Two distinct conformers of SAG investigated by solution NMR and variable-temperature experiments.

SAG (Smo agonist) is high specific agonist of Smo receptor, it is widely used as chemical probe to explore the therapeutic value of activating the Hh-signaling pathway. In the present work, the coexistence of two distinct conformers (A and B) of SAG are revealed by solution NMR, the 3D structural difference of the two conformers are elucidated by ROESY spectroscopy and MMFF94 program. It is discovered that both conformers are agonists of Smo receptor, and the minor conformer (conformer B) in D2 O solution has higher affinity to Smo receptor by molecular docking. The result showed the detail about two distinct conformers of SAG are involved in activation of Smo receptor, and also provides information for designing more effective agonist of Smo by mimicking B conformer of SAG. By exchange dynamics investigation using variable-temperature NMR experiments, the ratio of two conformers has been shown to be drastically solvent dependent, so, the menstruum type is another important influence factor of SAG bioactivity, when using SAG as chemical probe.