Chemical structures of parmodulins and comparison with those of other intracellularly bound GPCR ligands. (A) Chemical structures of JF5 (parmodulin 1), ML159 (parmodulin 3), ML160 (parmodulin 4), ML161 (parmodulin 2), and NRD-21. Other intracellular GPCR ligands are shown below the parmodulins. (B) Largest common substructure TC between parmodulins and other intracellular GPCR ligands. The receptor or receptor family targeted by the substances is indicated on the left-hand side of the matrix.