Dual positive and negative regulation of GPCR signaling by GTP hydrolysis.
G protein-coupled receptors (GPCRs) regulate a variety of intracellular pathways through their ability to promote the binding of GTP to heterotrimeric G proteins. Regulator of G protein signaling (RGS) proteins increases the intrinsic GTPase activity of Galpha-subunits and are widely regarded as negative regulators of G protein signaling. Using yeast we demonstrate that GTP hydrolysis is not only required for desensitization, but is essential for achieving a high maximal (saturated level) response. Thus RGS-mediated GTP hydrolysis acts as both a negative (low stimulation) and positive (high stimulation) regulator of signaling. To account for this we generated a new kinetic model of the G protein cycle where Galpha(GTP) enters an inactive GTP-bound state following effector activation. Furthermore, in vivo and in silico experimentation demonstrates that maximum signaling output first increases and then decreases with RGS concentration. This unimodal, non-monotone dependence on RGS concentration is novel. Analysis of the kinetic model has revealed a dynamic network motif that shows precisely how inclusion of the inactive GTP-bound state for the Galpha produces this unimodal relationship.
Smith
Benjamin
B
Molecular Organization and Assembly of Cells Centre, University of Warwick, Coventry, UK.
Hill
Claire
C
Godfrey
Emma L
EL
Rand
David
D
van den Berg
Hugo
H
Thornton
Steven
S
Hodgkin
Matthew
M
Davey
John
J
Ladds
Graham
G
D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism; D017353:Gene Deletion; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D010675:Pheromones / Q000378:metabolism; D020710:RGS Proteins / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
D044385:GTP-Binding Protein alpha Subunits; D010675:Pheromones; D020710:RGS Proteins; D043562:Receptors, G-Protein-Coupled; C489854:Rgs1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D006160:Guanosine Triphosphate