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Dopamine D<inf>4</inf> receptor oligomerization - Contribution to receptor biogenesis

Abstract:

Dopamine D4 receptors (D4Rs) are G protein-coupled receptors that play a role in attention and cognition. In the present study, we investigated the dimerization properties of this receptor. Western blot analysis of the human D4.2R, D4.4R and D4.7R revealed the presence of higher molecular weight immunoreactive bands, which might indicate the formation of receptor dimers and multimers. Homo- and heterodimerization of the receptors was confirmed by co-immunoprecipitation and bioluminescence resonance energy transfer studies. Although dimerization of a large number of G protein-coupled receptors has been described, the functional importance often remains to be elucidated. Folding efficiency is rate-limiting for D4R biogenesis and quality control in the endoplasmic reticulum plays an important role for D4R maturation. Co-immunoprecipitation and immunofluorescence microscopy studies using wild-type and a nonfunctional D4.4R folding mutant show that oligomerization occurs in the endoplasmic reticulum and that this plays a role in the biogenesis and cell surface targeting of the D4R. The different polymorphic repeat variants of the D4R display differential sensitivity to the chaperone effect. In the present study, we show that this is also reflected by bioluminescence resonance energy transfer saturation assays, suggesting that the polymorphic repeat variants have different relative affinities to form homo- and heterodimers. In summary, we conclude that D4Rs form oligomers with different affinities and that dimerization plays a role in receptor biogenesis. © 2011 The Authors Journal compilation © 2011 FEBS.