Chaperones contribute to G protein coupled receptor oligomerization, but do not participate in assembly of the G protein with the receptor signaling complex.

Background: Previous studies have demonstrated that seven transmembrane receptors (7TM-Rs) can associate with various chaperones to control their maturation and export. It has been shown for a few years now that 7TM-Rs can form homo or heterooligomeric complexes. Due to the difficulty to study heterooligomers in a context devoid of homooligomers signaling, very little is known on heterooligomerization. β2AR-AT1R receptor complexes have been found on cells and ligand activation of one receptor affects signaling of the partner. Yet, very little is known about the mechanisms linking those receptors together. We propose to examine the role of chaperones in the maturation of homo- and heterodimers of the β2AR and AT1R. It would not be surprising that strict cellular mechanisms exist to ensure that only properly folded receptors are inserted into the plasma membrane.

Results: Our goal is to understand the process whereby the adrenergic and angiotensin receptors attain their proper mature conformation. We determined whether any of the common chaperones are physically associated with the fully and/or immature β2AR and AT1R receptors forms and if they play any role in the selective recruitment of G proteins subunits to receptor complexes. Our results suggest that when a pair of receptors is expressed in such way that one is retained in the endoplasmic reticulum (ER), this immature receptor will dictate the chaperones interacting with the receptor complex. We showed that ERp57 is important for receptor dimerization of AT1R homo and β2AR/AT1R receptor dimers, but plays no role in the β2AR homodimerization. Then, we verified if some of those chaperones could play a role in the assembly of the heterotrimeric G protein subunits with the receptor complex, but none appeared to be essential.

Conclusions: Overall, our results suggest that variations among receptor oligomers occur early in the synthesis/maturation processes, and that chaperones will interact more specifically with some receptor pairs than others to allow the formation of certain receptor pairs, while others will contribute to the folding and maturation of receptors without any effect on receptor assembly within a signaling complex.