1AQT:
reference: Crystal structure of the epsilon subunit of the proton-translocating ATP synthase from Escherichia coli., Uhlin U, Cox GB, Guss JM, Structure 1997 Sep 15;5(9):1219-30. PMID: 9331422

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