3MPN:
reference: Structural Origins of Nitroxide Side Chain Dynamics on Membrane Protein alpha-Helical Sites ., Kroncke BM, Horanyi PS, Columbus L, Biochemistry. 2010 Nov 30;49(47):10045-60. Epub 2010 Nov 8. PMID: 20964375

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