Deciphering the Molecular Association of Human CRIP1a with an Agonist-Bound Cannabinoid Receptor 1

Cannabinoid receptor 1 (CB1) is a class A G-protein-coupled receptor that plays important roles in several physiological and pathophysiological processes. Therefore, targeted regulation of CB1 activity is a potential therapeutic strategy for several diseases, including neurological disorders. Apart from cannabinoid ligands, CB1 signaling can also be regulated by different CB1-associated proteins. In particular, the cannabinoid receptor interacting protein 1a (CRIP1a) associates with an activated CB1 receptor and alters the G-protein selectivity, thereby reducing the agonist-mediated signal transduction of the CB1 receptor. Experimental evidence suggests that two peptides corresponding to the distal and central C-terminal segments of CB1 could interact with CRIP1a. However, our knowledge of the molecular basis of CB1-CRIP1a recognition is still limited. In this work, we use an extensive combination of computational methods to build the first comprehensive atomistic model human CB1-CRIP1a complex. Our model provides novel structural insights into the interactions of CRIP1a with a membrane-embedded, complete, agonist-bound CB1 receptor in humans. Our results highlight the key residues that stabilize the CB1-CRIP1a complex, which will be useful to guide in vitro mutagenesis experiments. Furthermore, our human CB1-CRIP1a complex presents a model system for structure-based drug design to target this physiologically important complex for modulating CB1 activity.大麻素受体1（Cannabinoid receptor 1, CB1）是一类A类G蛋白偶联受体（class A G-protein-coupled receptor），在诸多生理及病理生理过程中发挥关键作用。因此，对CB1活性进行靶向调控，是包括神经系统疾病在内的多种疾病的潜在治疗策略。除大麻素配体（cannabinoid ligands）外，CB1信号通路还可通过不同的CB1相关蛋白（CB1-associated proteins）进行调控。其中，大麻素受体相互作用蛋白1a（Cannabinoid receptor interacting protein 1a, CRIP1a）可与激活态CB1受体（activated CB1 receptor）结合，并改变其G蛋白选择性（G-protein selectivity），进而削弱激动剂介导的CB1受体信号转导（agonist-mediated signal transduction）。已有实验证据表明，对应于CB1远端及中央C端结构域（distal and central C-terminal segments）的两段肽段可与CRIP1a相互作用，但目前学界对CB1与CRIP1a识别的分子基础仍知之甚少。本研究通过全面整合的多种计算方法，构建了首个全面的全原子人类CB1-CRIP1a复合物模型。该模型为解析CRIP1a与膜嵌入型、完整且结合激动剂的人类CB1受体之间的相互作用提供了全新的结构视角。本研究结果明确了稳定CB1-CRIP1a复合物的关键残基，可为后续体外诱变实验（in vitro mutagenesis experiments）提供指导。此外，本研究构建的人类CB1-CRIP1a复合物可作为基于结构的药物设计（structure-based drug design）模型系统，用于靶向调控这一具有重要生理意义的复合物，以调节CB1活性。