Computational Investigation of Functional Water Molecules Upon GPCR Bound to G protein or Arrestin

Abstract

G protein-coupled receptors (GPCRs) are membrane proteins, which constitutes the largest family of drug targets. The activated GPCR can bound either G protein or Arrestin to accomplish its activation. Water molecules were reported to play an intriguing role in GPCR activation. Nevertheless, reported studies are focused in the hydrophobic helical bundle region. How water molecules function upon 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 the inhomogeneous fluid theory (IFT), hydration sites of GPCRs in G protein or Arrestin binding state were located and their functions were comprehensively analyzed. In the interaction surface of GPCR-G protein/Arrestin, a lot of water molecules were found. In addition, we found that the number of water molecules on the interaction surface of GPCR-G protein/Arrestin system is highly associated with the insertion depth of the α5-helix and “Finger Loop”. We observed that water molecules near the interaction surface of GPCR-G protein/Arrestin exhibit great differences. Most G protein-related structures attract more function water molecules than Arrestin-associated structures. The G protein-related GPCRs show more potent binding water molecules and water-mediated hydrogen-bond compared to Arrestin complexes. Moreover, a small amount of water molecules is observed in the NPxxY region, while a large number of water molecules are in the orthosteric pocket and form rich interaction networks. Our results provide a comprehensive and deep understanding on the hydration sites in GPCRs and may have important implications for GPCR-targeted drug design with functional selectivity.