Heterotrimeric G protein

"G protein" usually refers to the membrane-associated heterotrimeric G proteins, sometimes referred to as the "large" G proteins. These proteins are activated by G protein-coupled receptors and are made up of alpha (α), beta (β) and gamma (γ) subunits.^[1]

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1 Alpha subunits
2 Beta-gamma complex
- 2.1 Function
- 2.2 Genes
3 References

Alpha subunits

G_α subunits consist of two domains, the GTPase domain, and the alpha-helical domain. There exist at least 20 different G_α subunits, which are separated into several main families:

G_αs or simply G_s (stimulatory) - activates adenylate cyclase to increase cAMP synthesis
- GNAS
G_αi or simply G_i (inhibitory) - inhibits adenylate cyclase
- GNAI1, GNAI2, GNAI3, GNAZ, GNAO1
G_olf (olfactory) - couples to olfactory receptors
- GNAL
G_t (transducin) - transduces visual signals in conjunction with rhodopsin in the retina
- GNAT1, GNAT2, GNAT3
G_q - stimulates phospholipase C
- GNAQ, GNA11, GNA14, GNA15
The G_12/13 family - important for regulating (via guanine nucleotide exchange factors) the cytoskeleton, cell junctions, and other processes related to movements
- GNA12, GNA13

Beta-gamma complex

The β and γ subunits are closely bound to one another and are referred to as the beta-gamma complex. The G_βγ complex is released from the G_α subunit after its GDP-GTP exchange.

Function

The free G_βγ complex can act as a signaling molecule itself, by activating other second messengers or by gating ion channels directly.

For example, the G_βγ complex, when bound to histamine receptors, can activate phospholipase A₂. G_βγ complexes bound to muscarinic acetylcholine receptors, on the other hand, directly open G-protein coupled inward rectifying potassium channels (GIRKs). They can also activate L-type calcium channels, as in H₃ receptor pharmacology.

Genes

G_β genes: GNB1, GNB2, GNB3, GNB4, GNB5, GNB1L, GNB2L1

G_γ genes: GNGT1, GNGT2, GNG2, GNG3, GNG4, GNG5, GNG7, GNG8, GNG10, GNG11, GNG12, GNG13

References

^ Hurowitz EH, Melnyk JM, Chen YJ, Kouros-Mehr H, Simon MI, Shizuya H (2000). "Genomic characterization of the human heterotrimeric G protein alpha, beta, and gamma subunit genes". DNA Res 7 (2): 111-20. doi:10.1093/dnares/7.2.111. PMID 10819326.

v • d • e Acid anhydride hydrolases: GTPases/G proteins (EC 3.6.5)
3.6.5.1: Heterotrimeric G protein	G_αs - G_αi - G_αq/11 - G_α12/13 - Transducin
3.6.5.2: Small GTPase	Ras - Rab (Rab27) - Arf (Arf6) - Ran - Rheb - Rho (RhoA, RhoB, CDC42, Rac1) - Rap
3.6.5.3: Elongation factor	Prokaryotic - Eukaryotic
3.6.5.5-6: Other	Dynamin (is a GTPase, is not a G protein) - Tubulin

Categories: G proteins | Membrane biology | Peripheral membrane proteins

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Heterotrimeric_G_protein". A list of authors is available in Wikipedia.