Atomic-level insights into metabolite recognition and specificity of the SAM-II riboswitch

The sulfur atom acts as the major anchor point and is involved in the key interactions. (A) Detailed view of the binding pocket of SAM-II with the ligand bound showing the distance (dotted lines) between the sulfur atom on SAM/SAH and O4 oxygens on the bases U11 and U21. (B) Probability distributions of the average distance between the sulfur atom and the two O4s when (S,S)-SAM (blue), (R,S)-SAM (green), or SAH (red) is bound to SAM-II.