( l for water to pass through. The res...)Membrane research opens window to benefits for plants, humans

The researchers theorize the gating activity is universal in all plant aquaporins, because sequencing has shown the gating loop to be conserved in them.

"Plant cells close their water channels in response to drought stress in order to preserve their water content," said Tajkhorshid, who also is assistant director of research of the Theoretical and Computational Biophysics Group at the U. of I. Beckman Institute for Advanced Science and Technology. "It is interesting that they can also protect themselves against water overflow under flooding conditions by closing the very same water channels. It is amazing that although distinct cellular signals are involved in these two types of closing events, both mechanisms are mediated through the same structural elements of the protein -- that is by plugging the cytoplasmic entrance of the channel with an eolongated intracellular loop."

By atomic scale, the structural difference between open and closed channels is telling. When open, the protein allows water to go through; when closed, its pore size is reduced by 2 angstroms, effectively closing the channel, the Swedish researchers reported.

The work taken together, Tajkhorshid said, is a landmark study in membrane channels. It addresses the mechanism of gating and regulation of plasma membrane proteins in full detail. "We could see how every single atom moves and how collective motions of a large number of atoms resulted in the opening of the channel," he said.

Aquaporins -- discovered in 1991 by Peter Agre, now vice chancellor for science and technology at Duke University Medical Center -- help cells adjust water content. So far 13 forms of aquaporins have been found in animals and another 35 in plants.

Previous work in Tajkorshid's lab has identified how water molecules line up in single file and move as if dancing through open water channels. In less than a second, billions of water molecules can
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Source:University of Illinois at Urbana-Champaign