Molecule of the Month: Mechanosensitive Channels
Pressure-sensitive channels open when the internal pressure of a cell gets too high
Exploring the Structure
MscS (PDB entries 2oau and 2vv5)
You can see MscS in action in two PDB files: the closed form is shown on the left from PDB entry 2oau , and the open form is shown on the right from PDB entry 2vv5 . In both pictures, we are looking down the pore. Two leucine amino acids in each chain, shown in white, form a circular gate that blocks passage in the closed form. It may look like this ring of amino acids is open enough to allow passage, but since these amino acids are so hydrophobic, they actually block the movement of water molecules. This ring has been termed a "vapor seal" because of this resistance to wetting by water. You can click on the pictures here for an interactive Jmol version.
Topics for Further Discussion
- Several other membrane channels are composed of identical protein subunits arranged to form a tube. Can you find other examples in the PDB?
- The potassium channel is highly specific, allowing passage of potassium ions, whereas mechanosensitive channels allow passage of many types of ions and small molecules. What aspects of these structures lead to these different functional characteristics?
November 2008, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2008_11