Gi alpha subunit

Gi alpha subunit (or Gi/G0 or Gi protein) is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.

Receptors
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
 * 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
 * Opioid δ, κ, μ, & nociceptin receptors
 * Prostaglandin EP1, EP3, FP, & TP receptors
 * Serotonin 5-HT1 & 5-HT5 receptors

Function
See also: function of cAMP-dependent protein kinase

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.

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

Gia1
Gia1 or Gi1 is encoded by the gene GNAI1.

Gia2
Gia2 or Gi2 is encoded by the gene GNAI2.

Gia3
Gia3 or Gi3 is encoded by the gene GNAI3.