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Japanese lantern protein MscS

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Many bacteria hang into their cellular membranes proteins that look like a Japanese lantern. These proteins have a flexible cylinder (pore) that crosses the membrane and opens and closes depending on membrane tension; from the cylinder hangs a balloon with seven small openings around its equator (see figure). The apparent function of the Japanese lantern protein, aptly called mechanosensitive channel of small conductance (MscS), is to protect the bacterial cell against osmotic stress: when a bacterium finds itself suddenly in an aqueous environment entering water can burst the cell. Before this happens the cell membrane experiences tension that opens the protein pore, permitting passage of water and ions, the efflux being controlled through the protein balloon. A recent study explores the dynamical properties of MscS, e.g., pore closure and opening as well as ion conduction, by means of molecular dynamics simulations using NAMD. Embedding the large protein into a lipid bilayer and water led to a simulation encompassing 220,000 atoms. Surprisingly, the protein balloon was found to control the arrangement of positive and negative ions through a peculiar pattern of charged, polar, and non-polar amino acids on its internal and external surfaces. This suggests that the Japanese lantern protein has a yet unknown second function in the bacterial cell.