Probing the activation-promoted structural rearrangements in preassembled receptor–G protein complexes

Abstract

Activation of heterotrimeric G proteins by their cognate seven transmembrane domain receptors is believed to involve conformational changes propagated from the receptor to the G proteins. However, the nature of these changes remains unknown. We monitored the conformational rearrangements at the interfaces between receptors and G proteins and between G protein subunits by measuring bioluminescence resonance energy transfer between probes inserted at multiple sites in receptor-G protein complexes. Using the data obtained for the alpha(2A)AR-G alpha(i1) beta1gamma2 complex and the available crystal structures of G alpha(i1) beta1gamma2, we propose a model wherein agonist binding induces conformational reorganization of a preexisting receptor-G protein complex, leading the G alpha-G betagamma interface to open but not dissociate. This conformational change may represent the movement required to allow nucleotide exit from the G alpha subunit, thus reflecting the initial activation event.

Structural basis for the specific inhibition of heterotrimeric G q protein by a small molecule

“…1 A and B). A large body of experimental evidence (16,(21)(22)(23)(24)(25) supports the importance of the rearrangement of the GTPase and helical domains of Gα to create the necessary route for GDP dissociation. In particular, two flexible interdomain linkers appear to act together as a hinge during the opening of the helical domain away from the GTPase domain.…”

Receptor sequestration in response to β-arrestin-2 phosphorylation by ERK1/2 governs steady-state levels of GPCR cell-surface expression

“…that detects the agonist-promoted separation of Gα i1 and Gγ 2 in intact cells (Fig. 1A) (32). CXCL12 induces a rapid decrease in BRET signal between Gα i1 -91RLucII and GFP10-Gγ 2 in cells coexpressing the unmodified CXCR4 and Gβ 1 (Fig.…”

Heterodimerization of the α and β isoforms of the human thromboxane receptor enhances isoprostane signaling

“…Several studies have demonstrated that G-proteins exist in a stable complex with their cognate receptor [23,24], suggesting that receptor-effector coupling is mediated through dynamic conformational changes. In accord with this concept, a specific ligand-receptor interaction may mediate agonist activation of one effector pathway, yet act as antagonist for alternate pathway [25], a property likely to be modulated by dimerization.…”