Heterotrimeric G proteins have a crucial role as molecular switches in signal transduction pathways mediated by G-protein-coupled receptors (GPRs).
Extracellular stimuli activate these receptors, which then catalyse GTP-GDP exchange on the G protein alpha-subunit.
The complex series of interactions and conformational changes that connect agonist binding to G protein activation raise various interesting questions about the structure, biomechanics, kinetics and specificity of signal transduction across the plasma membrane.
See also
GPRs (G-protein-coupled receptors)
References
Oldham WM, Hamm HE. Heterotrimeric G protein activation by G-protein-coupled receptors. Nat Rev Mol Cell Biol. 2008 Jan;9(1):60-71. PMID: 18043707
Weinstein LS, Chen M, Xie T, Liu J. Genetic diseases associated with heterotrimeric G proteins. Trends Pharmacol Sci. 2006 May;27(5):260-6. PMID: 16600389