4AHY:
reference: Complex Gadolinium-Oxo Clusters Formed along Concave Protein Surfaces., Veelders M, Essen LO, Chembiochem. 2012 Aug 31. doi: 10.1002/cbic.201200441. PMID: 22936626

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