Figure 1

Existing technologies to track GPCRs in living cells, represented at the same scale. Representation of a GPCR based on the structure of sensory rhodopsin II (A; Protein Data Bank identifier (PDB ID), 1GUE), the structure of the peptide ligand porcine neuropeptide Y (B; PDB ID, 1F8P), the structure of an auto-fluorescent protein, namely the S65A/Y66F GFP variant (C; PDB ID, 2HGD), the structure of an immunoglobulin gamma (D; PDB ID 1IGT), the Lumio™-tag (E), the SNAP™-tag based on the structure of the human O⁶-alkylguanine-DNA alkyltransferase, (F; PDB ID, 1EH6).