A homology modeling study toward the understanding of three-dimensional structure and putative pharmacological profile of the G-protein coupled receptor GPR55

The orphan G-protein coupled receptor GPR55 was shown to bind to certain cannabinoid compounds which led to its initial classification as the third type of cannabinoid receptor. Later studies showed that lysophosphatidylinositol (LPI) also activated GPR55, in particular 2-arachidonoyl-LPI was proposed to be its endogenous ligand. However, the results of pharmacological studies regarding GPR55 have been quite inconsistent. Despite its contradictory pharmacological profile, GPR55 has been implicated in various disease states including inflammatory and neuropathic pain, metabolic bone diseases, and cancer. Herein, we report the ligand binding properties of GPR55 by applying homology modeling and automated docking algorithms in order to understand its pharmacological profile. The 3D homology model of GPR55 was built based on the adenosine A2A receptor crystal structure. Docking studies of several types of reported ligands were carried out afterwards. The results indicated that both hydrogen bonding and hydrophobic interactions contributed significantly for its ligand binding and the amino acid residue Lys80 seemed to be the anchor residue for receptor recognition. In addition, its putative agonist and antagonist appeared to recognize different domains of the receptor corresponding to their reported pharmacological activities.

Graphical abstractGPR55 antagonist CBD binding mode in the GPR55 homology model.Figure optionsDownload full-size imageDownload high-quality image (175 K)Download as PowerPoint slideHighlight► We constructed the homology model of the orphan G-protein coupled receptor GPR55. ► A number of reported ligands were docked into the homology model of the receptor. ► Ligand binding sites were characterized and analyzed. ► Critical anchor amino acid residue was identified. ► Putative agonist and antagonist binding pockets were discussed.