Selective role of G protein gamma subunits in receptor interaction.
Receptor stimulation of nucleotide exchange in a heterotrimeric G protein (alphabetagamma) is the primary event-modulating signaling by G proteins. The molecular mechanisms at the basis of this event and the role of the G protein subunits, especially the betagamma complex, in receptor activation are unclear. In a reconstituted system, a purified muscarinic receptor, M2, activates G protein heterotrimers alphai2beta1gamma5 and alphai2beta1gamma7 with equal efficacy. However, when the alpha subunit type is substituted with alphao, alphaobeta1gamma7 shows a 100% increase in M2-stimulated GTP hydrolysis compared with alphaobeta1gamma5. Using a sensitive assay based on betagamma complex stimulation of phospholipase C activity, we show that both beta1gamma5 and beta1gamma7 form heterotrimers equally well with alphao and alphai. These results indicate that the gamma subunit interaction with a receptor is critical for modulating nucleotide exchange and is influenced by the subunit-type composition of the heterotrimer.
Hou
Y
Y
Departments of Anesthesiology and Genetics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Azpiazu
I
I
Smrcka
A
A
Gautam
N
N
D016367:Baculoviridae / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000502:physiology*; D006868:Hydrolysis; D007700:Kinetics; D011485:Protein Binding; D043585:Receptor, Muscarinic M2; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism
D043585:Receptor, Muscarinic M2; D011956:Receptors, Cell Surface; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D020962:Heterotrimeric GTP-Binding Proteins