4XTO:
reference: Crystal structure of a light-driven sodium pump., Gushchin I, Shevchenko V, Polovinkin V, Kovalev K, Alekseev A, Round E, Borshchevskiy V, Balandin T, Popov A, Gensch T, Fahlke C, Bamann C, Willbold D, Buldt G, Bamberg E, Gordeliy V, Nat Struct Mol Biol. 2015 Apr 6. doi: 10.1038/nsmb.3002. PMID: 25849142

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