5KPF:
reference: Protein Recognition by Functionalized Sulfonatocalix[4]arenes., Doolan AM, Rennie ML, Crowley PB, Chemistry. 2018 Jan 19;24(4):984-991. doi: 10.1002/chem.201704931. Epub 2017 Dec , 13. PMID: 29125201

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