Development of subtype‐selective drugs for G protein‐coupled receptors poses a significant challenge due to high similarity between subtypes, as exemplified by the three β‐adrenergic receptors (βARs). The β3AR agonists show promise for treating the overactive bladder or preterm birth, but their potential is hindered by off‐target activation of β1AR and β2AR. Interestingly, several β‐blockers, which are antagonists of the β1ARs and β2ARs, have been reported to exhibit agonist activity at the β3AR. However, the molecular mechanism remains elusive. Understanding the underlying mechanism should facilitate the development of β3AR agonist drugs with improved selectivity and reduced off‐target effects. In this work, we determined the structures of human β3AR in complex with the endogenous agonist epinephrine or with a synthetic β3AR agonist carazolol, which is also a high‐affinity β‐blocker. Structure comparison, mutagenesis studies and molecular dynamics simulations revealed that the differences on the flexibility of D3.32 directly contribute to carazolol’s distinct activities as an antagonist for the β2AR and an agonist for the β3AR. The process is also indirectly influenced by the extracellular loops (ECL), especially ECL1. Taken together, these results provide key guidance for development of selective β3AR agonists, paving the way for new therapeutic opportunities.

中文翻译：

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β-受体阻滞剂的 β3AR 激动剂活性的分子机制


由于亚型之间的高度相似性，G 蛋白偶联受体的亚型选择性药物的开发提出了重大挑战，以三种 β 肾上腺素能受体 (βAR) 为例。 β3AR 激动剂有望治疗膀胱过度活动症或早产，但其潜力因 β1AR 和 β2AR 的脱靶激活而受到阻碍。有趣的是，据报道，几种β受体阻滞剂（β1AR和β2AR的拮抗剂）对β3AR表现出激动剂活性。然而，其分子机制仍然难以捉摸。了解其潜在机制应有助于开发具有更高选择性和减少脱靶效应的 β3AR 激动剂药物。在这项工作中，我们确定了人 β3AR 与内源性激动剂肾上腺素或合成 β3AR 激动剂卡拉洛尔（也是一种高亲和力 β 受体阻滞剂）复合物的结构。结构比较、诱变研究和分子动力学模拟表明，D3.32 灵活性的差异直接导致卡拉洛尔作为 β2AR 拮抗剂和 β3AR 激动剂的独特活性。该过程还间接受到细胞外环 (ECL)，尤其是 ECL1 的影响。总而言之，这些结果为选择性 β3AR 激动剂的开发提供了关键指导，为新的治疗机会铺平了道路。