Regulation of Oligomeric Organization of the Serotonin 5-HT2C Receptor Observed by Spatial Intensity Distribution Analysis [Molecular Biophysics]

March 30th, 2015 by Ward, R. J., Pediani, J. D., Godin, A. G., Milligan, G.

The questions of whether G proteincoupled receptors exist as monomers, dimers and/or oligomers and if these species interconvert in a ligand-dependent manner are amongst the most contentious current issues in biology. When employing Spatial Intensity Distribution Analysis to laser scanning confocal microscope images of cells stably expressing either a plasma membraneassociated form of monomeric eGFP or of a tandem of this fluorophore, the eGFP-tandem was identified as a dimer. Similar studies on cells stably expressing an eGFP-tagged form of the Epidermal Growth Factor receptor demonstrated that although largely a monomer in the basal state this receptor rapidly became predominantly dimeric upon addition of its ligand Epidermal Growth Factor. In cells induced to express an eGFPtagged form of the serotonin 5-HT2C receptor global analysis of construct quantal brightness was consistent with the predominant form of the receptor being dimeric. However, detailed Spatial Intensity Distribution Analysis demonstrated the presence of multiple forms ranging from monomers to higher-order oligomers. Furthermore, treatment with chemically distinct 5-HT2C receptor antagonists resulted in a time-dependent change in the quaternary organization to one in which there was a preponderance of receptor monomers. This antagonist-mediated effect was reversible, as washout of the ligand resulted in the regeneration of many of the oligomeric forms of the receptor.
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