Mechanosensitive Ion Channels
Top view of a mechanosensitive channel |
The ability to perceive and react to different stimuli from the surrounding environment is essential for all living organisms. Mechanical forces produced by sound, gravity, or osmotic stress, among other stimuli, are sensed by organisms through various mechanisms that all involve mechanosensitive ion channels. These membrane proteins open in response to mechanical stimuli, generating an ionic current that eventually triggers an electrical signal. Mechanosensitive channels also play an essential protective role in lower organisms through regulation of cell volume under osmotic stress conditions.
These top and side views of a mechanosensitive channel called MscS embedded in the membrane of a cell were created by Marcos Sotomayor and Klaus Schulten of the University of Illinois at Urbana-Champaign's Theoretical and Computational Biophysics Group. They were simulated using with their NAMD software and visualized with their VMD software. The models include the channel, a large patch of membrane composed of POPC lipids, and sufficient water on both sides of the membrane to fully solvate the system. The combined system includes more than 220,000 atoms. The simulations were performed on NCSA's Linux clusters, with additional calculations on systems at the Pittsburgh Supercomputing Center.
Side view of a mechanosensitive channel |
These simulations are the first to examine the free dynamics of the protein in a membrane. They revealed expected and unexpected characteristics that are likely essential to the channel's function. Through an extensive series of multi-nanosecond simulations, the team observed, among other things: the intermittent permeation of water molecules through the channel, the channel's strong tendency to close under constant pressure conditions, and an increase in the size of the channel when surface tension is applied to the embedding membrane. Meanwhile, the large balloon-shaped cytoplasmic domain of MscS spontaneously diffused ions through its side openings rather than its bottom central opening.
Access Online | Posted 11-30-2004
