The debate over how signals pass from the outside of a cell to the inside is a long-standing one, with some researchers suggesting that when a chemical such as nicotine binds to an ion channel protein on the cell surface, the protein starts a "conformational wave" that propagates a signal through the protein body to the cell membrane, Associate Professor Lin Chen said.

Instead, the Chen group's study of crystal structure suggests a simple mechanical role for sugar molecules attached to the surface of the receptor.

"They serve as the link between the neurotransmitter binding site and the membrane region where the gate is located," Chen said. "The sugar is kind of like a hinge. It's pulling the door open and closed."

Biologist Raymond Stevens of The Scripps Research Institute, who wasn't involved in the study, called the finding "a landmark accomplishment for the fields of structural biology and neuronal cell signaling" and said it might lead to improve drugs for such maladies as epilepsy, schizophrenia and depression.

The research is reported in the journal Nature Neuroscience.