Melanin-concentrating hormone receptor: an orphan receptor fits the key.

The melanin-concentrating hormone (MCH), a hypothalamic peptide, was identified initially in teleost fish as a regulator of pigmentary changes in background adaptation, and was later also found, in mammals, to be a regulator of feeding and energy homeostasis. Its specific receptor remained an enigma until very recently when it was identified as the orphan G-protein-coupled receptor SLC-1. This review focuses on the identification, structure and signaling of the MCH receptor and discusses some of the implications of its discovery.