Signaling by a non-dissociated complex of G protein βγ and α subunits stimulated by a receptor-independent activator of G protein signaling, AGS8.
Accumulating evidence suggests that heterotrimeric G protein activation may not require G protein subunit dissociation. Results presented here provide evidence for a subunit dissociation-independent mechanism for G protein activation by a receptor-independent activator of G protein signaling, AGS8. AGS8 is a member of the AGS group III family of AGS proteins thought to activate G protein signaling primarily through interactions with Gbetagamma subunits. Results are presented demonstrating that AGS8 binds to the effector and alpha subunit binding "hot spot" on Gbetagamma yet does not interfere with Galpha subunit binding to Gbetagamma or phospholipase C beta2 activation. AGS8 stimulates activation of phospholipase C beta2 by heterotrimeric Galphabetagamma and forms a quaternary complex with Galpha(i1), Gbeta(1)gamma(2), and phospholipase C beta2. AGS8 rescued phospholipase C beta binding and regulation by an inactive beta subunit with a mutation in the hot spot (beta(1)(W99A)gamma(2)) that normally prevents binding and activation of phospholipase C beta2. This demonstrates that, in the presence of AGS8, the hot spot is not used for Gbetagamma interactions with phospholipase C beta2. Mutation of an alternate binding site for phospholipase C beta2 in the amino-terminal coiled-coil region of Gbetagamma prevented AGS8-dependent phospholipase C binding and activation. These data implicate a mechanism for AGS8, and potentially other Gbetagamma binding proteins, for directing Gbetagamma signaling through alternative effector activation sites on Gbetagamma in the absence of subunit dissociation.
Yuan
Chujun
C
Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
Sato
Motohiko
M
Lanier
Stephen M
SM
Smrcka
Alan V
AV
D000818:Animals; D002474:Cell-Free System / Q000737:chemistry / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D054799:Phospholipase C beta; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D010738:Type C Phospholipases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
C508124:Fndc1 protein, rat; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D011994:Recombinant Proteins; D010738:Type C Phospholipases; C518033:PLCB1 protein, human; C518036:PLCB2 protein, human; D054799:Phospholipase C beta; C518035:Plcb1 protein, rat; C518038:Plcb2 protein, rat