When the brain sends urgent, exciting news, the signal travels via a chemical called glutamate. For years, researchers have been searching for the protein that stuffs glutamate into envelopes so that its message can be delivered. Now, they've finally found it.
Among dozens of neurotransmitters--the brain chemicals that send messages from one neuron to another--two stand out as stars. GABA and glutamate are fast-acting and widespread; they send the basic "stop" and "go" signals, respectively, that other chemicals, such as dopamine and serotonin, mostly modulate.
In order to transport a message, however, all neurotransmitters have to be stuffed at high concentrations into bubbles called synaptic vesicles that can burst into the space between neurons. Proteins called vesicular transporters do the stuffing: They pump neurotransmitters into the bubbles. Until now, researchers had identified vesicular transporters for GABA and most other neurotransmitters, but the glutamate transporter had been elusive. Circumstantial evidence, however, placed one candidate at the scene.
To test whether that protein, now dubbed VGLUT1, was indeed responsible for ferrying glutamate into vesicles, a team led by Robert Edwards of the University of California, San Francisco, inserted the gene that codes for the protein into cells that are able to build mock vesicles (Science, 11 August, p. 957). Compared to vesicles without VGLUT1, those with the protein packed in two to four times as much glutamate.
It's too early to tell whether identifying the protein will help guide the development of drugs, but neurobiologist Marc Caron of Duke University says the finding is still a much-anticipated accomplishment. "It's been a long time coming," he says--decades, in fact, and many other teams had been on the protein's trail.
Robert Edwards's lab