Living organisms are dependent on being able to adjust the water content in their cells. This is achieved by regulating the flow of water through the cell membrane.
Water is ‘turned on’ and ‘turned off’ by membrane proteins that function as water conduits and are called aquaporins. In the new issue of Nature, Professor Per Kjellbom and Associate Professor Urban Johanson, plant biochemists at Lund University, Sweden, describe how this takes place. The discovery is not only a breakthrough for pure science. It may also pave the way for a new type of drug and for new cosmetic products.
Peter Agre discovered the first aquaporin in 1992 in red blood cells and was awarded the 2003 Nobel Prize. Since then, 13 variants of aquaporin have been found in animals and humans and 35 in plants. There are thousands of these aquaporins in every cell membrane. Aquaporins contain a conduit that is so tiny that only a single water molecule at a time can pass through it. But this traffic can be lively indeed. In one second, several billion water molecules can get through. The direction of this water flow is contingent on the osmotic pressure. The water moves in a direction away from a low and toward a high concentration of salt and nutritional substances. But the conduit isn’t always open. The Lund scientists have found out how it opens and closes. This was done in collaboration with a team at Chalmers University of Technology in Göteborg, Sweden, under the direction of Richard Neutze, and with Emad Tajkhorshid at the University of Illinois.
“We have used yeast fungi to produce aquaporins,” says Per Kjellbom. With our method we can produce sufficient amounts of pure aquaporins to obtain the crystals needed for our analyses. It turns out that with the technology we used to crystallize aquaporins they were in the closed position. Previously it had only been possible to produce open aquaporins. This gave us an opportunity to compare open and closed aquaporins and to understand how this opening and closing works at the molecular level.