CALCIUM-INDUCED CONFORMATIONAL TRANSITION REVEALED BY THE SOLUTION STRUCTURE OF APO CALMODULIN

The solution structure of Ca2+-free calmodulin has been determined by NMR spectroscopy, and is compared to the previously reported structure of the Ca2+-saturated form. The removal of Ca2+ causes the interhelical angles of four EF-hand motifs to increase by 36 degrees-44 degrees, This leads to major changes in surface properties, including the closure of the deep hydrophobic cavity essential for target protein recognition, Concerted movements of helices A and D with respect to B and C, and of helices E and H with respect to F and G ape likely responsible for the cooperative Ca2+-binding property observed between two adjacent EF-hand sites in the amino- and carboxy-terminal domains.