have different isoforms, and some combination of isoforms result in dimerization while other combinations do not. For example, beta1 binds both gamma subunits while beta3 binds neither. Upon activation of the GPCR, 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). When acetylcholine is the extracellular ligand in the pathway, the heart cell hyperpolarizes normally to decrease heart muscle contraction. When substances such as muscarine act as ligands, the dangerous amount of hyperpolarization leads to hallucination. Therefore, proper functioning of Gβγ plays a key role in our physiological well-being. The last function is activating L-type calcium channels, as in H3 receptor pharmacology. Heterotrimeric G-proteins in Plants Heterotrimeric G-protein signaling in plants deviates from the metazoan model at various levels. For example, the presence of extra-Large G alpha, loss of G alpha and Regulator of G-protein signaling (RGS) in many plant lineages. In addition, the G-proteins are not essential for the survival in dicotyledonous plants, while they are essential for the survival of monocotyledonous plants. References External links Peripheral membrane proteins EC 3.6.5