Cryo-EM Structures of Brain-Derived G Protein-Coupled Receptors: The First Direct Visualization from Mammalian Brain...

Area of Science:

• Neuroscience
• Molecular Biology
• Structural Biology

Background:

• Metabotropic glutamate receptors (mGluRs) are crucial for brain function, including synaptic plasticity, learning, and memory.
• Current structural and dynamic understanding of mGluRs and other G protein-coupled receptors (GPCRs) primarily comes from in vitro studies using engineered systems.
• Investigating endogenous receptor complexes is vital for understanding their native function and for therapeutic development.

Purpose of the Study:

• To determine the structural organization and dynamics of endogenous metabotropic glutamate receptor 2 (mGluR2)-containing assemblies in the mouse brain.
• To visualize and characterize distinct native receptor complexes, including their active and inactive states, and oligomeric forms.
• To provide a structural framework for the therapeutic targeting of mGluR2.

Main Methods:

• Utilized CRISPR-mediated protein tagging for precise labeling of endogenous proteins.
• Employed proteomics to identify associated proteins within receptor complexes.
• Applied rapid immunoaffinity purification and cryo-electron microscopy (cryo-EM) to isolate and visualize native mGluR2 assemblies.

Main Results:

• Identified at least 11 distinct endogenous mGluR2-containing receptor assemblies, encompassing various conformational and oligomeric states.
• Found mGluR2 homodimers and mGluR2/3 heterodimers as major endogenous species, with heterodimers observed only in active states.
• Revealed endogenous ternary complexes of mGluR2 homodimers or mGluR2/3 heterodimers with Gα_oA heterotrimers, differing from previously reported structures.

Conclusions:

• Elucidated the endogenous conformational, proteomic, and compositional landscape of heterogeneous mGluR2 complexes in the brain.
• Demonstrated significant differences between native brain structures and those obtained from recombinant systems.
• Established a structural foundation for developing targeted therapeutics for mGluR2-related neurological conditions.