If you look closely at the image below, you can see water molecules doing the twist. The dance is the highlight of a revealing look at the complex machinery a cell uses to exchange water with its environment.
Aquaporin channels provide a conduit for water to cross the cell membrane, but they somehow prevent smaller particles, like protons, from getting through. To understand this selectivity, computational biophysicists Emad Tajkhorshid and Klaus Schulten of the University of Illinois, Urbana- Champaign, constructed one of the largest atomic simulations ever attempted. The group assembled four membrane-bound aquaporin channels from more than 55,000 digital atoms and then added virtual water.
The winning illustration is a snapshot of the simulation in progress. Boomerang-shaped water molecules flip as they march single file through the narrow pore of the gold aquaporin, while the red balls and fibers that make up the cell's membrane keep the outside water (top) from mixing with the cellular pool (bottom). The display allowed the researchers to crack the mystery of aquaporin's discriminating tastes. "The flipping of the water molecules prevents protons from hopping through the pore," says Tajkhorshid, who notes that this novel mechanism of selectivity could not have been determined using traditional experimental methods.
"This is an almost-perfect use of existing [protein-modeling] software," says panel of judges member Felice Frankel. "It intelligently combines many of the methods used to represent proteins while successfully expressing a larger scientific idea." Plus, she says, "it's also very beautiful."
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