D2 Dopamine Receptor Homodimerization Is Mediated by Multiple Sites of Interaction, Including an Intermolecular Interaction Involving Transmembrane Domain 4

Abstract

In this study, we examined the mechanisms of intermolecular interaction involved in D2 dopamine receptor dimer formation to develop an understanding of the quaternary structure of G protein-coupled receptors. The potential role of two mechanisms was investigated: disulfide bridges and hydrophobic interactions between transmembrane domains. D2 dopamine receptor oligomers were unaffected by treatment with a reducing agent; however, oligomers of the D1 dopamine receptor dissociated following a similar treatment. This observation suggested that other forces such as hydrophobic interactions were more robust in the D2 receptor than in the D1 receptor in maintaining oligomerization. To elucidate which transmembrane domains were involved in the intermolecular hydrophobic interactions, truncation mutants were generated by successive deletion of transmembrane domains from amino and/or carboxyl portions of the D2 dopamine receptor. Immunoblot analyses revealed that all the fragments were well expressed but only fragments containing transmembrane domain 4 were able to self-associate, suggesting that critical areas for receptor dimerization resided within this transmembrane domain. Disruption of the helical structure of transmembrane domain 4 in a truncated receptor capable of forming dimers interfered with its ability to self-associate; however, a similar disruption of the transmembrane domain 4 helix structure in the full-length receptor did not significantly affect dimerization. These results indicated that there are other sites of interaction involved in D2 receptor oligomer assembly in addition to transmembrane domain 4.

Novel identification of peripheral dopaminergic D2 receptor in male germ cells

“…1B), similar to that observed by some authors in other cell systems [Farooqui et al, 1992;Zawarynski et al, 1998;Lee et al, 2000;Scarselli et al, 2001]. This heterogeneity can be explained by homodimerization [Zawarynski et al, 1998;Guo et al, 2003;Lee et al, 2003] and heterooligomerization of the D2 receptor [Rocheville et al, 2000;Canals et al, 2003: Kearn et al, 2005. Immunoprecipitation detection analysis with a monoclonal antibody only detected a predominant broad band of an apparent molecular mass of 50 kDa that can correspond to both isoforms (Fig.…”

Dopamine D2-like Receptors Are Expressed in Pancreatic Beta Cells and Mediate Inhibition of Insulin Secretion

“…Indeed, dopamine receptors are able to homodimerize (47,48) and heterodimerize (49) with members of the same family or with another type of receptors. For instance, somatostatin type 5 receptors, which contribute to the regulation of glucose homeostasis and insulin sensitivity (50), can heterodimerize with D2 receptors, thereby enhancing functional activity (51).…”

Heteromeric Dopamine Receptor Signaling Complexes: Emerging Neurobiology and Disease Relevance

“…What has become increasingly evident is that the interface(s) between the receptors in homomeric complexes likely involves residues located in transmembrane domains (TM), such as TM4 and TM5, as has been shown for the D2 receptor (D2R) (Guo et al, 2003;Lee et al, 2003), the alpha(1b)-adrenoceptor (López-Giménez et al, 2007), the 5HT1A receptor (Gorinski et al, 2012), and the 5HT2C receptor (Mancia et al, 2008). These observations have also been supported by the recent crystal structure reported for the beta1-adrenergic receptor dimer (Huang et al, 2013) in a lipid membrane-like environment which showed two dimer interfaces, one involving TM1, TM2, helix 8 and extracellular loop 1, and the second involving TM4, TM5, intracellular loop 2, and extracellular loop 2.…”