Neuromedin B

 ( Neuropeptides ) 

Neuromedin B (NMB) is a bombesin-related peptide in mammals. It was originally purified from pig spinal cord, and later shown to be present in human central nervous system and gastrointestinal tract.

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Sequence The sequence of the C-terminal decapeptide is highly conserved across mammalian species: GNLWATGHFM-(NH2); this decapeptide is sometimes noted as neuromedin B, but it is more accurately described as neuromedin B 23-32. The sequence of neuromedin B (in rat) is: TPFSWDLPEPRSRASKIRVHPRGNLWATGHFM-(NH2). The (NH2) here indicates a post-translational modification -- alpha amidation of the carboxy terminus.

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Function Neuromedin regulates the following functions:

• exocrine gland and endocrine system secretions
• cell growth
• body temperature
• blood pressure and glucose level
• sneezing

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Neuromedin signaling pathway NMB acts by binding to its high affinity cell surface receptor, neuromedin B receptor (NMBR). This receptor is a G protein-coupled receptor with seven transmembrane spanning regions, hence the receptor is also denoted as a 7-transmembrane receptor (7-TMR). Upon binding several intracellular signaling pathways are triggered (see Figure 2).

When NMB binds to its 7-TMR, the heterotrimeric G protein that is attached to the receptor is activated. The G-protein is called heterotrimeric because it consists of 3 polypeptides: α subunit, β subunit, and γ subunit. In the activated NMBR/G-protein complex, there occurs an exchange of GTP for GDP bound to G-α subunit. The G-α subunit, in turn, dissociated form the G-βγ subunits. The free G-α inactivates adenylate cyclase (AC), which, in turn, catalyzes the conversion of ATP to cAMP, the latter of which functioning as a second messenger. cAMP activates of the enzyme Protein Kinase A (PKA). PKA enters the nucleus and activates the CREB protein. The activated CREB binds along with CREB binding protein, co-activator to the CRE region of the DNA in the nucleus. CREB and CBP are held together by . CRE is the control that activates number of growth factors, and thus cell proliferation and some anti-apoptotic genes. In the brain, CREB plays a role in long-term memory and learning.

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