Thermodynamics of apocalmodulin and nitric oxide synthase II peptide interaction.

ABSTRACT

The Ca2+-free form of calmodulin (CaM), apocalmodulin (ApoCaM), regulates a variety of target proteins including nitric oxide synthase II (NOS-II). The CaM-binding site of NOS-II can bind ApoCaM with high affinity. Substitution of hydrophobic amino acids by charged amino acids at crucial positions 3, 9 and 13 within the CaM-binding motif did not abolish the ApoCaM interaction that occurred with significant affinity, though the affinity of the interaction was decreased remarkably. Isothermal titration calorimetry revealed that interaction of ApoCaM and synthetic NOS-II peptides was driven entropically.