Résumé
DISPLAYTITLE:Gi alpha subunit Gi protein alpha subunit is a family of heterotrimeric G protein alpha subunits. This family is also commonly called the Gi/o (Gi /Go ) family or Gi/o/z/t family to include closely related family members. G alpha subunits may be referred to as Gi alpha, Gαi, or Giα. There are four distinct subtypes of alpha subunits in the Gi/o/z/t alpha subunit family that define four families of heterotrimeric G proteins: Gi proteins: Gi1α, Gi2α, and Gi3α Go protein: Goα (in mouse there is alternative splicing to generate Go1α and Go2α) Gz protein: Gzα Transducins (Gt proteins): Gt1α, Gt2α, Gt3α Gi1α is encoded by the gene GNAI1. Gi2α is encoded by the gene GNAI2. Gi3α is encoded by the gene GNAI3. Go1α is encoded by the gene GNAO1. Gzα is encoded by the gene GNAZ. Transducin Transducin/Gt1α is encoded by the gene GNAT1. Transducin 2/Gt2α is encoded by the gene GNAT2. Gustducin Gustducin/Gt3α is encoded by the gene GNAT3. Heterotrimeric G protein The general function of Gi/o/z/t is to activate intracellular signaling pathways in response to activation of cell surface G protein-coupled receptors (GPCRs). GPCRs function as part of a three-component system of receptor-transducer-effector. The transducer in this system is a heterotrimeric G protein, composed of three subunits: a Gα protein such as Giα, and a complex of two tightly linked proteins called Gβ and Gγ in a Gβγ complex. When not stimulated by a receptor, Gα is bound to GDP and to Gβγ to form the inactive G protein trimer. When the receptor binds an activating ligand outside the cell (such as a hormone or neurotransmitter), the activated receptor acts as a guanine nucleotide exchange factor to promote GDP release from and GTP binding to Gα, which drives dissociation of GTP-bound Gα from Gβγ. GTP-bound Gα and Gβγ are then freed to activate their respective downstream signaling enzymes. Gi proteins primarily inhibit the cAMP dependent pathway by inhibiting adenylyl cyclase activity, decreasing the production of cAMP from ATP, which, in turn, results in decreased activity of cAMP-dependent protein kinase.
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Concepts associés (36)
G beta-gamma complex
The G beta-gamma complex (Gβγ) is a tightly bound dimeric protein complex, composed of one Gβ and one Gγ subunit, and is a component of heterotrimeric G proteins. Heterotrimeric G proteins, also called guanosine nucleotide-binding proteins, consist of three subunits, called alpha, beta, and gamma subunits, or Gα, Gβ, and Gγ. When a G protein-coupled receptor (GPCR) is activated, Gα dissociates from Gβγ, allowing both subunits to perform their respective downstream signaling effects.
Gs alpha subunit
DISPLAYTITLE:Gs alpha subunit The Gs alpha subunit (Gαs, Gsα) is a subunit of the heterotrimeric G protein Gs that stimulates the cAMP-dependent pathway by activating adenylyl cyclase. Gsα is a GTPase that functions as a cellular signaling protein. Gsα is the founding member of one of the four families of heterotrimeric G proteins, defined by the alpha subunits they contain: the Gαs family, Gαi/Gαo family, Gαq family, and Gα12/Gα13 family. The Gs-family has only two members: the other member is Golf, named for its predominant expression in the olfactory system.
Protéine G inhibitrice
Les protéines G inhibitrice (ou Gi) sont une des familles principales des protéines G associées à un récepteur. Il s'agit entre autres du récepteur muscarinique à l'acétylcholine, situé au niveau des muscles cardiaques. Ces récepteurs sont constitués de 3 sous-unités respectivement appelées α, β, γ. Mais seule la première est capable de fixer une molécule de GDP (guanosine diphosphate) ou GTP (guanosine triphosphate).
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