Top 10 clustered models of the C-lobe of apo-CaM_F90L, apo-CaM_F93L, and apo-CaM_F142L aligned to represent an ensemble of possible states showing compact distribution of helix 3 and Ca²⁺-binding site 4 regions. Ensembles of the aligned top 10 clusters of the C-lobe of apo-CaM_F90L (red; A), apo-CaM_F93L (yellow; B), and apo-CaM_F142L (purple; C). Helix 3 is shown in blue, and the Ca²⁺-binding site 4 is the loop immediately following helix 3 and is labeled. Lower panels are structures from the upper panels rotated 180° to the right around the y axis.