G protein-coupled receptors (GPCRs) are membrane proteins constituting the largest family of drug targets. The activated GPCR binds either the heterotrimeric G proteins or arrestin through its activation cycle. Water molecules have been reported to play a role in GPCR activation. Nevertheless, reported studies are focused on the hydrophobic helical bundle region. How water molecules function in GPCR bound either G protein or arrestin is rarely studied. To address this issue, we carried out computational studies on water molecules in both GPCR/G protein complexes and GPCR/arrestin complexes. Using inhomogeneous fluid theory (IFT), we locate all possible hydration sites in GPCRs binding either to G protein or arrestin. We observe that the number of water molecules on the interaction surface between GPCRs and signal proteins are correlated with the insertion depths of the α5-helix from G-protein or “finger loop” from arrestin in GPCRs. In three out of the four simulation pairs, the interfaces of Rhodopsin, M₂R and NTSR1 in the G protein-associated systems show more water-mediated hydrogen-bond networks when compared to these in arrestin-associated systems. This reflects that more functionally relevant water molecules may probably be attracted in G protein-associated structures than that in arrestin-associated structures. Moreover, we find the water-mediated interaction networks throughout the NPxxY region and the orthosteric pocket, which may be a key for GPCR activation. Reported studies show that non-biased agonist, which can trigger both GPCR-G protein and GPCR-arrestin activation signal, can result in pharmacologically toxicities. Our comprehensive studies of the hydration sites in GPCR/G protein complexes and GPCR/arrestin complexes may provide important insights in the design of G-protein biased agonists.

G 蛋白偶联受体 (GPCR) 是构成最大的药物靶标家族的膜蛋白。激活的 GPCR 通过其激活周期结合异三聚体 G 蛋白或抑制蛋白。据报道，水分子在 GPCR 激活中发挥作用。然而，报道的研究集中在疏水螺旋束区域。很少研究水分子如何在 GPCR 中发挥作用，结合 G 蛋白或抑制蛋白。为了解决这个问题，我们对 GPCR/G 蛋白复合物和 GPCR/arrestin 复合物中的水分子进行了计算研究。使用不均匀流体理论 (IFT)，我们定位了 GPCR 中所有可能的水合位点，这些位点与 G 蛋白或抑制蛋白结合。我们观察到 GPCR 和信号蛋白之间相互作用表面上的水分子数量与 G 蛋白的 α5-螺旋或 GPCR 中抑制蛋白的“指环”插入深度相关。在四个模拟对中的三个中，视紫红质的界面，M_{与抑制蛋白相关系统中的相比，G 蛋白相关系统中的2} R 和 NTSR1 显示出更多的水介导氢键网络。这反映出与抑制蛋白相关结构相比，更多功能相关的水分子可能被吸引到 G 蛋白相关结构中。此外，我们发现整个 NPxxY 区域和正构口袋中都有水介导的相互作用网络，这可能是 GPCR 激活的关键。报道的研究表明，可触发 GPCR-G 蛋白和 GPCR-arrestin 激活信号的非偏向激动剂可导致药理学毒性。我们对 GPCR/G 蛋白复合物和 GPCR/抑制蛋白复合物中水合位点的全面研究可能为 G 蛋白偏向激动剂的设计提供重要见解。