G_i alpha subunit

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 2
guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 2
Identifiers
Symbol	GNAI2
Alt. symbols	GNAI2B
NCBI gene	2771
HGNC	4385
OMIM	139360
RefSeq	NM_002070
UniProt	P04899
Other data
Locus	Chr. 3 p21
Structures
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Structures	Swiss-model
Domains	InterPro

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Structures	Swiss-model
Domains	InterPro

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 1
guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 1
Identifiers
Symbol	GNAI1
NCBI gene	2770
HGNC	4384
OMIM	139310
RefSeq	NM_002069
UniProt	P63096
Other data
Locus	Chr. 7 q21-q22
Structures
Search for
Structures	Swiss-model
Domains	InterPro

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 3

Identifiers

Symbol

Other data

Chr. 1 p13

Search for
Structures	Swiss-model
Domains	InterPro

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 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
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 U.S. 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

[1]

[2]

[3]

v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)