Structural Basis of Inhibition and Desensitization in Heteromeric Kainate Receptors

Area of Science:

• Neuroscience
• Structural Biology
• Molecular Pharmacology

Background:

• Kainate receptors (KARs) are crucial for excitatory neurotransmission in the central nervous system.
• KARs typically form heterotetramers, with GluK2 and GluK5 subunits being the most prevalent.
• Understanding KAR conformational dynamics is key to deciphering their function and developing targeted drugs.

Purpose of the Study:

• To determine the cryo-EM structures of GluK2/GluK5 KARs in various functional states.
• To elucidate the structural basis for subtype-specific inhibition by antagonists.
• To investigate the distinct roles of GluK2 and GluK5 subunits in KAR function and regulation.

Main Methods:

• Electron cryo-microscopy (cryo-EM) to resolve structures of GluK2/GluK5 KARs.
• Engineering of GluK2 and GluK5 mutants to alter antagonist binding affinity.
• Structural analysis of antagonist-bound receptor complexes.

Main Results:

• Apo and glutamate-bound structures revealed compact packing and extensive intersubunit interactions in heterotetrameric KARs, indicating reduced conformational flexibility.
• Engineered mutants demonstrated distinct binding modes for the antagonist UBP310 on GluK2 versus GluK5 subunits.
• Stabilizing GluK5 subunits effectively occluded the receptor pore, while antagonizing GluK2 subunits left the pore accessible.

Conclusions:

• Heterotetrameric KARs exhibit distinct conformational properties compared to homomeric receptors.
• Targeting GluK5 subunits provides a more effective approach for inhibiting KARs than targeting GluK2.
• These findings offer a structural basis for developing subunit-specific KAR therapeutics.