Beta-gamma complex

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

A 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...)

The beta-gamma complex is composed of the heterotrimeric G proteins G_β (beta subunit) and G_γ (gamma subunit) that are closely bound to one another.

Upon activation of a G-protein coupled receptor, the G_βγ complex is released from the G_α subunit, allowing the G_α subunit to function as a messenger in signal transduction.

Function

The normal role of the beta-gamma complex is inhibition of the G_α subunit. However, the free G_βγ complex can act as a signaling molecule itself, by activating other second messengers or by gating ion channels directly.

Examples of G_βγ complex functions include:

• Activation of phospholipase A₂ when bound to histamine receptors
• Direct opening of G-protein coupled inward rectifying potassium channels (GIRKs) when bound to muscarinic acetylcholine receptors
• Activation L-type calcium channels, as in H₃ receptor pharmacology.
• Initiation of the phospholipase C pathway by activating phospholipase C, as a minor mechanism of growth hormone releasing hormone releasing growth hormone.^[1]

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