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Gating of Aquaporins

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Your favorite flower pot would not survive a weekend in your office without watering, if it wasn't for a sophisticated cellular mechanism evolved in land plants to conserve water under drought conditions. Water exchange between cells and their environment is facilitated by a group of highly specialized membrane proteins called aquaporins. Although present in all life forms, plants are particularly dependent on their function. While in most species these channels function as always-open "cellular pipes" allowing water in and out of the cell, in plants they evolved into "cellular faucets" whose water permeability can be controlled by the cell. Nearly all plant aquaporins can be gated in response to drought or even flooding conditions, through basic biochemical signals, e.g., phosphorylation and change of pH. A recent Nature paper reporting a collaborative study between crystallographers who succeeded in solving the first structure of a plant aquaporin from spinach, and modelers provides the most detailed view of the mechanism of gating for a membrane channel. Molecular dynamics simulations of the channel performed by NAMD reveals a dual gating mechanism in which phosphorylation of certain protein residues unleashes a long cytoplasmic loop that physically blocks water access to the pore. More information on aquaporin research can be found here.