Cryo-EM Structures of the Human 5-HT_2BR Bound to Three Distinct Ligands Reveal Molecular Determinants of Subtype...

The 5-HT_2BR, a member of the G protein-coupled receptor (GPCR) family, has been implicated in various diseases, including cardiovascular conditions, fibrotic disorders, cancer, and neuropsychiatric illnesses. Despite its therapeutic potential, the 5-HT_2BR remains largely underexplored due to the limited availability of subtype-selective ligands. Additionally, many drugs either exhibit off-target binding to 5-HT_2BR or fail to achieve specificity for their intended receptor subtype. Here, we present three cryo-electron microscopy structures of the human 5-HT_2BR in complex with the antagonist tegaserod, the inverse agonist ritanserin, and the selective antagonist RS127445, respectively. These structures reveal distinct binding modes for each ligand, and through detailed analysis, we identify residues L362 and V366 as key contributors to 5-HT₂ subtype selectivity, while E363 and the ECL2 region play critical roles in 5-HT_2BR subtype selectivity. Our findings offer valuable insights into the molecular mechanisms behind ligand selectivity for 5-HT_2BR, laying the groundwork for the development of 5-HT_2BR-selective ligands.