Gi alpha subunit

G_i alpha subunit (G_αi, or G_i/G₀ or G_i protein) is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.^[1] A mnemonic for remembering this subunit is to look at first letter (G_αi = Adenylyl Cyclase inhibitor).

Receptors

The following G protein-coupled receptors couple to the G_i subunit:

Acetylcholine M₂ & M₄ receptors
Adenosine A₁ & A₃ receptors
Adrenergic α_2A, α_2B, & α_2C receptors
Apelin receptors
Calcium-sensing receptor
Cannabinoid receptors (CB1 and CB2)
Chemokine CXCR4 receptor
Dopamine D₂, D₃, D₄
GABA_B receptor
Glutamate mGlu₂, mGlu₃, mGlu₄, mGlu₆, mGlu₇, & mGlu₈ receptors
Histamine H₃ & H₄ receptors
Melatonin MT₁, MT₂, & MT₃ receptors
Hydroxycarboxylic acid receptors: HCA1, HCA2, & HCA3
Opioid δ, κ, μ, & nociceptin receptors
Prostaglandin EP₁, EP₃, FP, & TP receptors
Serotonin 5-HT₁ & 5-HT₅ receptors
Short chain fatty acid receptors: FFAR2 & FFAR3
Somatostatin sst1, sst2, sst3, sst4 & sst5 receptors
Trace amine-associated receptor 8

Function

G_i 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 G_i is the opposite of cAMP-dependent protein kinase.

It is also attributed a minor role in activation of the phospholipase C pathway.^[2] Growth hormone is required for normal postnatal growth, bone growth, regulatory effects on protein, carbohydrate, and lipid metabolism.^[3] Although this is mainly a function of the G_q alpha subunit.

Types

There are several types of G_i: Gia1, Gia2, Gia3 and Gia4

Gia1

Gia1 or G_i1 is encoded by the gene GNAI1.

Gia2

Gia2 or G_i2 is encoded by the gene GNAI2.

Gia3

Gia3 or G_i3 is encoded by the gene GNAI3.

References

↑ 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

External links

Gi+alpha+Subunit at the US National Library of Medicine Medical Subject Headings (MeSH)

[pmid17258171-1] 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.

[2] Obál F, Krueger J (2001). “The somatotropic axis and sleep”. Rev Neurol (Paris). 157 (11 Pt 2): S12–5. PMID 11924022.

[GeneGlobe-3] GeneGlobe -> GHRH Signaling Retrieved on May 31, 2009

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