1CFD:
reference: Solution structure of calcium-free calmodulin., Kuboniwa H, Tjandra N, Grzesiek S, Ren H, Klee CB, Bax A, Nat Struct Biol 1995 Sep;2(9):768-76. PMID: 7552748

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).