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File:G protein1.png

This heterotrimeric G protein is illustrated with its theoretical lipid anchors. GDP is black. Alpha chain is yellow. Beta and gamma chains are blue.

File:G-Protein.png

3D structure of a heterotrimeric G protein

File:G protein (heterotrimeric).png

An heterotrimeric G protein. GDP is in purple. Alpha chain in orange. Beta chain in blue. Gamma chain in green. An important loop for signal transduction is shown in red (PDB code=1gg2) (more details...)

"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[edit | edit source]

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 four main families:

Beta-gamma complex[edit | edit source]

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[edit | edit source]

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[edit | edit source]

References[edit | edit source]

  1. 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.

External links[edit | edit source]

Template:GTPases

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