6JXH:
reference: A single K(+)-binding site in the crystal structure of the gastric proton pump., Yamamoto K, Dubey V, Irie K, Nakanishi H, Khandelia H, Fujiyoshi Y, Abe K, Elife. 2019 Aug 22;8. pii: 47701. doi: 10.7554/eLife.47701. PMID: 31436534

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