Lysine
The bound lysine riboswitch (green) superimposed upon the unbound riboswitch (orange). Note that the binding pockets conformation is nearly identical in both the liganded and unliganded forms.
Lysine riboswitch: PDB ID
The lysine riboswitch is one of the largest known riboswitches. ÌýIts strucure is essentially a "bundle" of three sets of coaxially stacked helices with lysine embedded within a five-way junction.
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The unbound lysine riboswitch: PDB IDÌý
This structure represents the first published structure of the unliganded form of a riboswitch. ÌýNotably, it is almost identical in structure to the bound form, demonstrating that the free state can at least transiently sample "bound-like" states. ÌýThis was the first evidence that riboswitches utilize a conformational selection binding mechanism, which has now been shown for a variety of other riboswitch families.