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Both alpha1aAR and alpha1bAR form homo-oligomers with similar transfer efficiency of approximately 0.10 in BRET. Hetero-oligomers is also observed between alpha1bAR and alpha1aAR subtypes but not between alpha1bAR and beta2AR, NK1 tachykinin, or CCR5 chemokine receptors. Helix I and, to a lesser extent, helix VII play a role in the alpha1bAR homo-oligomerization. Agonist epinephrine or inverse agonist prazosin do not influence the oligomerization. A constitutively active (A293E) as well as a signaling-deficient (R143E) mutant of alpha1bAR oligomerize in the similar manners as those of the wild type alpha1bAR. Confocal imaging revealed that oligomerization of the alpha1AR subtypes correlated with their ability to co-internalize upon exposure to the agonist. Oxymetazoline (alpha1aAR selective agonist) induces the cointernalization of the alpha1aAR and alpha1bAR, whereas the alpha1bAR does not cointernalize with the NK1 tachykinin or CCR5 chemokine receptors. |