Identification of natural products as novel ligands for the human 5-HT_2C receptor

G protein-coupled receptors (GPCRs) constitute the largest human protein family with over 800 members, which are implicated in many important medical conditions. Serotonin receptors belong to the aminergic GPCR subfamily and play important roles in physiological and psychological activities. Structural biology studies have revealed the structures of many GPCRs in atomic details and provide the basis for the identification and investigation of the potential ligands, which interact with and modulate the receptors. Here, an integrative approach combining a focused target-specific natural compound library, a thermal-shift-based screening method, affinity mass spectrometry, molecular docking, and in vitro as well as in vivo functional assay, was applied to identify (-)-crebanine and several other aporphine alkaloids as initial hits for a human serotonin receptor subtype, the 5-HT_2C receptor. Further studies illuminated key features of their binding affinity, downstream signaling and tissue reaction, providing a molecular explanation for the interaction between (-)-crebanine and human 5-HT_2C receptor.