4AQR:
reference: A bimodular mechanism of calcium control in eukaryotes., Tidow H, Poulsen LR, Andreeva A, Knudsen M, Hein KL, Wiuf C, Palmgren MG, Nissen P, Nature. 2012 Oct 21. doi: 10.1038/nature11539. PMID: 23086147

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