Robert Lefkowitz, at Duke University, began in the 1970s a research program that identified and isolated G protein-coupled receptors (GPCRs), a family of cell-membrane proteins that allows cells to detect external signals — hormones, neurotransmitters, light, smells, tastes — and translate them into internal responses. Lefkowitz uses radioactive isotopes to label hormones and locate their receptors on the cell membrane, identifying the beta-adrenergic receptor as the first characterized member of the family. Brian Kobilka, who joined Lefkowitz's lab in the 1980s, clones the gene for the beta-adrenergic receptor in 1986 and discovers that its sequence is strikingly similar to that of rhodopsin — the eye's light receptor — revealing that both belong to the same evolutionary family of proteins with seven transmembrane helices. In 2011, Kobilka succeeds in crystallizing the beta-adrenergic receptor at the exact moment of activation by a hormone, capturing for the first time the three-dimensional structure of a GPCR in the act of signaling. Around 800 distinct GPCRs have been identified in the human genome, regulating functions ranging from vision and smell to cardiovascular and mood regulation. Approximately one-third of all drugs currently in clinical use — including beta-blockers, antihistamines, and antipsychotics — act on some GPCR, making this receptor family the most exploited pharmacological target in modern medicine.