THE INTERACTION OF CYCLOSPORINE AND CALMODULIN

The interaction of cyclosporin A and dansyl cyclosporin A with bovine and wheat germ calmodulin has been monitored by measurements of induced changes in dansyl and bound toluidinyl naphthalene sulfonate fluorescence. The interaction is Ca2+‐dependent and 1 : 1 Measurements of the efficiency of radiationless energy transfer from bound dansyl cyclosporin A to an acceptor group located on Cys‐27 of wheat germ calmodulin suggest that the primary binding site is not located on the N‐terminal lobe (residues 1–65). However, studies with proteolytic fragments of calmodulin indicate that elements of the N‐terminal half‐molecule (residues 1–77) may be involved in the stabilization of the binding site. The binding of cyclosporin alters the physical properties of calmodulin and, in particular, reduces the localized rotational mobility of a fluorescent probe. Copyright © 1990 John Wiley & Sons, Inc.