On a small table in his office at the Scripps Research Institute in La Jolla, California, Ray Stevens spreads out a sheet of paper covered with colourful branched lines, each sprouting and thinning before terminating in an esoteric code. “This is the dream,” he declares.
The intricate diagram represents the largest family of receptor proteins encoded in the genome — the G-protein-coupled receptors (GPCRs), ubiquitous cell-surface molecules that are activated by light, odours, hormones and neurotransmitters. Stevens wants to determine the atomic structures of receptors on all branches of the tree. This week, that goal moved two receptors closer: Stevens’s group has solved the atomic structure of the κ-opioid receptor (κ-OR)1, and a team led by Brian Kobilka at Stanford University in California has solved the medically crucial μ-opioid receptor (μ-OR)2. The structures, published in Nature, bring the tally of GPCR structures solved this year alone up to five.