4CBK:
reference: The c-ring ion-binding site of the ATP synthase from Bacillus pseudofirmus OF4 is adapted to alkaliphilic lifestyle., Preiss L, Langer JD, Hicks DB, Liu J, Yildiz O, Krulwich TA, Meier T, Mol Microbiol. 2014 Apr 8. doi: 10.1111/mmi.12605. PMID: 24707994

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