Guanine nucleotide exchange factors (GEFs) are proteins or protein domains that activate monomeric GTPases by stimulating the release of guanosine diphosphate (GDP) to allow binding of guanosine triphosphate (GTP). A variety of unrelated structural domains have been shown to exhibit guanine nucleotide exchange activity. Some GEFs can activate multiple GTPases while others are specific to a single GTPase.
Guanine nucleotide exchange factors (GEFs) are proteins or protein domains involved in the activation of small GTPases. Small GTPases act as molecular switches in intracellular signaling pathways and have many downstream targets. The most well-known GTPases comprise the Ras superfamily and are involved in essential cell processes such as cell differentiation and proliferation, cytoskeletal organization, vesicle trafficking, and nuclear transport. GTPases are active when bound to GTP and inactive when bound to GDP, allowing their activity to be regulated by GEFs and the opposing GTPase activating proteins (GAPs).
GDP dissociates from inactive GTPases very slowly. The binding of GEFs to their GTPase substrates catalyzes the dissociation of GDP, allowing a GTP molecule to bind in its place. GEFs function to promote the dissociation of GDP. After GDP has disassociated from the GTPase, GTP generally binds in its place, as the cytosolic ratio of GTP is much higher than GDP at 10:1. The binding of GTP to the GTPase results in the release of the GEF, which can then activate a new GTPase. Thus, GEFs both destabilize the GTPase interaction with GDP and stabilize the nucleotide-free GTPase until a GTP molecule binds to it. GAPs (GTPase-activating protein) act antagonistically to inactivate GTPases by increasing their intrinsic rate of GTP hydrolysis. GDP remains bound to the inactive GTPase until a GEF binds and stimulates its release.
The localization of GEFs can determine where in the cell a particular GTPase will be active. For example, the Ran GEF, RCC1, is present in the nucleus while the Ran GAP is present in the cytosol, modulating nuclear import and export of proteins.
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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.
Guanosine diphosphate, abbreviated GDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside guanosine. GDP consists of a pyrophosphate group, a pentose sugar ribose, and the nucleobase guanine. GDP is the product of GTP dephosphorylation by GTPases, e.g., the G-proteins that are involved in signal transduction. GDP is converted into GTP with the help of pyruvate kinase and phosphoenolpyruvate. The hydrolysis of GTP to GDP is facilitated by GTPase enzymes, which utilize a conserved active site motif known as the GTPase-activating protein (GAP).
vignette|droite|300 px|Structure de la GTPase placentaire CDC42 liée au GDP. Les GTPases sont une classe importante d'enzymes qui catalysent l'hydrolyse de la guanosine triphosphate (GTP) pour donner une guanosine diphosphate (GDP) et un ion phosphate. La fixation du GTP est effectuée par un domaine très conservé dans l'évolution, appelé domaine G, caractéristique de l'ensemble de cette superfamille. Cette hydrolyse est en général couplée à un autre processus biologique, comme la transduction du signal dans la cellule.
Explore la signalisation cellulaire dans les cellules eucaryotes, en se concentrant sur les protéines G, le Ras et les tyrosine kinases des récepteurs.
Explore les bases et les structures des récepteurs couplés aux protéines G, couvrant les schémas de signalisation, les structures, le contexte historique, le ciblage des médicaments et les progrès récents.
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