Editing G protein (section)

==== Activation ====
When a [[ligand (biochemistry)|ligand]] activates the [[G protein-coupled receptor]], it induces a conformational change in the receptor that allows the receptor to function as a [[guanine nucleotide exchange factor]] (GEF) that exchanges GDP for GTP. The GTP (or GDP) is bound to the G<sub>α</sub> subunit in the traditional view of heterotrimeric GPCR activation. This exchange triggers the dissociation of the G<sub>α</sub> subunit (which is bound to GTP) from the G<sub>βγ</sub> dimer and the receptor as a whole. However, models which suggest molecular rearrangement, reorganization, and pre-complexing of effector molecules are beginning to be accepted.<ref name="Kou Qin">{{cite journal | vauthors = Qin K, Dong C, Wu G, Lambert NA | title = Inactive-state preassembly of G(q)-coupled receptors and G(q) heterotrimers | journal = Nature Chemical Biology | volume = 7 | issue = 10 | pages = 740–7 | date = August 2011 | pmid = 21873996 | pmc = 3177959 | doi = 10.1038/nchembio.642 }}</ref><ref name="pmid17095603">{{cite journal | vauthors = Digby GJ, Lober RM, Sethi PR, Lambert NA | title = Some G protein heterotrimers physically dissociate in living cells | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 47 | pages = 17789–94 | date = November 2006 | pmid = 17095603 | pmc = 1693825 | doi = 10.1073/pnas.0607116103 | bibcode = 2006PNAS..10317789D | doi-access = free }}</ref><ref name="pmid19089952">{{cite journal | vauthors = Khafizov K, Lattanzi G, Carloni P | title = G protein inactive and active forms investigated by simulation methods | journal = Proteins | volume = 75 | issue = 4 | pages = 919–30 | date = June 2009 | pmid = 19089952 | doi = 10.1002/prot.22303 | s2cid = 23909821 }}</ref> Both G<sub>α</sub>-GTP and G<sub>βγ</sub> can then activate different ''signaling cascades'' (or ''[[second messenger]] pathways'') and effector proteins, while the receptor is able to activate the next G protein.<ref name="pmid20348012">{{cite journal | vauthors = Yuen JW, Poon LS, Chan AS, Yu FW, Lo RK, Wong YH | title = Activation of STAT3 by specific Galpha subunits and multiple Gbetagamma dimers | journal = The International Journal of Biochemistry & Cell Biology | volume = 42 | issue = 6 | pages = 1052–9 | date = June 2010 | pmid = 20348012 | doi = 10.1016/j.biocel.2010.03.017 }}</ref>