GTP-binding protein

Function

GTP-binding proteins or G proteins are transmitting signals outside the cell which cause changes within the cell. They act as molecular switches which are on when binding GTP and off when binding GDP. GTP-binding proteins belong to two families: heterotrimeric G proteins^[1] and small GTPases^[2]. The structure of small GTPase is homologous to that of the α subunit of heterotrimeric G protein. See details on small GTP-binding protein LepA in LepA.

Heterotrimeric G protein or guanine nucleotide-binding protein or G protein (GNBP) are heterodimeric membrane proteins composed of α, β and γ subunits. GNBP is involved in mammalian cellular signaling pathways. GNBP α subunit binds GDP or GTP. When bound to GTP it dissociates from the β and γ subunits, binds to adenylate cyclase which converts ATP to cAMP. See also

G protein-coupled receptor
Beta2 adrenergic receptor-Gs protein complex.

Disease

Mutations in heterotrimeric G protein α subunit were identified in endocrine tumors and in McCune-Albright syndrome^[3].

Structural highlights

E. coli small GTPase ERA binds GDP in a cavity formed by ^[4]. . Water molecules shown as red spheres.