Researchers 'see' structure of open nicotinic acetylcholine io...( The neurotransmitter acetylcholine i...)

The neurotransmitter acetylcholine is an essential chemical communicator, carrying impulses from neurons to skeletal muscle cells and many parts of the nervous system. Now researchers at the University of Illinois have painstakingly mapped the interior of a key component of the relay system that allows acetylcholine to get its message across. Their findings, which appear in the current issue of Nature Structure & Molecular Biology, reveal how the muscle nicotinic acetylcholine receptor responds to a burst of acetylcholine on the surface of a cell.

The muscle nicotinic receptor is a neurotransmitter-gated ion channel. This gate regulates the flow of information, in the form of charged particles, or ions, across the cell membrane. Although normally closed, when the ion channel encounters acetylcholine or nicotine on the surface of the cell the interaction causes the gate to open, allowing positively charged ions (called cations) to flow into the cell.

Scientists have tried for decades to understand the mechanism that allows these channels to open. Using cryo-electron microscopy, in which samples frozen at extremely low temperatures are examined under an electron microscope, some researchers obtained images of the closed ion channel. Others used X-ray crystallography to image the closed-channel conformation. This technique involves crystallizing the protein, creating a lattice that reveals many details of its three-dimensional structure.

But until the Illinois team developed a new method for probing the interior of the open channel, no studies had been able to infer the structure of the open channel conformation in a living cell. The Illinois team was able to do this by exploiting electrical properties of these membrane proteins.

Much like the flow of electrons through an electrical wire, the flow of ions through a cell membrane is a current. In the 1970s, two German researchers developed a technique for measuring the curre
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