Ligands Raise the Constraint That Limits Constitutive Activation in G Protein-coupled Opioid Receptors
Ligands Raise the Constraint That Limits Constitutive Activation in G Protein-coupled Opioid Receptors
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DOI：
10.1074/jbc.m113.474452
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发表时间：
2013-08-16
影响因子：
4.8
通讯作者：
Costa, Tommaso
中科院分区：
文献类型：
--
作者：
Vezzi, Vanessa;Onaran, H. Ongun;Costa, Tommaso
利用无细胞生物发光共振能量转移策略，我们比较了delta （DOP）和mu （MOP）阿片受体中自发和配体诱导的受体- g蛋白偶联的水平。在这个实验中，GDP可以抑制自发偶联，从而允许其量化。DOP的组成活性水平是MOP受体的4-5倍。一系列阿片类药物类似物与一个共同的拟肽支架显示出显著的功效反转在两个受体。增强MOP受体低固有水平以上偶联的激动剂在降低较高水平的DOP受体组成偶联方面是反向激动剂。然而，这两种配体的内在活性在两种受体的GDP基线上是相同的。这种模式与三元复模型和“两态”扩展的预测相冲突。根据这一理论，如果在活性和非活性形式之间的平衡转移引起一种受体类型的本构激活，则自发和配体诱导偶联的顺序不能逆转。我们提出本构激活是由于抑制自发耦合的内在屏障减弱。任何配体，无论其功效如何，都必须增强这种约束以稳定配体结合的络合形式。
Using a cell-free bioluminescence resonance energy transfer strategy we compared the levels of spontaneous and ligand-induced receptor-G protein coupling in delta (DOP) and mu (MOP) opioid receptors. In this assay GDP can suppress spontaneous coupling, thus allowing its quantification. The level of constitutive activity was 4-5 times greater at the DOP than at the MOP receptor. A series of opioid analogues with a common peptidomimetic scaffold displayed remarkable inversions of efficacy in the two receptors. Agonists that enhanced coupling above the low intrinsic level of the MOP receptor were inverse agonists in reducing the greater level of constitutive coupling of the DOP receptor. Yet the intrinsic activities of such ligands are identical when scaled over the GDP base line of both receptors. This pattern is in conflict with the predictions of the ternary complex model and the "two state" extensions. According to this theory, the order of spontaneous and ligand-induced coupling cannot be reversed if a shift of the equilibrium between active and inactive forms raises constitutive activation in one receptor type. We propose that constitutive activation results from a lessened intrinsic barrier that restrains spontaneous coupling. Any ligand, regardless of its efficacy, must enhance this constraint to stabilize the ligand-bound complexed form.