1D1O:
reference: Site-site communication in the EF-hand Ca2+-binding protein calbindin D9k., Maler L, Blankenship J, Rance M, Chazin WJ, Nat Struct Biol 2000 Mar;7(3):245-50. PMID: 10700285

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