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.  Its strucure is essentially a "bundle" of three sets of coaxially stacked helices with lysine embedded within a five-way junction.

 

 

 

 

 

 

 

The unbound lysine riboswitch: PDB ID 

This structure represents the first published structure of the unliganded form of a riboswitch.  Notably, it is almost identical in structure to the bound form, demonstrating that the free state can at least transiently sample "bound-like" states.  This was the first evidence that riboswitches utilize a conformational selection binding mechanism, which has now been shown for a variety of other riboswitch families.