Calcium-induced structural changes and domain autonomy in calmodulin

We have determined the solution structures of the apo and (Ca2+)(2) forms of the carboxy-terminal domain of calmodulin using multidimensional heteronuclear nuclear magnetic resonance spectroscopy, The results show that both forms adopt well-defined structures with essentially equal secondary structure, A comparison of the structures of the two forms shows that Ca2+ binding causes major rearrangements of the secondary structure elements with changes in inter-residue distances of up to 15 Angstrom and exposure of the hydrophobic interior of the four-helix bundle, Comparisons with previously determined high-resolution X-ray structures and models of calmodulin indicate that this domain is structurally autonomous.