(A) Movement of the mouse CaMKII-α hub (PDB code: 1HKX) along the lowest-frequency internal normal mode recapitulates the structural differences in the S. rosetta hub. Normal modes were calculated using a vertical dimer from the mouse CaMKII-α hub, using an elastic network model (Suhre and Sanejouand, 2004). In the diagram on the left, displacement vectors corresponding to the lowest-frequency internal normal mode are shown by arrows. The structures shown in magenta and blue correspond to excursions of the mouse hub along this mode. In the middle, the structures of the mouse hub and the S. rosetta hub are compared, and the arrows show the displacement vectors between the two structures. The diagram on the right shows the structures of the mouse hub and the S. rosetta hub, and excursions of the mouse hub along the lowest-frequency internal normal mode (green). Note that the normal mode, calculated without reference to the S. rosetta structure, captures the essential features of the structural difference between the mouse and S. rosetta hub. (B) Comparison of the S. rosetta hub structure to instantaneous structures from a molecular dynamics trajectory for a decameric human hub assembly (the open decameric assembly is generated by removing a vertical dimer from the dodecameric hub ring; PDB code: 2UX0). Helices A to D in the S. rosetta hub are aligned to the corresponding helices in the instantaneous simulated structures. Three instantaneous structures from the trajectory, at 1, 7 and 41 ns, are shown. Note that the strands of the β-sheet in structures at 7 and 41 ns are closely aligned with the S. rosetta structure.