For a decade, Roderick MacKinnon’s team has been in the forefront of figuring out how these amazing gatekeepers of the cell work (see 1/17/2002,  3/12/2002,  5/29/2002,  5/01/2003,8/05/2005, 12/02/2007).  Up till now, researchers have only seen the closed state of the gating ring.  MacKinnon’s team has imaged the tiny gate in the open condition for the first time, and found that looks like a flower with four petals opening up.  The abstract in Nature1 says:

Here we present the Ca2+-bound conformation of the gating ring. This structure shows how one layer of the gating ring, in response to the binding of Ca2+, opens like the petals of a flower. The degree to which it opens explains how Ca2+ binding can open the transmembrane pore.

The paper includes movies of how the structure works. Sure enough, calcium ions binding to specialized pockets in the gating ring cause a conformational change that looks for all the world like flower petals opening. The four “petals” rock upward and back, widening the channel enough for ions to pass through. The action is reversible. When the calcium concentration drops again, the petals fold and the channel closes.

They used the flowery metaphor again inside the paper: “Viewing an interpolative movie in which the Ca2+-free gating ring is morphed to the Ca2+-bound gating ring, it seems that Ca2+ binding causes the N-terminal lobes of the RCK1 units to ‘open up’ on the membrane-facing surface of the gating ring in a way akin to petals opening on a flower (Supplementary Movie 1, part 1).”….

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