Like the petals of a flower. Ion channels open and shut on a millisecond time scale and send thousands of charged ions flowing in or out of the cell to trigger or modulate nerve cell electrical activity, muscle contraction or tuning of “hair cells” in our inner ear.
Ion channels made by microbes as part of their competitive arsenal can be stunningly simple and highly effective: valinomycin, secreted by Streptomyces , is a circular ring of only 12 amino acids. (see: http://en.wikipedia.org/wiki/Valinomycin).
But ion channels in our cells are enormously large and complex because they need to be regulated in sophisticated ways, in response to small molecules, voltage or pH. One such type of potassium channel opens when calcium binds and closes when calcium comes off. To understand how this works, researchers from Rod McKinnon’s group crystallized and solved for the structure of these membrane proteins in multiple forms and put the story together in this movie.
First, you will see a ring of 4 blue protein domains, sitting on top of 4 red protein domains, which form the circular gate that regulates the opening of the channel. Morphing between the calcium bound and unbound structures shows how the ring changes shape.
Next, we zoom in on the calcium (yellow sphere) site. Finally, we see the gating ring assembled with the ion channel itself (green helices) which forms the K+ conducting pore through the membrane. Watch how the gating ring opens “like the petals of a flower” to tweak the channel open or closed. Thus, the free energy from calcium binding is converted into mechanical energy of opening (gating) the ion channel. This is poetry in motion!