Sanduo Zheng Laboratory, National Institute of Biological Sciences, Beijing 102206, China.
Department of Biochemistry and Molecular biology, Graduate School of Peking Union Medical College, Beijing 100730, China.
Proc Natl Acad Sci U S A. 2022 May 24;119(21):e2121465119. doi: 10.1073/pnas.2121465119. Epub 2022 May 20.
Galanin is a biologically active neuropeptide, and functions through three distinct G protein–coupled receptors (GPCRs), namely GALR1, GALR2, and GALR3. GALR signaling plays important roles in regulating various physiological processes such as energy metabolism, neuropathic pain, epileptic activity, and sleep homeostasis. GALR1 and GALR3 signal through the Gi/o pathway, whereas GALR2 signals mainly through the Gq/11 pathway. However, the molecular basis for galanin recognition and G protein selectivity of GALRs remains poorly understood. Here, we report the cryoelectron microscopy structures of the GALR1-Go and the GALR2-Gq complexes bound to the endogenous ligand galanin or spexin. The galanin peptide mainly adopts an alpha helical structure, which binds at the extracellular vestibule of the receptors, nearly parallel to the membrane plane without penetrating deeply into the receptor core. Structural analysis combined with functional studies reveals important structural determinants for the G protein selectivity of GALRs as well as other class A GPCRs. In addition, we show that the zinc ion is a negative allosteric regulator of GALR1 but not GALR2. Our studies provide insight into the mechanisms of G protein selectivity of GPCRs and highlight a potential function of the neuromodulator zinc ion as a modulator of GPCR signaling in the central nervous system.
甘丙肽是一种具有生物活性的神经肽，通过三种不同的 G 蛋白偶联受体（GPCRs）发挥作用，即 GALR1、GALR2 和 GALR3。GALR 信号在调节各种生理过程中发挥着重要作用，如能量代谢、神经病理性疼痛、癫痫活动和睡眠稳态。GALR1 和 GALR3 通过 Gi/o 途径信号转导，而 GALR2 主要通过 Gq/11 途径信号转导。然而，甘丙肽识别和 G 蛋白选择性的分子基础仍然知之甚少。在这里，我们报告了与内源性配体甘丙肽或 Spexin 结合的 GALR1-Go 和 GALR2-Gq 复合物的冷冻电子显微镜结构。甘丙肽肽主要采用α螺旋结构，结合在受体的细胞外前庭，几乎与膜平面平行，而不深入受体核心。结构分析结合功能研究揭示了 GALRs 以及其他 A 类 GPCRs 的 G 蛋白选择性的重要结构决定因素。此外，我们表明锌离子是 GALR1 的负变构调节剂，但不是 GALR2 的调节剂。我们的研究提供了对 GPCR 中 G 蛋白选择性机制的深入了解，并强调了神经调质锌离子作为中枢神经系统中 GPCR 信号的调节剂的潜在功能。
