The C-terminal Half-molecular Domain of Calmodulin is Responsible for High-affinity Interaction with Target Enzymes.

Abstract

Chimeric proteins from chicken and yeast calmodulin were prepared, and roles of three structural domains, N-domain (1-72), central helix (73-87) and C-domain (88-148), were evaluated. Mutants with the chicken-type C-domain activated the cyclic nucleotide phosphodiesterase with small values of Kact (the concentration of calmodulin giving a half maximal activation), a property of chicken calmodulin. On the other hand mutants with the yeast-type C-domain activated the phosphodiesterase with μM range of Kact, a property of yeast calmodulin. In activation of myosin light chain kinase, introduction of the yeast-type C-domain into chicken calmodulin increased the Kact value by more than 1000-fold with a dramatic decrease in the maximum activity (Vmax). On the other hand introduction of the chicken-type C-domain led to a profile with lower Kact and higher Vmax. Minor effects on Vmax and Kact were observed by substitution of the central helix. Although various small contributions of the N-domain were observed, a common role of the chicken-type C-domain was suggested to catch and maintain the high-affinity interaction with target enzymes.