GPCR-targeting antibodies are increasingly important. Structurally aided maturation of GPCR-antibody interactions can enhance target engagement and reveal receptor conformational changes associated with antibody binding [1]. Cryo-electron microscopy (cryo-EM) is the preferred method for elucidating GPCR structures, including both agonist-bound active states and, increasingly, antagonist-bound inactive states [2]. Furthermore, cryo-EM provides an excellent tool for epitope mapping of GPCR-targeted antibodies. However, obtaining high-quality GPCR samples for antibody discovery and cryo-EM structure determination is challenging due to the inherent size, flexibility, and instability of GPCRs post-extraction from the membrane [3]. Effective strategies and critical decisions in construct design, expression, and purification are essential for producing high-quality samples to be used as immunogens and for successful imaging. We present a new cryo-EM structure of the 5-HT2A receptor, demonstrating scFv16 binding at its epitope and revealing a novel serotonin binding conformation.<\/p>\n