text: Calmodulin's ability to recognize a tremendous range of target proteins is due in large part to its structural flexibility.  In addition to the flexibility of the central linker domain, the N- and C-domains undergo open-closed conformational cycling in the Ca-bound state.  Calmodulin also exhibits great structural variability, and undergoes considerable conformational fluctuations, when bound to targets. Moreover, the predominantly hydrophobic nature of binding between calmodulin and most of its targets allows for recognition of a broad range of target protein sequences.  Together, these features allow calmodulin to recognize some 300 target proteins exhibiting a variety of CaM-binding sequence motifs.