Nanobody-based sensors reveal a high proportion of mGlu heterodimers in the brain

Using nanobodies labeled with FRET fluorophores, the authors show the presence and activation of GPCR mGlu2 and mGlu4 dimers in mouse brain samples and reveal that mGlu2-mGlu4 is the major form of mGlu4-containing dimers outside the cerebellum. 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 Forster 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.

Automated summary

This study presents a method for determining the subunit composition of endogenous cell surface protein complexes using nanobody-based sensors. The authors demonstrate the presence and activation of GPCR mGlu2 and mGlu4 dimers in mouse brain samples, and reveal the prevalence of mGlu2-mGlu4 heterodimers in addition to mGlu2 and mGlu4 homodimers.