CALCIUM-INDUCED STRUCTURAL-CHANGES AND DOMAIN AUTONOMY IN CALMODULIN

We have determined the solution structures of the apo and (Ca2+)(2) fo rms of the carboxy-terminal domain of calmodulin using multidimensiona l heteronuclear nuclear magnetic resonance spectroscopy, The results s how that both forms adopt well-defined structures with essentially equ al secondary structure, A comparison of the structures of the two form s shows that Ca2+ binding causes major rearrangements of the secondary structure elements with changes in inter-residue distances of up to 1 5 Angstrom and exposure of the hydrophobic interior of the four-helix bundle, Comparisons with previously determined high-resolution X-ray s tructures and models of calmodulin indicate that this domain is struct urally autonomous.