Class-A G protein-coupled receptors (GPCRs) are known to homo-dimerize in the membrane. Yet, methods to characterize the structure of GPCR dimer in the native environment are lacking. Accordingly, the molecular basis and functional relevance of the class-A GPCR dimerization remain unclear. Here, we present the dimeric structural model of GPR17 in the cell membrane. The dimer mainly involves transmembrane helix 5 (TM5) at the interface, with F229 in TM5, a critical residue. An F229A mutation makes GPR17 monomeric regardless of the expression level of the receptor. Monomeric mutants of GPR17 display impaired ERK1/2 activation and cannot be properly internalized upon agonist treatment. Conversely, the F229C mutant is cross-linked as a dimer and behaves like wild-type. Importantly, the GPR17 dimer structure has been modeled using sparse inter-protomer FRET distance restraints obtained from fluorescence lifetime imaging microscopy. The same approach can be applied to characterizing the interactions of other important membrane proteins in the cell.

已知A类G蛋白偶联受体（GPCR）在膜中均二聚。然而，缺乏在天然环境中表征GPCR二聚体结构的方法。因此，A类GPCR二聚化的分子基础和功能相关性仍不清楚。在这里，我们介绍细胞膜中GPR17的二聚体结构模型。二聚体主要在界面处涉及跨膜螺旋5（TM5），TM5中的F229是关键残基。F229A突变使GPR17成为单体，而与受体的表达水平无关。GPR17的单体突变体显示受损的ERK1 / 2活化，并且在激动剂治疗后不能适当地内在化。相反，F229C突变体以二聚体形式交联，其行为类似于野生型。重要的，GPR17二聚体结构已使用从荧光寿命成像显微镜获得的稀疏前体间FRET距离限制进行建模。可以将相同的方法用于表征细胞中其他重要膜蛋白的相互作用。