The protein Calmodulin with Calcium binding
Calcium: blue
alpha-Helices: orange
beta-sheets: green.
One can clearly see the helix-turn(sheet)-helix-structure of the four Ca²⁺-binding sites.
The picture is derived from Protein 1CLL in The Protein Data Base cópia arquivada at the Wayback Machine. The official citation is:
H.M. Berman, J. Westbrook, Z. Feng, G. Gilliland, T.N. Bhat, H. Weissig, I.N. Shindyalov, P.E. Bourne: The Protein Data Bank. Nucleic Acids Research, 28 pp. 235-242 (2000).

Picture created with the Public-Domain-Program RasMol by Mathias Klode (w:de:Benutzer:Lode).

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