Heterotrimeric G protein
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"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]
Alpha subunits
Gα subunits consist of two domains, the GTPase domain, and the alpha-helical domain. There exist at least 20 different Gα subunits, which are separated into several main families:
- Gαs or simply Gs (stimulatory) - activates adenylate cyclase to increase cAMP synthesis
- Gαi or simply Gi (inhibitory) - inhibits adenylate cyclase
- Golf (olfactory) - couples to olfactory receptors
- Gt (transducin) - transduces visual signals in conjunction with rhodopsin in the retina
- Gq - stimulates phospholipase C
- The G12/13 family - important for regulating (via guanine nucleotide exchange factors) the cytoskeleton, cell junctions, and other processes related to movements
Beta-gamma complex
The β and γ subunits are closely bound to one another and are referred to as the beta-gamma complex. The Gβγ complex is released from the Gα subunit after its GDP-GTP exchange.
Function
The free Gβγ complex can act as a signaling molecule itself, by activating other second messengers or by gating ion channels directly.
For example, the Gβγ complex, when bound to histamine receptors, can activate phospholipase A2. Gβγ 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
References
External links
Acid anhydride hydrolases: GTPases/G proteins (EC 3.6.5) | |
|---|---|
| 3.6.5.1: Heterotrimeric G protein | Gαs - Gαi (GNAI1, GNAI2, GNAI3) - Gαq/11 (GNAQ, GNA11) - Gα12/13 (GNA12, GNA13) - Transducin (GNAT1, GNAT2) |
| 3.6.5.2: Small GTPase > Ras superfamily | Ras - Rab (Rab27) - Arf (Arf6) - Ran - Rheb - Rho family (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 |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
