Department of Pharmacology and Toxicology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia 30912-2300, USA.
Mol Pharmacol. 2013 Sep;84(3):346-52. doi: 10.1124/mol.113.086868. Epub 2013 Jun 18.
G protein-coupled receptors (GPCRs) transduce many important physiological signals and are targets for a large fraction of therapeutic drugs. Members of the largest family of GPCRs (family A) are thought to self-associate as dimers and higher-order oligomers, although the significance of such quaternary structures for signaling or receptor trafficking is known for only a few examples. One outstanding question is the physical stability of family A oligomers in cell membranes. Stable oligomers would be expected to move through cellular compartments and membrane domains as intact groups of protomers. Here, we test this prediction by recruiting subsets of affinity-tagged family A protomers into artificial microdomains on the surface of living cells and asking if untagged protomers move into these domains (are corecruited) at the same time. We find that tagged β₂ adrenergic and μ-opioid protomers are unable to corecruit untagged protomers into microdomains. In contrast, tagged metabotropic glutamate receptor protomers do corecruit untagged protomers into such microdomains, which is consistent with the known covalent mechanism whereby these family C receptors dimerize. These observations suggest that interactions between these family A protomers are too weak to directly influence subcellular location, and that mechanisms that move these receptors between subcellular compartments and domains must operate on individual protomers.
G 蛋白偶联受体（GPCRs）转导许多重要的生理信号，是很大一部分治疗药物的靶点。最大的 GPCR 家族（家族 A）的成员被认为可以自组装为二聚体和更高阶的寡聚体，尽管这种四级结构对信号转导或受体运输的意义仅在少数几个例子中有所了解。一个悬而未决的问题是家族 A 寡聚体在细胞膜中的物理稳定性。稳定的寡聚体预计会作为完整的原聚体通过细胞区室和膜域移动。在这里，我们通过将亲和标记的家族 A 原聚体亚群募集到活细胞表面的人工微域中来检验这一预测，然后询问未标记的原聚体是否同时进入这些域（被共同募集）。我们发现，标记的β₂肾上腺素能和μ-阿片样受体原聚体无法将未标记的原聚体共同募集到微域中。相比之下，标记的代谢型谷氨酸受体原聚体可以将未标记的原聚体共同募集到这种微域中，这与这些家族 C 受体通过共价机制二聚化的已知机制一致。这些观察结果表明，这些家族 A 原聚体之间的相互作用太弱，无法直接影响亚细胞位置，并且必须在单个原聚体上操作将这些受体在亚细胞区室和域之间移动的机制。
