The structure of apo-calmodulin. A 1H NMR examination of the carboxy-terminal domain.

The structure of the carboxy-terminal domain of bovine calmodulin, TR2C, in the calcium-free form was investigated using two-dimensional 1H NMR. Sequential resonance assignments were made using standard methods. Using information from medium and long range contacts revealed by nuclear Overhauser enhancement, the secondary structure and global fold were determined. The apo protein possesses essentially the same secondary structure as that in the calcium activated form of intact calmodulin. However, the secondary structural elements are rearranged so that the hydrophobic binding pocket is closed in the apo-form.