The lower plot presents equivalent ECD fragmentation data for the apo, melittin, and CaMKII 290-309 bound calmodulin (outer to inner circles, respectively). It should be noted that the apo form here contains fewer fragments than the corresponding data in the upper panel, as a lower charge state (+8) was used. The PDB structure for the canonical calmodulin-ligand complex (1C1M) is shown in the center of the circle along with the fragment sites (purple) obtained from each ligand-bound experiment.