Member database | CATH-Gene3D |
CATH-Gene3D type | homologous superfamily |
Description Imported from IPR011025
Guanine nucleotide binding proteins (G proteins) are membrane-associated, heterotrimeric proteins composed of three subunits: alpha (
IPR001019), beta (
IPR001632) and gamma (
IPR001770)
[1]. G proteins act as signal transducers, relaying a signal from a ligand-activated GPCR (G protein-coupled receptor) to an enzyme or ion channel effector. The activated GPCR promotes the exchange of GDP for GTP on the G protein alpha subunit, allowing the trimeric G protein to be released from the receptor and to dissociate into active (GTP-bound) alpha subunit and beta/gamma dimer, both of which activate distinct downstream effectors. There are several isoforms of each subunit, which together can makeup hundreds of combinations of G proteins, each one linking a specific receptor to a certain effector.
The heterotrimeric G protein alpha subunit is composed of two domains: a GTP-binding domain and a helical insertion domain. The GTP-binding domain is homologous to Ras-like small GTPases, and includes switch regions I and II, which change conformation during activation. The helical insertion domain is inserted into the GTP-binding domain before switch region I, and is unique to heterotrimeric G proteins. This helical insertion domain functions to sequester the guanine nucleotide at the interface with the GTP-binding domain and must be displaced to enable nucleotide dissociation
[2]. This superfamily represents the G protein alpha subunit helical insertion domain.
References Imported from IPR011025
1.Biochemistry of transmembrane signaling mediated by trimeric G proteins. Svoboda P, Teisinger J, Novotny J, Bourova L, Drmota T, Hejnova L, Moravcova Z, Lisy V, Rudajev V, Stohr J, Vokurkova A, Svandova I, Durchankova D. Physiol Res 53 Suppl 1, S141-52, (2004). PMID: 15119945
2.Activation of G-protein Galpha subunits by receptors through Galpha-Gbeta and Galpha-Ggamma interactions. Cherfils J, Chabre M. Trends Biochem. Sci. 28, 13-7, (2003). View articlePMID: 12517447