Revisiting the serotonin binding pose of the 5-HT2A receptor with cryo-EM

Cryo-electron microscopy (cryo-EM) has emerged as the preferred technique for elucidating GPCR structures, encompassing both agonist-bound active states and, increasingly, antagonist-bound inactive states. Effective strategies and critical decision points for projects aimed at acquiring cryo-EM structures of GPCR complexes to facilitate drug discovery efforts will be discussed. Obtaining inactive-state cryo-EM structures can be particularly challenging due to the inherent size, flexibility, and instability of receptors when in isolation. We will share practical insights and methodologies essential for successful imaging.

We will showcase a newly obtained cryo-EM structure of the 5-HT2A receptor, which discloses a previously unprecedented serotonin binding conformation. Contrasting with earlier X-ray crystallography findings, this structure presents a binding pose of serotonin that aligns more closely with its expected behaviour. In this case, elucidation of the complete complex via cryo-EM appears to be crucial, as otherwise the prior crystallographic data provides a misleading starting point for subsequent small molecule development.