Aluminum-induced conformational changes in calmodulin alter the dynamics of interaction with melittin

Studies were undertaken to examine the impact of aluminum-induced structural changes in bovine brain calmodulin on the protein's interface region with melittin, a model for calmodulin's target enzymes. Both steady-state and time-dependent fluorescence characteristics of the single tryptophanyl residue of melittin were employed to derive information on aluminum-related changes in the fluorophore's microenvironment. In the presence of stoichiometric amounts of aluminum ions, calmodulin's target region with melittin appears to be more polar than that with aluminum absent. As a result, upon association of melittin with aluminum-calmodulin, the enhancement of helical arrays is less pronounced. The fluorophore's average microenvironment also is modified such that its apparent lifetime is shortened when aluminum is present. In the presence of aluminum ions, the solvation structure of calmodulin is possibly changed, which may be unfavorable for a proper fit between calmodulin and target proteins.