Pluhackova Kristyna, Wilhelm Florian M, Müller Daniel J
Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zurich, Basel, Switzerland.
Front Cell Dev Biol. 2021 Dec 23;9:807913. doi: 10.3389/fcell.2021.807913. eCollection 2021.
G protein-coupled receptors (GPCRs) are the largest class of human membrane proteins that bind extracellular ligands at their orthosteric binding pocket to transmit signals to the cell interior. Ligand binding evokes conformational changes in GPCRs that trigger the binding of intracellular interaction partners (G proteins, G protein kinases, and arrestins), which initiate diverse cellular responses. It has become increasingly evident that the preference of a GPCR for a certain intracellular interaction partner is modulated by a diverse range of factors, e.g., ligands or lipids embedding the transmembrane receptor. Here, by means of molecular dynamics simulations of the β-adrenergic receptor and β-arrestin2, we study how membrane lipids and receptor phosphorylation regulate GPCR-arrestin complex conformation and dynamics. We find that phosphorylation drives the receptor's intracellular loop 3 (ICL3) away from a native negatively charged membrane surface to interact with arrestin. If the receptor is embedded in a neutral membrane, the phosphorylated ICL3 attaches to the membrane surface, which widely opens the receptor core. This opening, which is similar to the opening in the G protein-bound state, weakens the binding of arrestin. The loss of binding specificity is manifested by shallower arrestin insertion into the receptor core and higher dynamics of the receptor-arrestin complex. Our results show that receptor phosphorylation and the local membrane composition cooperatively fine-tune GPCR-mediated signal transduction. Moreover, the results suggest that deeper understanding of complex GPCR regulation mechanisms is necessary to discover novel pathways of pharmacological intervention.
G蛋白偶联受体（GPCRs）是人类最大的一类膜蛋白，它们在其正构结合口袋处结合细胞外配体，以将信号传递到细胞内部。配体结合会引发GPCRs的构象变化，从而触发细胞内相互作用伙伴（G蛋白、G蛋白激酶和阻遏蛋白）的结合，进而引发各种细胞反应。越来越明显的是，GPCR对特定细胞内相互作用伙伴的偏好受到多种因素的调节，例如嵌入跨膜受体的配体或脂质。在这里，通过对β-肾上腺素能受体和β-阻遏蛋白2进行分子动力学模拟，我们研究了膜脂和受体磷酸化如何调节GPCR-阻遏蛋白复合物的构象和动力学。我们发现，磷酸化会驱使受体的细胞内环3（ICL3）远离带负电荷的天然膜表面，从而与阻遏蛋白相互作用。如果受体嵌入中性膜中，磷酸化的ICL3会附着在膜表面，这会使受体核心广泛打开。这种类似于G蛋白结合状态下的打开方式会削弱阻遏蛋白的结合。结合特异性的丧失表现为阻遏蛋白插入受体核心变浅以及受体-阻遏蛋白复合物的动力学增加。我们的结果表明，受体磷酸化和局部膜组成协同微调GPCR介导的信号转导。此外，结果表明，深入了解复杂的GPCR调节机制对于发现新的药理干预途径是必要的。
