A mutation-induced activated state of the beta 2-adrenergic receptor. Extending the ternary complex model.
A mutation-induced activated state of the beta 2-adrenergic receptor. Extending the ternary complex model.
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DOI：
10.1016/s0021-9258(18)53442-6
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发表时间：
1993-03
期刊：
影响因子：
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通讯作者：
P. Samama;S. Cotecchia;T. Costa;R. Lefkowitz
中科院分区：
文献类型：
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作者：
P. Samama;S. Cotecchia;T. Costa;R. Lefkowitz
我们用α1B-肾上腺素受体的同源区域替换了β2-肾上腺素受体第三个细胞内环的C-末端部分（残基266-272）。以与之前描述的 α 1B 受体的相互突变类似的方式（Cotecchia，S.，Exum，S.，Caron，M.G.，和 Lefkowitz，R.J.（1990）Proc.Natl.Acad.Sci.U.S.A.87，2896-2900），这种保守取代导致腺苷酸环化酶的不依赖于激动剂的激活。此外，组成型活性突变受体表现出：（i）对激动剂的亲和力增加（即使不存在鸟嘌呤核苷酸结合调节蛋白（G蛋白）），但对拮抗剂则不然，亲和力增加的程度与配体的内在活性相关； (ii) 激动剂刺激腺苷酸环化酶的效力增加； (iii) 部分激动剂的内在活性增加。我们记录了我们对突变受体的实验结果不能在三元复合物模型的理论框架内充分合理化（De Lean, A., Stadel, J. M., and Lefkowitz, R. J. (1980) J. Biol. Chem. 255, 7108-7117），该模型假设受体激活需要激动剂促进形成激动剂、受体、和G蛋白。我们通过广泛的计算机模拟表明，该模型的扩展版本包括受体（R）到活性状态（R*）的显式异构化，与我们对突变型和野生型受体的所有发现密切相关。对这种组成型活性突变型 G 蛋白偶联受体的研究应有助于阐明受体激活过程的分子性质。
We have replaced the C-terminal portion of the third intracellular loop of the beta 2-adrenergic receptor (residues 266-272) with the homologous region of the alpha 1B-adrenergic receptor. In a fashion analogous to the reciprocal mutations of the alpha 1B receptor previously described (Cotecchia, S., Exum, S., Caron, M. G., and Lefkowitz, R. J. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 2896-2900), this conservative substitution leads to agonist-independent activation of adenylyl cyclase. In addition, the constitutively active mutant receptor exhibits: (i) an increased affinity for agonists (even in the absence of guanine nucleotide-binding regulatory protein (G protein)) but not antagonists, with the extent of affinity increase being correlated with the intrinsic activity of the ligand; (ii) an increased potency of agonists for stimulation of adenylyl cyclase; and (iii) an increased intrinsic activity of partial agonists. We document that our experimental findings with the mutant receptor cannot be adequately rationalized within the theoretical framework of the Ternary Complex Model (De Lean, A., Stadel, J. M., and Lefkowitz, R. J. (1980) J. Biol. Chem. 255, 7108-7117) which postulates that receptor activation requires the agonist-promoted formation of an active, “ternary” complex of agonist, receptor, and G protein. We show, through extensive computer simulations, that an extended version of this model that includes an explicit isomerization of the receptor (R) to an active state (R*) closely models all our findings for both the mutant and the wild-type receptors. Study of such constitutively active mutant G protein-coupled receptors should help elucidate the molecular nature of the processes involved in receptor activation.