Wang, H.; Weaver, M. G.; Carrillo, E.; Zheng, I.; Gu, W.; Khau, J.; Mondal, A. K.; Yanez, A.; O'Brien, E. S.; Jayaraman, V.; Twomey, E. C.

Dopamine is a neurotransmitter essential for cognition, and its dysregulation is associated with neurological diseases. Historically, dopamine has been understood to signal exclusively through metabotropic receptors. Delta-type ionotropic glutamate receptors (GluDs), which have recently been established as ligand-gated ion channels, are fundamental for synaptic maintenance, are implicated in neurological disorders, and co-localize with dopaminergic machinery. Here, we report that dopamine is a direct agonist of GluDs, eliciting ionotropic activity, as visualized by cryo-electron microscopy (cryo-EM), bilayer recordings, mutagenesis, and patch clamp recordings. Dopamine binds to the GluD ligand binding domain, inducing clamshell closure and channel activation through a distinct molecular interface. GluD channel activity is tightly regulated by G-proteins, which act as molecular switches to tune GluD activity: free G{beta}{gamma} inhibits ligand-gating, while G or inactive G-protein heterotrimers enable dopamine-induced GluD currents. This tuning of GluD activity by G-proteins is uncoupled in a point mutation associated with neurodegeneration. These findings expand mechanisms of neuronal dopaminergic signaling, uncover how G-proteins tune GluD channel activity, and provide a framework for targeting GluDs in neurological diseases.