Elucidating the structure-function of the ionotropic delta receptor in the presence of trans-synaptic partners.

The ionotropic glutamate receptors (iGluRs) are glutamate-gated cationic channels expressed in the brain. They are known for their involvement in learning and memory, behavior, and motor coordination. The delta receptor is a member of the iGluR family due to its structural and sequence similarity. This receptor has been demonstrated to play a role in synaptic long-term depression, learning and memory, and implicated in neurological disorders like autism and schizophrenia. Although CryoEM structures show the formation of a pore-like structure like other iGluRs, the delta receptor does not demonstrate isolated ligand-gated currents like its family members, making it difficult to study their function. Our lab recently demonstrated the delta receptor is capable of glycine-gated activity when the extracellular domains come into closer proximity by using chemical linkers at the amino-terminal domain. Using FRET/FLIM, we further demonstrated that the delta receptor trans-synaptic partners, presynaptic Neurexin1β and soluble cerebellin, are capable of bringing the extracellular domains into closer proximity. Based on these findings, I developed a Neurexin1β dimer complex using two different coiled tags at the carboxyl-terminal domain and tagged them with separate purification tags for co-immunoprecipitation. Using this Neurexin1β dimer complex in conjunction with cerebellin, we are capable of inducing glycine-gated activity in single channel patch recordings. Furthermore, using this Neurexin1β dimer complex, I have started investigating the conformational effects of Neurexin1β on the delta receptor using single molecule FRET, and have begun to uncover the conformational landscape of the extracellular domains when in the presence and absence of glycine and the Neurexin1β/cerebellin dimer complex. The findings obtained from these studies will further elucidate the required structure and conformational changes for delta receptor activity, and reduce the challenges of targeting the ionotropic activity of the delta receptor.