| A 16aa peptide within the extracellular, N-terminal domain or human, and a 20-aa peptide mapping at the cytoplasmic, C-terminal domain of rat NMUR2. The neuromedins (Nm) are a family of bioactive peptides best known for their roles in smooth muscle contraction. Nm family of bioactive peptides include: Bombesin-like (NmB, NmC), kassinin-like (NmL and NmK or neurokinins A and B), neurotensin-like (NmN), and neuromedin U (NmU, for its ability to stimulate uterine muscle contraction). Besides its roles in smooth muscle contraction (human ileum, urinary bladder, rat stomach etc), NmU has also been implicated in hypertension, blood flow in intestine, and neurotransmission. Recently two structurally related, orphan G-protein coupled receptors, termed NMUR1 (GPCR66/FM-3/SNORF62) and NMUR2 (TGR-1/FM-4/SNORF72), have been identified as cognate receptors of NmU. NMU receptors display a typical 7 TM domains with extracellular N-terminus and intracellular C-terminus. NMUR1 is found at low levels in uterus, where NmU has robust contractile activity and strong specific NmU binding sites have been found in uterus suggesting the presence of another NmU receptor. A novel GPCR, termed NMUR2 (FM-4/TGR-1/SNORF72) has been identified as the 2nd receptor for NmU. NMUR2 (rat 395 aa, human 415 aa, chromosome 5q31.1, ~78% homology) has approx 50% homology with NMUR1. NMUR2 also couples to Gq in the signal transduction pathway. Unlike NMUR1, NMUR2 was primarily expressed in the rat uterus, and brain. Moderate to low level of expression was found in rat lung, ovary, and GI-tract. In human, NMUR2 has highest expression in testing and brain. Moderate expression was also detected in kidney, lung, and thyroid. |
