Solution structures of calmodulin, a ubiquitous calcium-binding protein in all eukaryotic cells, and calmodulin-peptide complex have been studied by solution scattering techniques. Calmodulin in solution possesses an elongated dumbbell shape, generally consistent with the crystal structure. A target peptide, such as melittin, mastoparan or MLCK-I, induces a large, calciumdependent conformational change in calmodulin. The overall shape of calmodulin-peptide comlex is globular. Using of the deletion mutants of calmodulin, we have revealed that the central linker region retains a predominantly α-helical conformation even in solution. A twisting motion would be a key step for the flexibility, as well as the bending. The globular structure is not a only possible conformation for the calmodulin-peptide complex. Some peptides form dumbbellshaped complexes with calmodulin.
