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Water Bipolar Arrangement in Aquaporins

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Human kidneys need to filter about a bathtub of water a day through cells that contain membrane channels made of proteins called aquaporins. Crystallographers from the University of California at San Francisco (R. Stroud and coworkers) that discovered the structure of one type of aquaporins, aquaglyceroporins, have teamed up with UIUC researchers to determine how these channels achieve their very high water throughput, yet prevent the cells' electrical potential from discharging by not permitting any flow of ions or conduction of protons. The team, combining 106,000 atom simulations using NAMD and crystallography, found that the channels achieve the impressive filtering function by conducting water single file and keeping the water molecules strictly oriented: water molecules enter the channel oxygen atom first and leave the channel oxygen atom last. Aquaporins are ubiquitous in mammals, plants, and bacteria and the finding, published recently in Science magazine, has implications for many biological functions as well as for human diseases, e.g., cataract of the eye, loss of hearing, or diabetes insipidus. (more, press release)