5UXT:
reference: Enhancing a long-range salt bridge with intermediate aromatic and nonpolar amino acids., Smith MS, Billings WM, Whitby FG, Miller MB, Price JL, Org Biomol Chem. 2017 Jul 19;15(28):5882-5886. doi: 10.1039/c7ob01198a. PMID: 28678274

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