Article Figures & Data
Figures
- Figure 1
Fluorescence resonance energy transfer. In this FRET example, cyan fluorescent protein (CFP) acts as the donor and yellow fluorescent protein (YFP) as the acceptor. When the two fluorophores are separated by a considerable distance, exposing the sample to light with the excitation frequency for CFP results in an emission spectrum corresponding to CFP only, with no contribution from the acceptor (top). When the two fluorophores are nearby (typically in the range of 10 to 100 Å), exposing the sample to the same light results in a nonradiative energy transfer from CFP to the nearby YFP acceptor, causing YFP to emit at its emission frequency (bottom). At the same time, due to the transfer of energy, emission from CFP is considerably reduced. Detection of YFP emission indicates that fluorescence resonance energy transfer has occurred between the two fluorophores as a result of their close proximity. By fusing these fluorophores to the receptors of interest, dimerization can be implied if fluorescence resonance energy transfer is observed.
- Figure 2
Dimerization between D1R and GHSR1a. When dimerized with D1R, GHSR1a switches G-protein coupling from Gq/11 to Gi/o. Coadministration of a D1R agonist with a GHSR1a agonist leads to a fourfold amplification of D1R-associated cAMP accumulation. It is believed that the Gβγ subunit associated with GHSR1a adopts a stimulatory role on adenylyl cyclase activity due to the proximity of the αS subunit derived from D1R’s trimeric G-protein.
- Figure 3
Dimerization between D2R and GHSR1a. Proposed signaling through D2R involves coupling to a Gi pathway, which typically does not involve intracellular Ca2+ accumulation from the endoplasmic reticulum. Dimerization with GHSR1a, in the absence of a ghrelin ligand leads to a PLC-dependent accumulation of Ca2+. D2R’s Gβγ subunit acts to stimulate PLC activity, and αi coupling by D2R is also required for Ca2+ accumulation. In contrast, Gαq activity associated with GHSR1a is not required for D2R-induced Ca2+ accumulation. It is believed that the D2R-GHSR1a dimer is responsible for the anorectic effects of D2R agonists such as cabergoline.
- Figure 4
Dimerization between MC3R and GHSR1a results in amplification of MC3R signaling and attenuation of GHSR1a signaling. While it is believed that the pathways involved are not changed, changes in the amplitude of the signals occur. Dimerization with stimulation of MC3R leads to a twofold amplification of MC3R-induced cAMP accumulation (top), while the GHSR1a protomer shows a ligand-dependent as well as ligand-independent 40% reduction in Ca2+ accumulation when dimerized with MC3R (bottom). Amplification of MC3R signaling appears to be dependent on GHSR1a’s constitutive activity.
- Figure 5
Dimerization between 5-HT2C and GHSR1a. When dimerized with 5-HT2C. GHSR1a displays a 65% reduction in ghrelin-induced Ca2+ accumulation, with this effect not requiring the presence of a 5-HT2C ligand. While changes in serotonergic signaling associated with the dimer through 5-HT2C have not yet been observed, cross-desensitization, cross-sensitization, and cointernalization do occur.
- Figure 6
Selected areas of interest involving possible GHSR1a dimers along with postulated roles/treatments. Brain figure adapted from the Allen Mouse Brain Atlas (Lein et al., 2007).
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