-312 and Phe-308) that are a major site of antagonist affinity. Mutation of either Phe-308 or Phe-312 resulted in significant losses of affinity (4-1200-fold) for the antagonists prazosin, WB4101, BMY7378, (+) niguldipine, and 5-methylurapidil, with no changes in affinity for phenethylamine-type agonists such as epinephrine, methoxamine, or phenylephrine. Interestingly, both residues are involved in the binding of all imidazoline-type agonists such as oxymetazoline, cirazoline, and clonidine, confirming previous evidence that this class of ligand binds differently than phenethylamine-type agonists and may be more antagonist-like, which may explain their partial agonist properties. In modeling these interactions with previous mutagenesis studies and using the current backbone structure of rhodopsin, we conclude that antagonist binding is docked higher in the pocket closer to the extracellular surface than agonist binding and appears skewed toward transmembrane domain 7.