Gi alpha subunit
|guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 1|
|Locus||Chr. 7 q21-q22|
|guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 2|
|Locus||Chr. 3 p21|
|guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 3|
|Locus||Chr. 1 p13|
Gi alpha subunit (Gαi, or Gi/G0 or Gi protein) is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP. A mnemonic for remembering this subunit is to look at first letter (Gαi = Adenylate Cyclase inhibitor).
The following G protein-coupled receptors couple to the Gi subunit:
- Acetylcholine M2 & M4 receptors
- Adenosine A1 & A3 receptors
- Adrenergic α2A, α2B, & α2C receptors
- Apelin receptors
- Calcium-sensing receptor
- Cannabinoid receptors (CB1 and CB2)
- Chemokine CXCR4 receptor
- Dopamine D2, D3, D4
- GABAB receptor
- Glutamate mGluR2, mGluR3, mGluR4, mGluR6, mGluR7, & mGluR8 receptors
- Histamine H3 & H4 receptors
- Melatonin MT1, MT2, & MT3 receptors
- Niacin receptors NIACR1 & NIACR2
- Opioid δ, κ, μ, & nociceptin receptors
- Prostaglandin EP1, EP3, FP, & TP receptors
- Serotonin 5-HT1 & 5-HT5 receptors
- Somatostatin sst1, sst2, sst3, sst4 & sst5 receptors
- Trace amine-associated receptor 8
Gi mainly inhibits the cAMP dependent pathway by inhibiting adenylate cyclase activity, decreasing the production of cAMP from ATP, which, in turn, results in decreased activity of cAMP-dependent protein kinase. Therefore, the ultimate effect of Gi is the opposite of cAMP-dependent protein kinase.
It is also attributed a minor role in activation of the phospholipase C pathway. Growth hormone is required for normal postnatal growth, bone growth, regulatory effects on protein, carbohydrate, and lipid metabolism. although this is mainly a function of the Gq alpha subunit.
There are several types of Gi: Gia1, Gia2, Gia3 and Gia4
Gia1 or Gi1 is encoded by the gene GNAI1.
Gia2 or Gi2 is encoded by the gene GNAI2.
Gia3 or Gi3 is encoded by the gene GNAI3.
- Birnbaumer L (April 2007). "Expansion of signal transduction by G proteins. The second 15 years or so: from 3 to 16 alpha subunits plus betagamma dimers". Biochim. Biophys. Acta 1768 (4): 772–93. doi:10.1016/j.bbamem.2006.12.002. PMC 1993906. PMID 17258171.
- Obál F, Krueger J (2001). "The somatotropic axis and sleep.". Rev Neurol (Paris) 157 (11 Pt 2): S12–5. PMID 11924022.
- GeneGlobe -> GHRH Signaling Retrieved on May 31, 2009