4PRQ:
reference: Protein assembly mediated by sulfonatocalix[4]arene., McGovern RE, McCarthy AA, Crowley PB, Chem Commun (Camb). 2014 Aug 12;50(72):10412-5. doi: 10.1039/c4cc04897k. PMID: 25068633

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