4JRE:
reference: Crystal structure of a nitrate/nitrite exchanger., Zheng H, Wisedchaisri G, Gonen T, Nature. 2013 May 30;497(7451):647-51. doi: 10.1038/nature12139. Epub 2013 May 12. PMID: 23665960

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