Allosteric communication between protomers of dopamine class A GPCR dimers modulates activation

Abstract

A major obstacle to understanding the functional importance of dimerization between Class A G protein-coupled receptors (GPCRs) has been the methodological limitation in achieving control of the identity of the components comprising the signaling unit. We have developed a functional complementation assay that enables such control and illustrate it for the human dopamine D2 receptor. The minimal signaling unit, two receptors and a single G protein, is maximally activated by agonist binding to a single protomer, which suggests an asymmetrical activated dimer. Inverse agonist binding to the second protomer enhances signaling, whereas agonist binding to the second protomer blunts signaling. Ligand-independent constitutive activation of the second protomer also inhibits signaling. Thus, GPCR dimer function can be modulated by the activity state of the second protomer, which for a heterodimer may be altered in pathological states. Our novel methodology also makes possible the characterization of signaling from a defined heterodimer unit.

Evidence for activity-regulated hormone-binding cooperativity across glycoprotein hormone receptor homomers

“…Asymmetric agonist binding to WT GPCRs is compatible with the current notion that assumes that activation of one GPCR protomer is not only sufficient, but may favour signal transduction within a GPCR complex 28,29,44 . Indeed, binding of an agonist to one protomer is able to activate a dopamine D2 receptor homomeric complex, and binding of an inverse agonism to the second site enhances signalling 28 .…”

“…Indeed, binding of an agonist to one protomer is able to activate a dopamine D2 receptor homomeric complex, and binding of an inverse agonism to the second site enhances signalling 28 . However, as reported by Han et al 28 , this asymmetry is not only observed with ligand-induced conformational selection but also beyond ligand-binding cooperativity, because agonist-independent activation in a constitutive receptor is enough to propagate an inhibitory effect to the partner receptor and decrease the efficacy of the homomeric complex. A clear case of an asymmetric binding mode has been dissected in chemokine receptor homo-and hetero-mers (reviewed in ref.…”

“…Importantly, we were able to demonstrate that, at least for TSHr, this allosteric regulation is present in a native system, where the receptor is expressed at its normal level and in its physiological environment. The possibility to make a GPCR homomer function with a single ligand molecule has been documented in other systems 28,29 .…”

G protein-coupled receptor-receptor interactions give integrative dynamics to intercellular communication

“…Of particular interest in this field are recent developments in protein-protein docking software that lead to the prediction of the possible binding sites between two molecules, allowing the formation of a stable complex (Simpson et al, 2010;Kaczor et al, 2015;Soni and Madhusudhan, 2017). Examples of this approach include the study of the lutropin receptor dimerization (Fanelli, 2007), studies aimed at characterizing the interaction interface in serotonin (5-HT) 4 (Bestel, 2005;Soulier et al, 2007) and rhodopsin complexes (Han et al, 2009), and the generation of models for the heterodimeric mGluR 2 -5-HT 2A complex (Bruno et al, 2009) and for the dopamine D 1 -D 2 receptor dimer ). -Molecular dynamics and coarse-grained simulations are one of the most versatile and widely applied computational techniques for the study of membrane proteins (Almeida et al, 2017), as they consider the tertiary structure of the studied proteins and can implement an energy landscape to estimate the molecular interactions, also accounting for the role of the lipid microenvironment.…”

Asymmetric perturbations of signalling oligomers

“…However, fluorescence labelling and radioligand binding have revealed only cis activation for chimeric heterodimers of rhodopsinlike leukotriene B 4 receptors (Damian et al, 2008). Asymmetric activation was reported for G protein-fused dopamine D 2 receptor homodimers via functional complementation experiments (Han et al, 2009). Agonist binding to a single protomer induced full activation.…”