Gi alpha subunit

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 1
Identifiers
Symbol	GNAI1
Entrez	2770
HUGO	4384
OMIM	139310
RefSeq	NM_002069
UniProt	P63096
Other data
Locus	Chr. 7 q21-q22

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 2
Identifiers
Symbol	GNAI2
Alt. symbols	GNAI2B
Entrez	2771
HUGO	4385
OMIM	139360
RefSeq	NM_002070
UniProt	P04899
Other data
Locus	Chr. 3 p21

guanine nucleotide-binding protein (G protein), alpha inhibiting activity polypeptide 3
Identifiers
Symbol	GNAI3
Entrez	2773
HUGO	4387
OMIM	139370
RefSeq	NM_006496
UniProt	P08754
Other data
Locus	Chr. 1 p13

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 = Adenylate 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 US National Library of Medicine Medical Subject Headings (MeSH)

Intracellular signaling peptides and proteins

MAP

see MAP kinase pathway

Calcium

G protein

Heterotrimeric

cAMP:	Heterotrimeric G protein Gs/Gi Adenylate cyclase cAMP 3',5'-cyclic-AMP phosphodiesterase Protein kinase A

cGMP:	Transducin Guanylate cyclase cGMP 3',5'-cyclic-GMP phosphodiesterase Protein kinase G

G alpha subunit G_α GNAO1 GNAI1 GNAI2 GNAI3 GNAT1 GNAT2 GNAT3 GNAZ GNAS GNAL GNAQ GNA11 GNA12 GNA13 GNA14 GNA15/GNA16

G beta-gamma complex G_β GNB1 GNB2 GNB3 GNB4 GNB5 G_γ GNGT1 GNGT2 GNG2 GNG3 GNG4 GNG5 GNG7 GNG8 GNG10 GNG11 GNG12 GNG13 BSCL2

G protein-coupled receptor kinase AMP-activated protein kinase

Monomeric

Cyclin

Lipid

Other protein kinase

Serine/threonine:	Casein kinase 1 2 eIF-2 kinase EIF2AK3 Glycogen synthase kinase GSK1 GSK2 GSK-3 GSK3A GSK3B IκB kinase CHUK IKK2 IKBKG Interleukin-1 receptor-associated kinase IRAK1 IRAK2 IRAK3 IRAK4 Lim kinase LIMK1 LIMK2 p21-activated kinases PAK1 PAK2 PAK3 PAK4 Rho-associated protein kinase ROCK1 ROCK2 Ribosomal s6 kinase RPS6KA1

Tyrosine:	ZAP70 Focal adhesion protein-tyrosine kinase PTK2 PTK2B BTK

both	Dual-specificity kinase

Other protein phosphatase

Serine/threonine:	Protein phosphatase 2

Tyrosine:	protein tyrosine phosphatase: Receptor-like protein tyrosine phosphatase Sh2 domain-containing protein tyrosine phosphatase

both:	Dual-specificity phosphatase

Apoptosis

see apoptosis signaling pathway

GTP-binding protein regulators

see GTP-binding protein regulators

Other

see also deficiencies of intracellular signaling peptides and proteins

Hydrolases: acid anhydride hydrolases (EC 3.6)

3.6.1

3.6.2

3.6.3-4: ATPase

3.6.3

Cu++ (3.6.3.4)	Menkes/ATP7A Wilson/ATP7B

Ca+ (3.6.3.8)	SERCA ATP2A1 ATP2A2 ATP2A3 Plasma membrane ATP2B1 ATP2B2 ATP2B3 ATP2B4 SPCA ATP2C1 ATP2C2

Na+/K+ (3.6.3.9)	ATP1A1 ATP1A2 ATP1A3 ATP1A4 ATP1B1 ATP1B2 ATP1B3 ATP1B4

H+/K+ (3.6.3.10)	ATP4A

Other P-type ATPase	ATP8B1 ATP10A ATP11B ATP12A ATP13A2 ATP13A3

3.6.4

3.6.5: GTPase

3.6.5.1: Heterotrimeric G protein	G_αs G_αi GNAI1 GNAI2 GNAI3 G_αq/11 GNAQ GNA11 G_α12/13 GNA12 GNA13 Transducin GNAT1 GNAT2

3.6.5.2: Small GTPase > Ras superfamily	Rho family of GTPases: Cdc42 CDC42 TC10 TCL RhoUV RhoU RhoV Rac Rac1 2 3 RhoG RhoBTB 1 2 RhoH Rho A B C Rnd 1 2 3 RhoDF RhoF RhoD other: Ras HRAS KRAS NRAS Rab RAB23 RAB27 Arf ARF6 SAR1B ARL13B ARL6 Ran Rheb Rap RGK

3.6.5.3: Protein-synthesizing GTPase	Prokaryotic IF-2 EF-Tu EF-G Eukaryotic

3.6.5.5-6: Polymerization motors	Dynamin Tubulin

Proteins: enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases(list) EC2 Transferases(list) EC3 Hydrolases(list) EC4 Lyases(list) EC5 Isomerases(list) EC6 Ligases(list)

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