Homologous Superfamily

G protein alpha subunit, helical insertion (IPR011025)

Short name: GproteinA_insert

Overlapping entries


Guanine nucleotide binding proteins (G proteins) are membrane-associated, heterotrimeric proteins composed of three subunits: alpha (IPR001019), beta (IPR001632) and gamma (IPR001770) [PMID: 15119945]. 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 [PMID: 12517447]. This superfamily represents the G protein alpha subunit helical insertion domain.

GO terms

Biological Process

GO:0007165 signal transduction

Molecular Function

No terms assigned in this category.

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.