Solution structure of a 32-residue peptide corresponding to the first calcium binding site in calmodulin by 2-D NMR spectroscopy

High resolution 2-D NMR studies are reported for a 32-residue synthetic peptide corresponding to the helix-loop-helix motif of the first calcium binding site of the native calmodulin. The peptide shows much reduced secondary structure in DMSO compared to its conformation in the native protein. There are two very short helical regions flanking the middle loop-region, the latter consisting of a few type I β turn structures. Circular dichroism (CD) studies on four peptides including the above system corresponding to calcium binding sites I and IV of the native calmodulin and their mutually loop-exchanged analogues in a structure forming mixed trifluoroethanol/water solvent show that the secondary structure and calcium binding affinities depend on the particular permutation/combination of the helices and loops. (author). 29 refs., 6 figs., 1 tab