Ca2+-dependent high-affinity complex formation between calmodulin and melittin

Influence of temperature and denaturing agents on the structural stability of calmodulin. A 1H-nuclear magnetic resonance study

The structural stability of calmodulin was studied by 1H-nuclear magnetic resonance spectroscopy under different denaturing conditions. The presence of Ca2+ stabilizes the structural properties of the native protein. In the absence of calcium the structural integrity of calmodulin can easily be affected by elevated temperatures or by high concentrations of denaturing agents. The unfolding process under various denaturing conditions is reversible underlining the high degree of structural flexibility of this protein.

High affinity binding of the mastoparans by calmodulin

Calmodulin exhibits high affinity, calcium-dependent binding of the mastoparans--a group of cytoactive tetradecapeptides. The dissociation constants for the peptide-calmodulin complexes determined in 0.20 N KCl, 1.0 mM CaCl2, pH 7.3 are approximately 0.3 nM for mastoparan, approximately 0.9 nM for mastoparan X, and approximately 3.5 nM for Polistes mastoparan. The dissociation constant for the mastoparan-calmodulin complex is the smallest known for any calmodulin binding protein or peptide, suggesting that some type of peptide-calmodulin interaction could be physiologically significant.