X-ray structure of dopamine transporter elucidates antidepressant mechanism

Antidepressants targeting Na+/Cl−-coupled neurotransmitter uptake define a key therapeutic strategy to treat clinical depression and neuropathic pain. However, identifying the molecular interactions that underlie the pharmacological activity of these transport inhibitors, and thus the mechanism by which the inhibitors lead to increased synaptic neurotransmitter levels, has proven elusive. Here we present the crystal structure of the Drosophila melanogaster dopamine transporter at 3.0 Å resolution bound to the tricyclic antidepressant nortriptyline. The transporter is locked in an outward-open conformation with nortriptyline wedged between transmembrane helices 1, 3, 6 and 8, blocking the transporter from binding substrate and from isomerizing to an inward-facing conformation. Although the overall structure of the dopamine transporter is similar to that of its prokaryotic relative LeuT, there are multiple distinctions, including a kink in transmembrane helix 12 halfway across the membrane bilayer, a latch-like carboxy-terminal helix that caps the cytoplasmic gate, and a cholesterol molecule wedged within a groove formed by transmembrane helices 1a, 5 and 7. Taken together, the dopamine transporter structure reveals the molecular basis for antidepressant action on sodium-coupled neurotransmitter symporters and elucidates critical elements of eukaryotic transporter structure and modulation by lipids, thus expanding our understanding of the mechanism and regulation of neurotransmitter uptake at chemical synapses. The X-ray crystal structure of the Drosophila dopamine transporter bound to the antidepressant drug nortriptyline is presented, providing the first crystal structure of a eukaryotic neurotransmitter sodium symporter. The dopamine transporter (DAT) is a membrane protein that removes the neurotransmitter dopamine from the synaptic cleft and imports it into the cytosol of surrounding cells, thereby terminating the signal of the neurotransmitter. Eric Gouaux and colleagues report the X-ray structure of the Drosophila DAT bound to the tricyclic antidepressant nortriptyline. This is the first crystal structure of a eukaryotic neurotransmitter sodium symporter to have been determined. The overall structure of Drosophila DAT is similar to that of LeuT, but the authors identify several differences that may have important roles in the transport mechanism of the eukaryotic protein and its regulation by phosphorylation.