Smoothened is a protein that is not a G protein-coupled receptor (it is instead a GPCR-like receptor) that is a component of the hedgehog signaling pathway and is conserved from flies to humans. It is the molecular target of the teratogen cyclopamine. Cellular localization plays an essential role in the function of SMO. Stimulation of the patched receptor by the sonic hedgehog ligand leads to translocation of SMO to the primary cilium. Furthermore, SMO that is mutated in the domain required for ciliary localisation cannot contribute to pathway activation. SMO has also been shown to bind the kinesin motor protein Costal-2 and play a role in the localization of the Ci (Cubitus interruptus transcription factor) complex.