Department of Psychiatry, University of California, San Francisco, CA 94158, USA.
Sci Signal. 2011 Aug 9;4(185):ra52. doi: 10.1126/scisignal.2001748.
In comparison to endogenous ligands of seven-transmembrane receptors, which typically act as full agonists, many drugs act as partial agonists. Partial agonism is best described as a "macroscopic" property that is manifest at the level of physiological systems or cell populations; however, whether partial agonists also encode discrete regulatory information at the "microscopic" level of individual receptors is not known. Here, we addressed this question by focusing on morphine, a partial agonist drug for μ-type opioid peptide receptors (MORs), and by combining quantitative mass spectrometry with cell biological analysis to investigate the reduced efficacy of morphine, compared to that of a peptide full agonist, in promoting receptor endocytosis. We showed that these chemically distinct ligands produced a complex and qualitatively similar mixture of phosphorylated opioid receptor forms in intact cells. Quantitatively, however, the different agonists promoted disproportionate multisite phosphorylation of a specific serine and threonine motif, and we found that modification at more than one residue was essential for the efficient recruitment of the adaptor protein β-arrestin that mediated subsequent endocytosis of MORs. Thus, quantitative encoding of agonist-selective endocytosis at the level of individual opioid receptors was based on the conserved biochemical principles of multisite phosphorylation and threshold detection.
与通常作为完全激动剂的七跨膜受体的内源性配体相比，许多药物作为部分激动剂起作用。部分激动作用最好被描述为一种“宏观”特性，在生理系统或细胞群体水平上表现出来；然而，部分激动剂是否也在单个受体的“微观”水平上编码离散的调节信息尚不清楚。在这里，我们通过关注吗啡（μ 型阿片肽受体（MOR）的部分激动剂药物）来解决这个问题，并通过结合定量质谱和细胞生物学分析来研究与肽完全激动剂相比，吗啡促进受体内吞的效力降低的问题。我们表明，这些化学性质不同的配体在完整细胞中产生了复杂的、定性相似的阿片受体磷酸化形式混合物。然而，定量地，不同的激动剂促进了特定丝氨酸和苏氨酸模体的不成比例的多部位磷酸化，并且我们发现，多于一个残基的修饰对于介导随后的 MOR 内吞作用的衔接蛋白β-arrestin 的有效募集是必不可少的。因此，在单个阿片受体水平上，激动剂选择性内吞的定量编码基于多部位磷酸化和阈值检测的保守生化原理。
