Virtuelle (Nano) Welten: PDB Molecule of the Month 38: Potassium Channel

Open and Shut

Hundreds of different ion channels are made by living cells, for a variety of different functions. These all have similar filters, shown at the top in these two examples, connected to specialized gating domains, shown at the bottom. The membrane is shown schematically with a gray stripe and only two of the four chains are shown in the selectivity filters, so that you can see the pore. The gating domains open and shut the channel based on different signals, such as voltage or the presence of key signaling molecules. Several structural mechanisms are used for opening and closing potassium channels. In the two simple bacterial channels shown here, protein domains connected to the channel are thought to twist the four chains of the channel. This can be clearly seen by comparing the "open" channel structure of PDB entry 1lnq on the right with the "closed" structure of PDB entry 1k4c on the left (the gating domain of this structure is taken from the low resolution structure in 1f6g). The more complex channels found in nerve cells, which open and close after sensing changes in the voltage across the membrane, are thought to include a small tethered ball of protein that floats over and physically blocks the pore. (Note: somewhat surprisingly, the crystal structure of the closed channel has several potassium ions in the channel, shown here in green, but the structure of the open channel was solved without potassium ions.)

Potassium Channels

Open and Shut