Target recognition by calmodulin: the role of acid region contiguous to the calmodulin-binding domain of calcineurin A

Small-angle X-ray scattering was used to investigate the role of acid region contiguous to the calmodulin-binding domain (391–414) of calcineurin in the target recognition by calmodulin. Three synthetic peptides with the residues 385–414, 380–414 and 374–414 of calcineurin A were used for this aim. The X-ray data are consistent with the fact that calmodulin binds all three peptides with or without Ca 2+. Without Ca 2+, the whole peptide including acid residues interacts with dumbbell shaped calmodulin, while the acid region is extruded from globular shaped calmodulin with Ca 2+. Consequently, a conformation of sequence 374–414 in calcineurin might be changed by Ca 2+-signal via calmodulin, suggesting the consequence of this region with acid residues in the full activation mechanism of calcineurin by Ca 2+-bound calmodulin.