Orphan G protein‐coupled receptors; Orphan GPCRs; Orphan serpentine receptors; Orphan nuclear receptor
Orphan receptors are proteins that bind and are activated by hitherto unknown signaling molecules (called ligands, neurotransmitters, or hormones). However, they share structural components with identified receptors whose signaling molecules are already known. The physiological functions of orphan receptors are unidentified. The identification of the natural ligand of an orphan receptor holds the key to our understanding of its physiological role and potential as a drug target.
Members of two structurally very distinct receptor families are termed orphan receptors. One is the family of the nuclear receptors which are cytosolic proteins that upon ligand binding change their conformation, translocate to nuclear binding sites, and act as transcription factors to regulate the expression of other genes. The second group of receptor proteins is the G...
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