title: Receptor- and nucleotide exchange-independent mechanisms for promoting G protein subunit dissociation.
abstract: Mechanisms for heterotrimeric G protein activation that do not rely on G protein coupled receptor activation are becoming increasingly apparent. We recently identified beta gamma subunit-binding peptides that we proposed bound to a "hot spot" on beta gamma subunits, stimulating G protein dissociation without stimulating nucleotide exchange and activating G protein signaling in intact cells. AGS3, a member of the activators of G protein signaling family of proteins, also activates G protein signaling in a nucleotide exchange-independent manner, and AGS3 homologues are involved in asymmetric cell division during development. Here we demonstrate that a consensus G protein regulatory (GPR) peptide from AGS3 and related proteins is sufficient to induce G protein subunit dissociation and that both the GPR and hot spot-binding peptides promote dissociation to extents comparable with a known G protein activator, AMF. Peptides derived from adenylyl cyclase 2 and GRK2 prevented formation of the heterotrimeric complex but did not alter the rate of alpha subunit dissociation from beta gamma subunits. These data indicate that these nucleotide exchange-independent G protein activator peptides do not simply compete for alpha interactions with beta gamma subunits, but actively promote subunit dissociation. Thus, we propose two novel mechanisms for nucleotide exchange independent activation of G protein signaling, one that involves conformational changes in the alpha subunit and one that involves conformational changes in the beta gamma subunits.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
authors.forename: Mousumi
authors.initials: M
authors.lastname: Ghosh
authors.forename: Yuri K
authors.initials: YK
authors.lastname: Peterson
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Lanier
authors.forename: Alan V
authors.initials: AV
authors.lastname: Smrcka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019921:Biotinylation; D002352:Carrier Proteins / Q000378:metabolism; D003001:Cloning, Molecular; D016384:Consensus Sequence; D005822:Genetic Vectors; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection
chemical_list: D002352:Carrier Proteins; C498913:Gpsm1 protein, rat; D010446:Peptide Fragments; D021122:Protein Subunits; D011994:Recombinant Proteins; D020962:Heterotrimeric GTP-Binding Proteins