Membrane proteins, including ion channels, receptors and transporters, are often composed of multiple subunits and can form large complexes. Their specific composition in native tissues is difficult to determine and remains largely unknown. In this study, we developed a method for determining the subunit composition of endogenous cell surface protein complexes from isolated native tissues. Our method relies on nanobody-based sensors, which enable proximity detection between subunits in time-resolved Förster resonance energy transfer (FRET) measurements. Additionally, given conformation-specific nanobodies, the activation of these complexes can be recorded in native brain tissue. Applied to the metabotropic glutamate receptors in different brain regions, this approach revealed the clear existence of functional metabotropic glutamate (mGlu)2–mGlu4 heterodimers in addition to mGlu2 and mGlu4 homodimers. Strikingly, the mGlu4 subunits appear to be mainly heterodimers in the brain. Overall, these versatile biosensors can determine the presence and activity of endogenous membrane proteins in native tissues with high fidelity and convenience.

膜蛋白，包括离子通道、受体和转运蛋白，通常由多个亚基组成，可以形成大的复合物。它们在天然组织中的具体组成很难确定，并且在很大程度上仍然未知。在这项研究中，我们开发了一种从分离的天然组织中确定内源性细胞表面蛋白复合物的亚基组成的方法。我们的方法依赖于基于纳米体的传感器，该传感器能够在时间分辨的 Förster 共振能量转移 (FRET) 测量中实现亚基之间的接近检测。此外，给定构象特异性纳米抗体，这些复合物的激活可以记录在天然脑组织中。应用于不同脑区的代谢型谷氨酸受体，这种方法揭示了除了 mGlu2 和 mGlu4 同源二聚体之外，功能性代谢型谷氨酸 (mGlu)2-mGlu4 异源二聚体的明确存在。引人注目的是，mGlu4 亚基似乎主要是大脑中的异二聚体。总体而言，这些多功能生物传感器可以高保真度和方便地确定天然组织中内源性膜蛋白的存在和活性。