Gi alpha subunit

G protein subunit alpha i1
Identifiers
Symbol	GNAI1
Entrez	2770
HUGO	4384
OMIM	139310
PDB	3UMR
RefSeq	NM_002069
UniProt	P63096
Other data
Locus	Chr. 7 q21-q22

G protein subunit alpha i2
Identifiers
Symbol	GNAI2
Entrez	2771
HUGO	4385
OMIM	139360
RefSeq	NM_002070
UniProt	P04899
Other data
Locus	Chr. 3 p21

G protein subunit alpha i3
Identifiers
Symbol	GNAI3
Entrez	2773
HUGO	4387
OMIM	139370
PDB	2ODE
RefSeq	NM_006496
UniProt	P08754
Other data
Locus	Chr. 1 p13

G protein subunit alpha o1
Identifiers
Symbol	GNAO1
Entrez	2775
HUGO	4389
OMIM	139311
RefSeq	NM_020988
UniProt	P09471
Other data
Locus	Chr. 16 q13

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. 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

See also: function of cAMP-dependent protein kinase

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. 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 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.

See also

• Second messenger system

External links

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