Fig. 1.

A flowchart of ligand-based receptor capture and the synthesis of probe 1. (A) To initiate ligand-based receptor capture, the probe is first coupled to the ligand of interest (top of scheme) or a control ligand (glycine, bottom of scheme), after which the adduct is added to cells potentially expressing a target receptor. After an appropriate incubation time, during which the ligand binds the receptor, cells are washed to rinse away unbound probe. Cells are then exposed to UV light to activate the diazirine moiety which captures the receptor. Cells are lysed, and lysates are added to streptavidin beads. Captured proteins are digested on the beads with trypsin, and released peptides are analyzed using mass spectrometry. Comparison between the proteins identified for ligand-treated and glycine-treated cells should reveal the ligand-binding receptor. (B) Synthesis of probe 1. HBTU, hexafluorophosphate benzotriazole tetramethyl uronium.