Molecular insights into the modulation of the 5HT2A receptor by serotonin, psilocin, and the G protein subunit Gqalpha

The 5HT2A receptor (5HT2AR) is a G protein-coupled receptor that drives many neuronal functions and is one of the primary targets for psychedelic drugs, which have recently shown promise in treating mental disorders. Understanding ligand interactions and conformational transitions is essential for developing effective pharmaceuticals, but mechanistic details of 5HT2AR activation and ligand binding modes remain poorly understood. We conducted all-atom molecular dynamics simulations and free energy calculations of the active and inactive forms of 5HT2AR with psilocin and serotonin. Both serotonin and psilocin have higher binding affinities for the orthosteric binding pocket than the extended binding pocket. Active state 5HT2AR collapses to a closed state in the absence of Gq. We also discover a partially-open receptor conformation that is intermediate between the active and inactive states. Our discoveries can inform the design of new pharmaceuticals that target specific receptor conformations, potentially leading to more effective treatments for mental disorders.