On the mechanism of interaction between calmodulin and calmodulin-dependent proteins

Molecular and kinetic studies of the interaction between calmodulin and calmodulin-dependent proteins have been reviewed. Several calmodulin-dependent proteins have been purified to homogeneity and characterized in terms of subunit structure in recent years. The results indicate that these proteins do not contain a common subunit as the basis of calmodulin binding. A monoclonal antibody capable of interacting with several calmodulin-dependent proteins has been obtained, suggesting that these proteins contain common structure. It seems that hybridoma technology may be used for probing calmodulin-binding domains in the calmodulin-dependent proteins. Using a fluorescent-labelled cyclic nucleotide phosphodiesterase, the interaction between calmodulin and the enzyme in the absence of Ca2+ can be demonstrated, and the equilibrium constant of the reaction can be determined. The study further defines the multiple interactions in the activation of the cyclic nucleotide phosphodiesterase by Ca2+ and calmodulin. Previous kinetic results along with the present results are summarized and used to elucidate the regulatory significance of the multiple Ca2+-binding of calmodulin.