The liganded receptor undergoes a conformational change, generating a signal that is propagated in a manner that is not completely understood to the the G-protein. This stimulates the exchange of GDP for GTP in the G-protein alpha subunit, activating the G-protein. This event is negatively regulated by some Activators of G protein signaling (AGS) proteins, a class of proteins identified in yeast functional screens for proteins able to activate G protein signaling in the absence of a G protein–coupled receptor (GPCR) (Cismowski et al. 1999, Takesono et al. 1999). AGS proteins contain G protein regulatory (GPR) motifs (also referred to as the GoLoco motif) that bind and stabilize the Galpha subunit in its GDP-bound conformation (Mochizuki et al. 1996, Peterson et al. 2000, Cao et al. 2004, Blumer & Lanier 2014). Some RGS proteins similarly bind to Galpha preventing the exchange of GDP for GTP (Soundararajan et al. 2008).
Van Dop, C, Apone, LM, Medynski, DC
Lerea, CL, Bunt-Milam, AH, Hurley, JB
Itoh, H, Tsukamoto, T, Kozasa, T, Matsuoka, M, Kaziro, Y, Toyama, R
Margolskee, RF, Getchell, TV, Takami, S, McLaughlin, SK, Getchell, ML
guanyl-nucleotide exchange factor activity of Ligand:GPCR complexes that activate Gi:Heterotrimeric G-protein Gi (inactive) [plasma membrane]
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