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EPR-MD Refinement

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The environment of cells can undergo drastic changes, for example from dry to wet, in which case cells shrivel or swell. However, they are protected from bursting by a system of safety valves in their cellular membranes that open and release cellular content. Some of the valves open already at low membrane tension, but only little, others open only at higher tension, but wide and without filtering outflow. The mechanosensitive channel of small conductance, MscS, is a low pressure safety valve in bacterial cells (see the Feb 2007 highlight, "Observing and Modeling a Crucial Membrane Channel", the May 2006 highlight, "Electrical Safety Valve", and the Nov 2004 highlight, "Japanese Lantern Protein"). MscS is able to rescue cells about to burst by releasing small solutes through a large and transient opening in the cell membrane, thereby relieving internal pressure. The only way to learn how MscS performs this vital task is by determining its atomic-level structure under native conditions. However, the only structure available for MscS was obtained for the purified and crystallized protein; inspection of the structure left doubt that it shows a functional protein, i.e., a closed safety valve. Now a team of experimentalists and modelers report the structure of MscS seen in its natural membrane environment. In their approach, simulations incorporate information from so-called paramagnetic resonance measurements experiments. This finding is yet another case where the combination of modeling and observation offers entirely new close-up views of living cells (more on our MscS website).