Domain Annotation: SCOP2 Classification SCOP2 Database Homepage

ChainsTypeFamily Name Domain Identifier Family IdentifierProvenance Source (Version)
ASCOP2B SuperfamilyRas-like P-loop GTPases 8019719 3002022 SCOP2B (2022-06-29)
ASCOP2B SuperfamilyGalpha insert domain-like 8056777 3000669 SCOP2B (2022-06-29)
ASCOP2B SuperfamilyRas-like P-loop GTPases 8019719 3002022 SCOP2B (2022-06-29)

Domain Annotation: ECOD Classification ECOD Database Homepage

ChainsFamily NameDomain Identifier ArchitecturePossible HomologyHomologyTopologyFamilyProvenance Source (Version)
AG-alphae1bh2A1 A: alpha arraysX: Transducin (alpha subunit), insertion domain (From Topology)H: Transducin (alpha subunit), insertion domain (From Topology)T: Transducin (alpha subunit), insertion domainF: G-alphaECOD (1.6)
ARase1bh2A2 A: a/b three-layered sandwichesX: P-loop domains-likeH: P-loop domains-relatedT: P-loop containing nucleoside triphosphate hydrolasesF: RasECOD (1.6)

Domain Annotation: CATH CATH Database Homepage

ChainDomainClassArchitectureTopologyHomologyProvenance Source (Version)
A3.40.50.300 Alpha Beta 3-Layer(aba) Sandwich Rossmann fold P-loop containing nucleotide triphosphate hydrolasesCATH (4.3.0)
A1.10.400.10 Mainly Alpha Orthogonal Bundle GI Alpha 1, domain 2-like GI Alpha 1, domain 2-likeCATH (4.3.0)

Protein Family Annotation Pfam Database Homepage

ChainsAccessionNameDescriptionCommentsSource
PF00503G-protein alpha subunit (G-alpha)G-protein alpha subunitG proteins couple receptors of extracellular signals to intracellular signaling pathways. The G protein alpha subunit binds guanyl nucleotide and is a weak GTPase. A set of residues that are unique to G-alpha as compared to its ancestor the Arf-like ...G proteins couple receptors of extracellular signals to intracellular signaling pathways. The G protein alpha subunit binds guanyl nucleotide and is a weak GTPase. A set of residues that are unique to G-alpha as compared to its ancestor the Arf-like family form a ring of residues centered on the nucleotide binding site [3]. A Ggamma is found fused to an inactive Galpha in the Dictyostelium protein gbqA [3].
Domain

Gene Ontology: Gene Product Annotation Gene Ontology Database Homepage

ChainsPolymerMolecular FunctionBiological ProcessCellular Component
GUANINE NUCLEOTIDE-BINDING PROTEIN

Structure Motif Annotation: Mechanism and Catalytic Site Atlas M-CSA Database Homepage

ChainsEnzyme NameDescriptionCatalytic Residues
G-protein alpha subunit, group I (GTPase)  M-CSA #533

The alpha subunits of heterotrimeric G proteins are members of the Ras superfamily of GTP hydrolases and function in signal transduction. They are activated by replacement of bound GDP by GTP, a process promoted by activated 7-transmembrane receptors, and by subsequent dissociation of the alpha subunit from the beta and gamma subunits. The G-alpha subunit remains active until its GTPase activity converts the bound GTP back to GDP.

The alpha subunit of the G protein Gi1 is expressed in many different tissues and is activated by the alpha-2 adrenergic and M-2 muscarinic cholinergic receptors, amongst others. Its downstream effectors include particular isoforms of adenylate cyclase; types V and VI are particularly sensitive to inhibition by G-alpha-i1.

The mechanism of enzymatic GTP hydrolysis (and similar phosphoryl transfer reactions) has been subject to significant debate and still remains to be firmly established. More recent models have proposed a dissociative-like process, in which the transition state shows significant cleavage of the gamma-beta phosphoanhydride bond and relatively little bond formation between the gamma phosphate and the nucleophilic water molecule. (See, for example, the reference pubmed ID 15236956 for a recent discussion).

Defined by 5 residues: GLU:A-12 [auth A-43]THR:A-17 [auth A-48]ARG:A-147 [auth A-178]ASP:A-169 [auth A-200]GLN:A-173 [auth A-204]
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